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Overview of particulate air pollution and human health in China:
Evidence, challenges, and opportunities
Qingli Zhang,
1
Xia Meng,
1
Su Shi,
1
Lena Kan,
2
Renjie Chen,
1,
*and Haidong Kan
1,3,
*
*Correspondence: chenrenjie@fudan.edu.cn (R.C.); kanh@fudan.edu.cn (H.K.)
Received: May 9, 2022; Accepted: August 31, 2022; Published Online: September 6, 2022; https://doi.org/10.1016/j.xinn.2022.100312
ª2022 The Author(s). This is an open access article under the CC BY license (http://creativecommons.org/licenses/by/4.0/).
GRAPHICAL ABSTRACT
PUBLIC SUMMARY
-Acute effects of PM are smaller in China compared with developed countries
-Health effects caused by PM depend on particle composition, source, and size
-There are no thresholds for the health effects of PM
-Mechanistic studies support the biological plausibility of PM’s health effects
ll www.cell.com/the-innovation
www.the-innovation.org
Review
Overview of particulate air pollution and human health in China:
Evidence, challenges, and opportunities
Qingli Zhang,
1
Xia Meng,
1
Su Shi,
1
Lena Kan,
2
Renjie Chen,
1,
*and Haidong Kan
1,3,
*
1
School of Public Health, Key Lab of Public Health Safety of the Ministry of Educa tion and NHC Key Lab of Health Technology Assessment, Shanghai Institute of Infectious Disease and
Biosecurity, Fudan University, Shanghai 200032, China
2
Bloomberg School of Public Health, Johns Hopkins University, Baltimore, Maryland, MD 21205, USA
3
Children’s Hospital of Fudan University, National Center for Children’s Health, Shanghai 201102, China
*Correspondence: chenrenjie@fudan.edu.cn (R.C.); kanh@fudan.edu.cn (H.K.)
Received: May 9, 2022; Accepted: August 31, 2022; Published Online: September 6, 2022; https://doi.org/10.1016/j.xinn.2022.100312
ª2022 The Author(s). This is an open access article under the CC BY license (http://creativecommons.org/licenses/by/4.0/).
Citation: Zhang Q., Meng X., Shi S., et al., (2022). Overview of particulate air pollution and human health in China: Evidence, challenges, and opportunities. The Innovation 3(6), 100312.
Ambient particulate matter (PM) pollution in China continues to be a major
public health challenge. With the release of the new WHO air quality guide-
lines in 2021, there is an urgent need for China to contemplate a revision of
air quality standards (AQS). In the recent decade, there has been an increase
in epidemiological studies on PM in China. A comprehensive evaluation of
such epidemiological evidence among the Chinese population is central for
revision of the AQS in China and in other developing countries with similar
air pollution problems. We thus conducted a systematic review on the epide-
miological literature of PM published in the recent decade. In summary, we
identified the following: (1) short-term and long-term PM exposure increase
mortality and morbidity risk without a discernible threshold, suggesting the
necessity for continuous improvement in air quality; (2) the magnitude of
long-term associations with mortality observed in China are comparable
with those in developed countries, whereas the magnitude of short-term as-
sociations are appreciably smaller; (3) governmental clean air policies and
personalized mitigation measures are potentially effective in protecting pub-
lic and individual health, but need to be validated using mortality or morbidity
outcomes; (4) particles of smaller size range and those originating from
fossil fuel combustion appear to show larger relative health risks; and (5) mo-
lecular epidemiological studies provide evidence for the biological plausibility
and mechanisms underlying the hazardous effects of PM. This updated
review may serve as an epidemiological basis for China’s AQS revision and
proposes several perspectives in designing future health studies.
INTRODUCTION
Rapid economic development over the past few decades in China resulted in
drastic increases in the emission of air pollutants. Although there has been contin-
uous air quality improvement following a series of stringent control policies, air
pollution is still an important public health threat in China. The Global Burden of
Disease Study estimated that in 2019, air pollution was responsible for 1.85
million deaths in China, among which 1.42 million were attributable to particulate
matter (PM).
1
In 2021, World Health Organization (WHO) tightened the global Air Quality
Guidelines (AQG), for both fine particulate matter (particulate matter with an aero-
dynamic diameter %2.5 mm, PM
2.5
) and inhalable particles (particulate matter
with an aerodynamic diameter %10 mm, PM
10
) due to ample evidence of adverse
health effects even at very low concentrations of PM. It was estimated that
1,215,000 premature deaths would have been avoided in China by achieving
the new WHO AQG target in comparison with the PM
2.5
level in 2020.
2
The current
Chinese Air Quality Standards were made with references to the interimtargets of
WHO AQG 2005. The release of the new WHO AQG may stimulate the Chinese
government to consider a new round of standard revision. A comprehensive eval-
uation of epidemiological evidence on health effects of air pollution among the
Chinese population is central to revise air quality standards (AQS) in China and
other developing countries experiencing apparent air quality problems.
During the last decade, air quality problems have led to widespread concerns in
China. To support investigations on the health effects of air pollution and their
toxicological mechanisms, the Chinese government has funded a number of pro-
jects, mainly including the National Key Research and Development Program
titled “The Cause and Control Technology of Air Pollution”and the Major Research
Program of the National Natural Science Foundation titled “Toxicology and Health
Effects of Fine Particulate Matter.”With substantial financial support, scient ificev-
idence on the health effects of air pollution, especially PM, has been rising rapidly
in China in recent years. Compared with earlier studies that were largely ecolog-
ical in nature,
3
studies published in the recent decade were of higher quality in
breadth, depth, and causality inference. A timely and systemic summary of these
scientific evidences is key to revise China’s AQS and is informative in designing
future health studies and air quality improvement projects worldwide.
We aimed to provide a comprehensive review on the up-to-date epidemiolog-
ical evidence of PM and human health in China published during the last decade.
This systemic review will include the following sections: (1) characteristics of PM
air pollution in China; (2) epidemiological evidence on short-term and long-term
associations between PM and human health; (3) findings from experimental or
quasi-experimental studies; (4) differential health effects of PM constituents,
sources, and size fractions; (5) biological mechanisms found in epidemiological
studies of PM; (6) considerations in revising China’sAQS;and(7)conclusions,
significance, and perspectives from the study.
LEVELS AND TRENDS OF PARTICULATE AIR POLLUTION IN CHINA
Rapid economic development and rigorous environmental protection actions
have driven dramatic shifts in China’s air pollution pattern over the past decades.
Due to the dominant use of coal to generate energy, air pollution in China was
once primarily characterized by coal smoke. Traffic-related air pollution (TRAP)
is now prominent due to the fast urbanization of China and the growing number
of motor vehicles. Consequently, air pollution in China has gradually changed into
a complex pattern with coal smoke, TRAP, and secondary aerosols of similar
importance.
In the past decade, the Chinese government has implemented a series of
rigorous policies and measures for air pollution control, such as the Air Pollution
Prevention and Control Action Plan (2013–2017, referred to as CAP for short) and
the Three-Year Action Plan to Win the Battle for a Blue Sky (2018–2020). Substan-
tial improvements in air quality have been achieved following these actions
(Figure 1). As shown in Figure 2, the annual average population-weighted PM
2.5
concentrations have started to decline remarkably since 2013, but were still
well beyond the global means. The annual average concentrations of PM
2.5
and PM
10
were 30 mg/m
3
and 54 mg/m
3
in 339 major Chinese cities in 2021,
which are slightly lower than the current China AQS (35 mg/m
3
for PM
2.5
and
70 mg/m
3
for PM
10
) but remain significantly higher than levels in the updated
WHO AQG (5 mg/m
3
for PM
2.5
and 15 mg/m
3
for PM
10
). The number of premature
deaths and disability adjusted life years attributable to PM
2.5
in China continues to
increase, although this increasing trend is relatively modest compared with the
global average (Figure 2).
4
EPIDEMIOLOGICAL EVIDENCE ON HEALTH IMPACTS OF PARTICULATES
IN CHINA
Short-term associations
Short-term health effects typically refer to changes of clinical or subclinical out-
comes triggered or induced by exposures that last within a few weeks. There has
been a number of time-series, case-crossover, and panel studies examining the
associations of short-term exposure to PM with a wide range of mortality,
morbidity, and subclinical outcomes in China. China included PM
2.5
in AQS for
the first time in 2012 and established the National Urban Air Quality Real-time
Publishing Plat-form (http://106.37.208.233:20035/) in 2013, which provided a
unique opportunity to conduct large, multi-city studies. These multi-city studies
provided more reliable evidence for the health effects of PM and more represen-
tative exposure-response (E-R) curves in Chinese populations.
ll The Innovation 3(6): 100312, November 08, 2022 1
Review
Mortality.Mortality is the most severe and definitive health endpoint. The as-
sociations of short-term PM exposure with daily mortality have been extensively
investigated in China. The associations between daily mean PM levels and daily
aggregate deaths were usually examined using a time-series or case-crossover
approach. Data on daily PM concentrations were generally collected from
fixed-site monitoring stations, and daily mortality data were obtained from the
Center for Disease Control and Prevention.
Emerging multi-city studies have demonstrated that short-term exposure to
PM is significantly associated with increased mortality from all-natural causes
and main cardiopulmonary diseases. Using time-series data in 38 of China’s
largest cities (sampled population >200 million), Yin et al. found a 10-mg/m
3
increase in concurrent day PM
10
concentrations to be associated with a 0.44%
increase in daily mortality, and the impact was greater on cardiorespiratory mor-
tality (0.62%) than non-cardiorespiratory mortality (0.26%).
5
Using data from 250
counties, Sun et al. conducted a time-series study and reported that heavy PM
2.5
pollution events had independent effects on daily mortality from all-cause, nonac-
cidental, circulatory, and respiratory diseases.
6
Using the largest nationwide data
in 272 Chinese cities,
7
Chen et al. reported that a 10-mg/m
3
increment in a 2-day
moving average (lag 01 days) of PM
2.5
was associated with increases of 0.22%
from all-cause mortality, 0.27% from cardiovascular mortality, and 0.29% from
respiratory mortality. The authors also observed an apparent plateauing trend
in the E-R curves at high concentrations of PM
2.5
. Another nationwide time-series
study in 267 Chinese cities reported higher mortality risks (0.44% for all-cause
mortality, 0.59% for respiratory mortality, and 0.50% for cardiovascular mortality)
per 10-mg/m
3
increase in time-weighted average PM
2.5
exposures.
8
This study
indicated that accounting for indoor exposure may help improve the estimation
of PM
2$5
-associated mortality. Multi-city studies in China generally reported a
0.22%–0.44% increase in all-cause mortality, 0.27%–0.62% increase in cardiovas-
cular mortality, and 0.29%–0.59% increase in respiratory mortality per 10 mg/m
3
increase in daily PM concentrations. The coefficients of E-R relationships were
Figure 1. Annual average concentration of PM
2.5
in China from 2013 to 2020
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2The Innovation 3(6): 100312, November 08, 2022 www.cell.com/the-innovation
www.the-innovation.org
appreciably smaller than those reported in Europe and North America. For
example, a meta-analysis including 68 time-series studies reported that the
pooled estimates per 10-mg/m
3
increase in PM
2.5
were 1.23%, 3.81%, and
2.26% in Europe, and 0.94%, 1.39%, and 0.84% in North America for all-cause, res-
piratory, and cardiovascular mortality, respectively.
9
Compared with studies focusing on mortality of the general population, few
studies in China have examined the association between PM and child deaths.
A recent national case-crossover study including 61,464 under-5 mortality cases
found that short-term exposure to PM
2.5
was significantly associated with
under-5 mortality from all natural causes as well as from specific diseases
such as preterm birth, diarrhea, pneumonia, and digestive diseases. The magni-
tude of association is considerably larger than that estimated in the general pop-
ulation, suggesting the notable susceptibility among children to the acute effects
of PM.
10
Morbidity.Compared with mortality, morbidity might be more sensitive to
reflect the acute health effects of air pollution. There are dozens of time-series
or case-crossover studies examining the short-term associations of daily PM
levels measured at fixed-site monitors with daily hospital admissions, outpatient
visits, or emergency room visits.
Most past studies focused on the short-term associations with respiratory and
cardiovascular morbidity. Using time-series data from 21 cities in southwestern
China, Qiu et al. found a 1.52% increase in hospitalizations for respiratory dis-
eases per 10-mg/m
3
increase in coarse particles.
11
Gu et al. conducted a time-se-
ries study to assess the association between air pollution and daily hospital ad-
missions in 252 Chinese cities using a national registration database of
electronic inpatient discharge records from the Hospital Quality Monitoring Sys-
tem (HQMS). The authors reported that a 10-mg/m
3
increase in same-day PM
2.5
was associated with a 0.29% increase in daily hospital admissions of respiratory
diseases.
12
In another time-series analysis using the HQMS data covering 248
Chinese cities, the authors found that a 10-mg/m
3
increase in PM
2.5
was associ-
ated with increases of 0.19%, 0.26%, and 0.26% for the same-day hospital admis-
sions of total cerebrovascular disease, ischemic stroke, and transient ischemic
attack, respectively.
13
Similarly, Tian et al. conducted a time-series study based
on the Urban Employee Basic Medical Insurance (UEBMI) in 184 major Chinese
cities and found short-term exposure to PM
2.5
to be associated with increased
hospital admissions of various cardiovascular diseases (CVDs). A 10-mg/m
3
in-
crease in PM
2.5
was associated with increased hospital admission due to overall
CVD (0.26%), ischemic heart disease (0.31%), heart failure (0.27%), heart rhythm
disturbances (0.29%), and ischemic stroke (0.29%) on the concurrent day. The
magnitudes of association for the two nationwide time-series studies were gener-
Figure 2. Average annual population-weighted
PM
2.5
, number of deaths and DALYs attributable to
PM
2.5
in China compared with global data during
2010–2019 (data source: Global Burden of Disease
Study 2019) (DALY, disability adjusted life year)
ally comparable and both observed a plateauing
pattern at higher PM
2.5
levels in the E-R relation-
ship curves.
13,14
Overall, multi-city studies in
China observed 0.29%–1.52% increases in respi-
ratory hospital admissions and 0.19%–0.26% in-
creases in cardiovascular hospital admissions
per 10-mg/m
3
increase in PM. However, a meta-
analysis including 54 time-series studies of
PM
2.5
and hospital admissions found higher esti-
mates in Europe (0.91% in cardiovascular hospi-
tal admissions and 1.90% in respiratory hospital
admissions).
9
PM has recently been associated with mental
disorders, which is becoming one of the major
contributors to disease burden. A nationwide
time-series study in 252 Chinese cities based
on data from HQMS reported that each 10-mg/
m
3
increase in PM
2.5
was associated with
0.21% increase in hospital admissions for mental
and behavioral disorders on the concurrent day. Using data from the UEBMI and
the Urban Resident-based Basic Medical Insurance (URBMI) database, Gu et al.
conducted a time-series analysis in 75 cities. They found a 0.52% increase in
depression hospital admissions per 10-mg/m
3
increase in PM
2.5
.
15
In a case-
crossover study in 26 Chinese cities, Wang et al. also reported a positive associ-
ation between short-term PM exposure and the number of hospital admissions
for depression (2.92% and 3.55% increases per interquartile range (IQR) change
of PM
2.5
and PM
10
, respectively).
16
In a time-series study using the data of 56 cit-
ies from UEBMI and URBMI database, Ma et al. found that daily hospital admis-
sions for anxiety were only marginally significantly associated with PM
2.5
.
17
In addition, other health morbidities have also been associated with short-term
PM exposure. These include diseases from endocrinal, nutritional, metabolic, ner-
vous, digestive, musculoskeletal, or genitourinary systems.
12,18,19
Subclinical outcomes.Subclinical changes can occur earlier than the presen-
tation of mortality or a morbidity event, so they are more sensitive to short-term
PM exposure. This type of evidence is very helpful to the early prevention of PM-
related diseases as well as the establishment of biological plausibility underlying
the observed associations of PM with mortality and morbidity. A number of
observational studies, mainly panel studies, have demonstrated significant asso-
ciations of short-term PM exposure with changes in a wide range of subclinical
outcomes, including fractional exhaled nitric oxide, lung function, blood pressure,
heart rate variability (HRV), renal function, and various biomarkers in bio-
specimens of healthy adults,
20–23
older individuals,
24
children,
25
and cardiopul-
monary disease patients.
26–32
Moreover, several short-term intervention studies
suggested that reducing air pollution exposure by personal protective measures
(air purifiers and particulate-filtering respirators) or air quality improvement
actions can help alleviate various subclinical effects induced by PM expo-
sure.
33–37
Apparent heterogeneity was observed for these findings, probably
due to the vast differences in study designs, characteristics of air pollution
mixture, population susceptibility, sample size, exposure assessment, outcome
measurements (e.g., laboratory tests), statistical models, and covariates
adjustment.
In summary, ample epidemiological studies have provided largely consistent
evidence for the associations between short-term PM exposure and increased
risk of mortality and morbidity for a wide range of diseases, especially those of
the cardiopulmonary system (Figure 3). The E-R relationship curves tend to be
steeper at lower concentrations and plateaued at higher levels of PM without a
discernible threshold. The magnitude of association seems to be larger among
vulnerable populations, but somewhat smaller in China than in developed coun-
tries. Despite the ubiquitous heterogeneity in studies of subclinical effects, they
Review
ll The Innovation 3(6): 100312, November 08, 2022 3
still provided evidence on the coherence and biological plausibility for the hazard-
ous effects of short-term PM exposures. The disparities in risk estimates be-
tween China and other countries might be attributable to differences in several
areas. First, PM concentrations in China were several-fold higher than those in
developed countries, and the E-R curves tended to be leveled off at higher PM
concentrations. Second, the composition and sources that determine the PM
toxicity also varied between China and other countries. For example, particles
in China have higher contents in crustal materials, dust, and constituents from
coal combustion, which may result in relatively lower toxicity than those in devel-
oped countries that mainly originated from traffic.
38,39
Third,theagestructureis
relatively younger in China in comparison to developed countries, which might
further decrease the population susceptibility to PM exposure.
Long-term associations
Long-term associations refer to chronic health effects of exposures that last
between several months and a few decades. The PM concentrations were often
estimated by an exposure model. The long-term effects of PM were usually as-
sessed using cross-sectional studies or cohort studies. Although cross-sectional
studies have reported associations of annual PM exposures with multiple
adverse health outcomes, these findings might be limited by causal inference.
In contrast, cohort studies could provide reliable epidemiological evidence on
the health effects of long-term exposure, constituting the basis for revising
AQS and conducting health risk assessment. Dozens of cohort studies conducted
in North America and Europe have demonstrated adverse health effects of long-
term PM exposure at relatively low concentrations. However, it remains uncertain
whether these associations found in developed countries are applicable to China,
a country where PM concentrations are several-fold higher than those observed
in North America and Europe.
Mortality.In the recent decade, several prospective cohort studies have
emergedinChinaandhavereportedsignificant associations of long-term
PM
2.5
exposure with mortality from all causes or a range of cardiopulmonary dis-
eases. In 2017, Yin et al. assessed the effect of long-term PM
2.5
exposure on mor-
tality risk using a nationwide prospective cohort among 189,793 Chinese men
aged 40 years or more.
40
In the Chinese Male Cohort, the hazard ratio (HR) of
mortality per 10-mg/m
3
increase in PM
2.5
was 1.09 for nonaccidental causes,
1.09 for CVD, 1.12 for chronic obstructive pulmonary disease (COPD), and 1.12
for lung cancer. This study observed nonlinear relationships between PM
2.5
and mortality outcomes with greater risks at higher concentrations. Similar esti-
mates were obtained from another prospective cohort based on the Prediction
for Atherosclerotic cardiovascular disease Risk in China (China-PAR) project.
Among nearly 117 thousand participants aged R18 years old, the China-PAR
project observed that each 10-mg/m
3
increase in PM
2.5
would increase risks of
nonaccidental mortality (HR: 1.11), cardio-metabolic mortality (HR: 1.22),
41
and
CVD mortality (HR: 1.16).
42
This cohort revealed a weak exponential E-R curve,
which showed a steeper slope at higher PM
2.5
concentrations. Based on the Chi-
nese Longitudinal Healthy Longevity Survey (CLHLS) among 13,344 adults aged
65 years and older, another nationwide prospective cohort study estimated that a
10-mg/m
3
increase in average 3-year PM
2.5
exposure led to an increase in all-
cause mortality (HR: 1.08) with a steeper E-R curve at lower concentrations.
43
In addition to the aforementioned nationwide prospective studies, some cohort
studies conducted in specific regions of China found significant associations
with mortality from all-cause, stroke, cancer, renal failure, etc.
44–46
In general,
all of these cohort studies obtained relatively comparable estimates on the mor-
tality effects of long-term PM
2.5
exposure in China (approximate 10% increase in
all-cause mortality per 10-mg/m
3
increase in PM
2.5
), and also estimates compa-
rable to those reported in developed countries.
47,48
Prevalence and morbidity.Although many cross-sectional studies have
found long-term associations between PM and prevalence of specific diseases
in China, a limited number of Chinese cohort studies have explored the effects
of long-term PM exposure on morbidity.
Chronic exposure to PM
2.5
has been shown to be associated with increased
risks of respiratory and cardiovascular diseases. Some cross-sectional studies
indicated positive associations between PM
2.5
and prevalence of chronic respira-
tory diseases, especially COPD.
49,50
To our knowledge, no cohort study in main-
land China has assessed the long-te rm effect of PM
2.5
on incidence of respiratory
diseases. Cohort studies based on the China-PAR project reported increased
morbidity risks of CVD (HR: 1.25),
42
coronary heart disease (HR: 1.43),
51
and
stroke (HR: 1.13) per 10-mg/m
3
increase in PM
2.5
.
52
Another cohort study using
data from China Family Panel Studies (CFPS) also indicated higher CVD risk asso-
ciated with long-term PM
2.5
exposure, with an HR of 1.29 per IQR (27.9 mg/m
3
)
increase of PM
2.5
.
53
The increased risk of cancer incidence, especially lung cancer, has also been
found to be associated with PM. Using data on incident lung cancer (N =
368,762) in 75 communities from the National Cancer Registration of China,
Guo et al. conducted a prospective analysis and found that the relative risk of
lung cancer incidence was 1.06 for men, and 1.15 for women per 10-mg/m
3
in-
crease in 2-year average PM
2.5
concentration.
54
Through a random 5% sample
among UEBMI beneficiaries in China from 2013 to 2016, a total of 16,483 new
lung cancer caseswere identified from 12,966,137 insurance beneficiaries. Using
this data, Zhang et al. observed that a 10-mg/m
3
increase in a 3-year PM
2.5
expo-
sure was associated with a 12% increase in lung cancer risk.
55
Using the China-
PARproject,Lietal.foundsignificantly higher lung cancer risk in participants
exposed to the second to fifth quintiles of PM
2.5
concentrations than those
exposed to the first quintile.
44
PM
2.5
has been found to increase the morbidity risk of metabolic syndromes,
such as diabetes, obesity, hypertension, and dyslipidemias. Cohort studies based
on the China-PAR project suggested that a 10-mg/m
3
increase in long-term PM
2.5
exposure was associated with increment s of 15.66% in diabetes,
56
13.5% in over-
weight/obesity,
57
and 11.0% in hypertension.
58
Some cross-sectional studies in
China also supported a positive association between prevalence of metabolic
syndrome and prolonged PM
2.5
exposure.
59,60
Mounting evidence from case-control studies, cross-sectional studies, and
cohort studies (e.g., birth cohorts) has shown that long-term exposure to PM
2.5
may impair maternal, reproductive and children’s health, and increase the risk
of multiple adverse birth outcomes. Several studies in China have linked PM
2.5
to reduced fecundity and decreased male semen quality.
61–63
Some gestational
diseases, such as hypertension
64
and diabetes mellitus,
65
were also observed to
be associated with PM
2.5
. Moreover, prenatal PM
2.5
exposure was reported to be
responsible for various adverse birth outcomes, including preterm birth,
66,67
low
birth weight,
68
fetal growth restriction,
69
premature rupture of membranes,
70
congenital heart defects,
71
and even stillbirth.
72
Additionally, PM
2.5
exposure dur-
ing pregnancy or early life was reported to impact the health status of the child
during childhood, including increased risk of respiratory diseases,
73
overweight
or obesity,
74
autism,
75
and neurodevelopmental damage.
76
Subclinical outcomes.Some cross-sectional and longitudinal studies have
linked long-term exposure to PM to selected subclinical outcomes, including
reduced lung function,
77,78
and increased blood pressure,
79,80
increased arterial
stiffness,
81
reduced renal function,
82
poor cognitive function,
83
increased level
of blood glucose
84
and lipids,
85
worsening insulin resistance,
86
elevated platelet
counts,
87
and so on. In particular, one recent study associated PM
2.5
exposure
with brain network dysfunction at multiple levels, presenting poorer reasoning
and problem-solving skills as well as higher-trait anxiety/depression.
88
In summary, there is sufficient evidence supporting the association between
long-term PM exposure and increased mortality and morbidity for a wide range
of diseases (Figure 3). Findings from nationwide prospective cohort studies
demonstrated an approximate 10% increase in all-cause mortality per 10-mg/
m
3
increase in long-term PM
2.5
exposure, levels which were generally compara-
ble in magnitude to those reported in cohort studies conducted in North America
and Europe.
47,48
The adverse effects of long-term PM exposure on subclinical in-
dicators provide some biological plausibility for the increase in mortality and
morbidity observed in cohort studies.
Experimental or quasi-experimental studies
Compared with observational studies, intervention studies are one of the
optimal designs for inferring a causal relationship because intervention studies
have a clear chronological order of exposure and events and can better control
for confounders. In the last decade, several quasi-experimental studies at the pop-
ulation level have evaluated the health benefits of air pollution abatement due to
clean air policies or large-scale events such as the Olympics. Moreover, some ran-
domized, crossover trials at the individual level have been conducted to assess
the potential protective effects of using indoor air purification, wearing face
masks, and taking dietary supplements against air pollution. Findings from these
intervention studies were valuable in inferring causality between air pollution and
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4The Innovation 3(6): 100312, November 08, 2022 www.cell.com/the-innovation
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various health outcomes and in evaluating the effectiveness of exposure mitiga-
tion measures.
Quasi-experimental studies.China has promulgated a series of stringent
clean air policies since 2013, including CAP (2013–2017), leading to dramatic im-
provements inannual air quality. During certain key prominent events, such as the
Beijing Olympics and the Nanjing Youth Olympics, aggressive air pollution control
actions were implemented in order to temporarily improve air quality. In 2003, the
Health Effects Institute provided a conceptual framework of the “chain of
accountability”describing how a regulatory action can impact emissions,
pollutant concentrations, subject exposures, and human health.
89
These policies
and events in China offered unique opportunities to conduct “accountability”
studies by evaluating whether the populations impacted by these policies
received health benefits.
With the implementation of CAP, the annual average concentrations of PM
2.5
in
China decreased substantially from 67.4 mg/m
3
in 2013 to 45.5 in 2017 mg/m
3
.By
virtue of the overlapped periods between CAP and the China Health and Retire-
ment Longitudinal Study (CHARLS), Xue et al. conducted a quasi-experimental
study in a retrospective sample of 20,000 middle-aged and older adults in
150 county-level regions. During 2013 to 2017, the CHARLS project conducted
three waves of surveys in 2011 (before CAP), 2013, and 2015 (after CAP). Using a
difference-in-differences approach, the authors found significant associations of
PM
2.5
reduction with decreased risk of depression,
90
improved blood lipid levels,
and decreased risk of dyslipidemia,
91
as well as reduced medical expenditure.
92
Another quasi-experimental study was conducted based on the CLHLS among
2,812 participants aged 60 years and older from the 2014 and 2018 waves. In
this study, 18 out of the 23 provinces set a target of reducing PM by at least
5% annually from 2014, while the r emainingfive provincesdid not set a PM reduc-
tion target. Yao et al. found a significant smaller decline in cognitive function
among individuals living in areas with a PM reduction target than those in areas
without a target.
93
During the 2008 Beijing Olympic Games, the Chinese government imple-
mented strict measures to cut air pollution emissions, resulting in a reduction
of 31% in PM
2.5
and 35% in PM
10
during the Olympic period compared with
the non-Olympic period.
94
Taking advantage of the quasi-experimental condi-
tions, some epidemiological studies evaluated the potential health benefits of
reducing air pollution. Su et al. found that air quality improvement during the
2008 Olympic Games led to reduction of CVD mortality risk in Beijing.
95
Using
data from a birth registry (83,672 term births to mothers), Rich et al. found
short-term reductions of air pollution in the eighth month of gestation during
the 2008 Olympic period to be associated with higher birth weight compared
with pregnancies during the same dates in 2007 and 2009.
96
In 125 healthy
young adults, Rich et al. observed significant improvements in soluble
P-selectin and C-reactive protein levels from the pre-Olympic period to the dur-
ing-Olympic period, and increases in systolic blood pressure and P-selectin
from the during-Olympic period to the post-Olympic period.
97
Inthesamestudy
population, Huang et al. observed large decreases in biomarkers of respiratory
inflammation and respiratory and systemic oxidative stress from the pre-Olympic
period to the during-Olympic period, while larger increases in the same bio-
markers from the during-Olympic period to the post-Olympic period were
observed.
98
The lower air pollution level during the Olympics was also reported
to be associated with decreased levels of systemic oxidative stress and respira-
tory inflammation in children.
99,100
The 2014 Nanjing Youth Olympics was another opportunity to evaluate the
health benefits of transient air quality improvement. Li et al. conducted a quasi-
experimental study among 31 healthy adults and observed that some biomarkers
of systemic inflammation significantly decreased from the pre-Olympic period to
Figure 3. Main health outcomes of particulate air pollution summarized from epidemiological studies in China
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ll The Innovation 3(6): 100312, November 08, 2022 5
the Olympic period, while they increased significantly from the Olympic period to
the post-Olympic period.
101
Health impacts of translocation have been investigated, taking advantage of
the different air pollution levels between areas. Lin et al. conducted a
biomarker-based quasi-experimental study on 26 college students traveling be-
tween Los Angeles and Beijing.
102
The investigators found that circulating levels
of six lipid peroxidation biomarkers and two inflammatory biomarkers increased
and the antioxidative activities decreased when participants traveled from Los
Angeles to Beijing. These changes in proinflammatory and pro-oxidative bio-
markers were reversed after the participants returned to Los Angeles. In the
Healthy Volunteer Natural Relocation study, 41 college students who relocated
from a suburban campus to an urban campus were enrolled and health indica-
tors were repeatedly examined beforeand after the relocation. The authorsfound
that PM
2.5
was associated with a reduction in lung function,
103
increases in blood
pressure,
104
and increases in certain inflammatory biomarkers.
105
Personalized intervention studies.In addition to the governmental efforts to
reduce air pollutant emissions, personalized mitigation measures are also helpful
to decrease exposures to particulates and mitigate their harmful effects. Several
intervention studies explored the short-term health benefits due to the use of air
purifiers, masks, and dietary supplements. These trials, using a randomized
controlled design, also shed light on the biological processes involving health ef-
fects from particulates.
The use of high-efficiency particulate air purifiers appears to be a promising
tool to decrease personal exposure to PM as people typically spend most of their
time indoors. Several randomized, double-blind, crossover studies have sug-
gested potential health benefits in reducing indoor PM concentrations through
air purification. Among 35 healthy college students from Shanghai, Chen et al.
found that a 2-day use of air purification could result in a 57% reduction of
PM
2.5
exposures (from 96.2 to 41.3 mg/m
3
). This intervention was associated
with significant decreases in blood pressure, airway inflammation, and circulating
levels of inflammatory and thrombogenic biomarkers, as well as the increases of
DNA methylation in repetitive elements and in genes of pro-inflammation, coag-
ulation, and vasoconstriction.
34,106
In another trial among 55 healthy college stu-
dents in Shanghai, the 9-day average exposure levels of PM
2.5
were 24.3 and
53.1 mg/m
3
under real and sham purification, respectively. In this trial, Li et al.
found significantly decreased levels of blood pressure, hormones, insulin resis-
tance, oxidative stress, and inflammation among individuals with lower PM expo-
sures. Metabolomics profiling further presented significant between-group differ-
ences in glucose, amino acids, fatty acids, and lipids and suggested the activation
of hypothalamus-pituitary-adrenal (HPA) and sympathetic-adrenal-medullary
axes by PM exposure.
33
Higher PM
2.5
was also associated with increases in pro-
teins or mRNA expression implicated in inflammation and vasoconstriction, and
reductions in miRNAs regulating expression of corresponding proteins or
mRNA.
107
Epigenome-wide association analysis based on the same trial has
also shown altered methylation levels of annotated genes, which were involved
in potential pathophysiological pathways of PM
2.5
exposure.
108
Several other
intervention studies assessed the health impact of using air purifiers in seniors.
For example, in a trial including 24 healthy residents of an aged-care center in
Chongqing, 48-h use of air filtration was found to be associated with significantly
decreased biomarkers of inflammation and coagulation.
109
However, in a 2-week
intervention among 35 non-smoking senior participants in Beijing, the investiga-
tors did not observe any improvements in most cardiorespiratory outcomes
including lung function, blood pressure, and HRV.
110
As a simple and practical intervention to reduce personal exposure to air pollu-
tion, especially outdoor air pollution, particle-filtration face masks or respirators
have been reported to alleviate the harmful effects of air pollution among both
healthy young adults
36
and CVD patients in China.
111
For example, in a random-
ized crossover trial among 24 healthy young adults in Shanghai, Shi et al. found
that wearing particulate-filtering respirators for 48 h was associated with
decreased blood pressure and increased HRV.
36
In another trial among 40
healthy young adults in Beijing, wearing respirators for 4 h in the underground
subway was associated with increases in most HRV parameters, and decreases
in ST segment elevation and heart rate.
35
In a larger trial involving 98 patients with
coronary heart disease, Langrish et al. found the use of a highly efficient face
mask during a 2-h walk along a city center route in Beijing to be associated
with decreased self-reported symptoms and improved cardiovascular measures
including reduced maximal ST segment depression, decreased mean arterial
pressure, and increased HRV.
111
In a trial involving 15 healthy young adults
whowalkedalongabusy-traffic road for 2 h in Beijing, results showed that wear-
ing face masks could lead to a reduction in airway inflammation.
112
Oxidative stress is widely considered to be one of the predominant pathways
underlying the adverse health effects induced by air pollution, so it is biologically
plausible that dietary supplementation with antioxidants may mitigate the harm-
ful effects of air pollution. In a randomized, double-blind, placebo-controlled trial
among 65 healthy college students in Shanghai, fish-oil supplementation pre-
sented possible cardiovascular health benefits by alleviating PM
2.5
-mediated sys-
temic inflammation, coagulation, endothelial function, oxidative stress, and
neuroendocrine stress response
113
as well as promoting skin health benefits
by mitigating PM
2.5
-mediated skin inflammation and oxidative stress.
114
Another
randomized, double-blind, placebo-controlled trial among 118 adults with
elevated blood pressure in Beijing evaluated the protective effects of L-arginine
supplementation based on a 2-h walk along a busy road. The results suggested
that the supplementation with L-arginine may reduce the adverse effects of air
pollution on blood pressure and platelet mtDNA methylation.
115,116
In summary, existing Chinese studies provide robust evidence on the favorable
short-term changes of a range of health outcomes due to personalized interven-
tion behaviors and air pollution abatement policies. However, very few experi-
mental or quasi-experimental studies evaluated long-term health benefits (espe-
cially on clinical events). Therefore, it remains to be determined whether these
favorable molecular or subclinical changes reported can be translated into clinical
benefits (e.g., reduced mortality and morbidity).
Differential health effects of particulate matter constituents, sources, and
size fractions
Most epidemiological studies on PM focused on the health effects of total
mass concentrations. However, the toxicity of PM was determined by features
related to chemical constituents, sources, and size fractions. Identifying the phys-
icochemical characteristics that have critical toxicity and health effects is impor-
tant to conduct accurate health risk assessments, develop targeted air quality
management strategies, and tailor localized public health responses.
PM
2.5
is a mixture comprising a complex chemical composition, including
organic carbon, inorganic carbon, inorganic ions, and metallic or non-metallic
elements, each of which might have independent or interactive effects with
each other. Because the components are closely related to specific sources, un-
derstanding the relative importance of various constituents is of great signifi-
cance for identifying the more harmful sources. Some epidemiological studies
in China have attempted to identify key constituents responsible for PM
2.5
-
related health effects. Using data from Shanghai Health Insurance Bureau,
Qiao et al. performed a time-series study and reported that organic carbon
and elemental carbon have robust associations with daily emergency room
visits. In a panel study of 40 college students in Beijing, Wu et al. found that
short-term exposure to carbonaceous fractions, some ions and metals were
closely related to increased blood pressure,
104
and certain metallic constituents
may induce impairment in lung function,
117
alterations in circulating biomarkers
of endothelial function,
118
and oxidative stress.
119
In a panel study among 30
COPD patients in Shanghai, Chen et al. found organic carbon, elemental carbon,
nitrate, and ammonium to be significantly associated with increased airway
inflammation and decreased DNA methylation of encoding genes.
32
Several
cohort studies have also reported the long-term effects of specific constituents.
For example, in a prospective analysis of 90,672 adults across 161 districts/
counties in China, black carbon, organic matter, nitrate, ammonium, and sulfate
had appreciably larger HRs of mortality from CVD and its subtypes than PM
2.5
total mass, while soil dust had no increased risk.
120
Another nationwide cohort
of 14,331 adults (in CFPS) has demonstrated that black carbon, nitrate, ammo-
nium, and sulfate were mainly responsible for the association between long-
term exposure to PM
2.5
and increased risks of total CVD and hypertension inci-
dence.
53
Using data from a nationwide birth cohort of 3,723,169 live singleton
births in 336 Chinese cities, He et al. found organic carbon and black carbon to
be associated with higher preterm birth risk.
121
Although the results are not al-
ways consistent, transition metals, carbonaceous fractions, nitrates, and sul-
fates are likely to be responsible for the adverse effects of PM, suggesting
that sources from fossil fuel combustion might be major contributors to
adverse health effects.
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Size fractionis another important feature to determinethe health effects ofPM.
It is assumed that PM of a smaller size has higher toxicity as these particles have
larger surface area, higher reactivity, and are more likely to penetrate deeper into
the respiratory system. Moreover, the nano-scale particles might even be able to
be absorbed into the blood after inhalation. Unlike PM
2.5
and PM
10
,particulatesof
a smaller size were not criteria pollutants, and their health effects were not
commonly investigated because of the lack of environmental monitoring data.
As a major mass contributor to PM
2.5
(over 80% of PM
2.5
in China), PM
1
(partic-
ulatematterwithaerodynamicdiameter%1mm) has recently been reported to
be related to various adverse outcomes, including cardiovascular morbidity
and mortality,
122,123
hypertension,
124
asthmatic symptoms,
125
metabolic syn-
drome,
60
autism,
75
and preterm birth.
126
The health effects of PM
1
were further
found to be independent of other air pollutants
127,128
and may be more harmful
than PM
2.5
.
122,123
PM also contains a large number of nano-scale particles, such
as those <0.1 mm(i.e.,ultrafine particles [UFPs]). Although these particles ac-
count for only a very small mass fraction of PM
2.5
, they contribute to the largest
proportion of number concentrations. Recent evidence from time-series or panel
studies conducted in megacities in China indicated that short-term exposure to
UFPs was associated with a series of cardiopulmonary diseases or their bio-
markers.
129–133
Some studies in China further indicated that the detrimental ef-
fects of UFPs were independent of othe r air pollutants
132
and stronger than larger
particles.
132,133
The WHO provided a qualitative statement of UFPs in 2021 for the
first time, but did not conclude a particular AQG for UFPs due to insufficient epide-
miological evidence.
134
In summary, although increasing epidemiological studies evaluated the asso-
ciations of constituent-specific and size-segregated particles with a variety of
health outcomes in China, no consensus was reached on the specific chemical
compositions or size ranges with predominant health hazards. A better under-
standing of the potentially differential health effects from various particle sources
is of great value to develop more targeted policies to reduce air pollutant emis-
sions. However, there is a lack of epidemiological evidence directly linking
different particle sources to adverse health outcomes.
AN OVERVIEW OF HUMAN-BASED FINDINGS ON BIOLOGICAL
MECHANISMS
Human-based mechanistic evidence is valuable forinferring causality as it pro-
vides biological plausibility. It is also helpful in identifying the early-effect bio-
markers and the key physiopathological pathways that may be used in the pre-
vention and intervention of PM-related diseases. A number of observational,
experimental, and quasi-experimental studies in China have extensively explored
the biological mechanisms underlying PM-related effects in various subpopula-
tions. Biomarkers implicated in oxidative stress,
33,98,102,135,136
inflammatory
response,
20,23,32,97,107,137–139
endothelial dysfunction,
107,140
thrombosis and
coagulation,
34,107,109,141,142
and epige netic changes
106,107,143,144
were frequently
reported to be associated with changes in PM exposures (Figure 4). These bio-
markers were mostly examined in studies of short-term exposures, which still
need to be confirmed by prospective cohort studies. Althoughmost of these bio-
markers or proposed pathways were not novel in the literature, the molecular
epidemiological findings in China replicated mechanistic evidence in a highly
polluted background.
With the development of high-throughput techniques, emerging studies in
China investigated the biological mechanisms of PM using omics, such as
genomics,
88
epigenomics,
108,145,146
transcriptomics, metabolomics,
33,147–150
lip-
idomics,
67
and microbiomics.
20,151–155
An omics analysis allows a hypothesis-
free assessment of potential biological mechanisms, which is helpful to discover
novel biological pathways and biomarkers. For example, in a randomized,
Figure 4. Biological pathways underlying the health effects of particulate air pollution proposed in molecular epidemiological studies of China Abbreviation: PM, particulate m atter;
ROS, reactive oxygen species; HPA axis: hypothalamus-pituitary-adrenal axis; SAM, sympathetic-adrenal-medullary axis.
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ll The Innovation 3(6): 100312, November 08, 2022 7
double-blind, crossover trial among 55 healthy college students by Li et al., the
metabolomic analysis identified a range of metabolic changes indicative of acti-
vations of the HPA and sympathetic-adrenal-medullary axes after short-term
exposure to PM
2.5
.Thisnovelfinding added new mechanistic evidence for under-
standing the health effects of PM
2.5
.
33
Other single-omics analyses revealed the
alterations of a broad spectrum of biomolecules and unveiled some biological
pathways triggered by air pollution.
107,148,156
However, very few investigations
explored the systemic alterations induced by air pollution using the multi-omics
approach. In a randomized crossover trial of TRAP, the transcriptomics, prote-
omics, metabolomics, and lipidomics were incorporated simultaneously, and
the changes in gene expression, proteins, metabolites, and lipids in response to
short-term exposure to TRAP were mapped. The authors found that dozens of
regulatory pathways were activated after TRAP exposure including some well-
known pathways related to air pollution, such as inflammation, oxidative stress,
coagulation, endothelin-1 signaling, renin-angiotensin signaling, and lipid meta-
bolism, as well as certain novel pathways such as growth hormone signaling,
adrenomedullin signaling, arachidonic acid metabolism, and vascular smooth
muscle cell proliferation.
157,158
It should be noted that most available mechanistic evidence in China was
derived from observational studies or intervention studies conducted in real-
word environments, which may, to some extent, be subject to residual confound-
ing. In addition, almost all mechanistic studies focused on the short-term
effects of PM, while the long-term effects were rarely investigated. More
controlled-exposure trials and prospective cohort studies are warranted to eluci-
date the biological mechanisms underlying the health effects. A multiple-omics
approach, especially from mediation or “meet-in-the middle”analysis, is encour-
aged to understand the global molecular changes and their causality relations
more comprehensively in the systemic response induced by PM. Multiple
cross-validation is also needed to improve the reliability and reproducibility of
the findings.
CONSIDERATIONS IN REVISING CHINA’S AIR QUALITY STANDARDS
AQS is the cornerstone of air quality management. In China, it is the Ministry
of Ecology and Environment’s responsibility to update the AQS regularly. The
current China’s AQS (GB 3095-2012) was issued in 2012 with certain amend-
ments made in 2018. Whether and when to start a new round of standard re-
visions has been put on the agenda of the Ministry of Ecology and Environment.
The release of the new WHO AQG has inevitably triggered more discussions. As
the WHO recommended, governments across the world, including China, can
use the AQG in different ways depending on the local technical capabilities, eco-
nomic capacity, air quality management policies, and other political and social
factors.
Scientific evidence on the health effects of air pollution is essentially the corner-
stone in setting/revising the AQS. In updating China’s AQS, the state-of-the-art sci-
ence of the association between air pollution and health should be fully consid-
ered, with special emphasis on Chinese epidemiological data, whenever
available. During the process of revising AQS, an extensive assessment of the
best available evidence on E-R relationship is indispensable. Some factors, like
population characteristics, climate, and air pollution level and sources, may
modify the E-R relationship. For example, the acute health risks observed among
the Chinese population are somewhat smaller in magnitude, per amount of pollu-
tion, than the risks found in developed countries. Therefore, local evidence is
particularly important in revising China’sAQS.
In the meantime, revising China’s AQS simply based on epidemiological
evidence might uncover that the intended standards are not achievable in
practice. Facing the reality of relatively high air pollution levels and the de-
mand for rapid economic development, it might be practical to set China’s
AQS for major air pollutants using interim targets. Given the large dispar-
ities in air pollution levels and E-R relationships across China’s various re-
gions, applying regional AQS should be encouraged. Also, the issue of envi-
ronmental justice and social equity should be considered in the
development of China’s AQS. For instance, the Chinese population is rapidly
aging, and so China’s AQS should protect not only the general population,
but also vulnerable subgroups such as those with chronic conditions (e.g.,
respiratory or cardiovascular diseases) and older people. Nevertheless,
more in-depth research and discussion will be needed in order to have a
balance between the ideal target value and practical feasibility in China.
CONCLUSIONS, SIGNIFICANCE, AND FUTURE PERSPECTIVES
During the last decade, epidemiological studies on particulate air pollution and
human health have been growing in China, comprising large, multi-city studies,
prospective cohort studies, experimental and quasi-experimental studies, and
molecular epidemiological studies. These studies have provided convincing evi-
dence that particulate air pollution is associated with a wide range of adverse
health effects, especially on the cardiopulmonary system (Table 1, graphical ab-
stract). According to this comprehensive review on epidemiological studies con-
ducted in China during the last decade, we can derive the following conclusions.
Specifically, (1) short-term and long-term PM exposure increase the mortality and
morbidity risk without a discernible threshold; (2) the magnitude of long-term as-
sociations with mortality observed in China were comparable with those in devel-
oped countries, whereas the magnitude of short-term associations were appre-
ciably smaller; (3) governmental clean air policies and personalized mitigation
measures are potentially effective in protecting public and individual health, but
need to be confirmed using mortality or morbidity outcomes; (4) particles of
smaller size range and those originating from fossil fuel combustion appear to
show larger relative health risks; and (5) molecular epidemiological studies pro-
vide evidence for the biological plausibility and mechanisms underlying hazard-
ouseffectsofPM.
These findings have implications for policy formulations and further investi-
gations. First, the adverse effects of PM
2.5
appear to have no discernable
“safe”threshold, which indicated the necessity of the continuous improvement
of China’s air quality. Second, the E-R association was found to vary by
geographical area, which indicates that local specific conditions should be
considered in future AQS revision, risk assessment, disease burden estimation,
and policy formulation. Third, individuals with chronic conditions (e.g., respira-
tory or cardiovascular diseases), children, and older people were found to be
vulnerable to the impacts of PM. This revelation has implications to protect sen-
sitive populations and explore the mechanisms underlying the susceptibility.
Finally, PM appears to adversely affect various human systems, which has
enhanced the understanding of the spectrum of diseases affected by PM.
Epidemiological and toxicological studies are warranted to further clarify their
causal relationships in the future.
Although the adverse health effects of PM have been well documented in
China, several questions or challenges remain to be solved in human-based
studies, especially for stronger causality inference. Firstly, a cohort study is one
of the optimal designs to infer a causal relationship because it could observe
the natural process from long-term air pollution exposure to the incidence of
adverse health outcomes. Evidence from cohort studies plays a crucial role in
the formulation of AQS and assessment of health risks or disease burden.
Although a large number of cohort studies conducted in developed countries
have reported various hazards of long-term PM exposures, it remains uncertain
whether these associations are also applicable in China. Although some recent
prospective cohort studies in China have examined the long-term effects of
PM exposure on total and cardiopulmonary mortality or morbidity, evidence
from cohort studies is still lacking for examining mortality and morbidity due to
a full spectrum of diseases. Secondly, accountability studies that evaluate long-
term health benefits of clean air policies and intervention studies that reduce
individual’s exposure are also needed to clarify the termination effects of air pollu-
tion. The applications of the difference-in-differences approach and the random-
ized crossover design have been shown to further improve the causality. Thirdly,
controlled-exposure human trials are particularly useful to establish the biological
causation for the adverse health effects of air pollution. Fourthly, human-based
evidence on specific particle size ranges, chemical compositions, and sources
are still preliminary, and investigations based on large-scale prospective cohorts
and use of more advanced statistical approaches are particularly helpful. Fifthly,
there is a lack of cle ar understanding, especially from an exposomics perspective,
on how external PM or its constituents enter the body, induce systemic biological
functions, and ultimately result in a disease. Finally, the finer spatiotemporal res-
olution for exposure assessment, especially the personal exposure measurement
or modeling, should be encouraged to improve the precision of estimated asso-
ciations with health outcomes.
The coronavirus disease 2019 (COVID-19) pandemic has become a major
health crisis worldwide. PM
2.5
may not only act as a vital carrier and promote
the persistence of the virus in the air, but it could also decrease immune response
and increase susceptibility of viral infection. Recent epidemiological studies have
shown that both short-term and long-term exposure to PM
2.5
are related to the
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8The Innovation 3(6): 100312, November 08, 2022 www.cell.com/the-innovation
www.the-innovation.org
increase in spread and lethality of COVID-19.
159–161
However, these epidemiolog-
ical studies were subject to apparent limitations that may potentially mask true
associations. These limitations mainly include the ecological or cross-sectional
nature in design, as well as the inability to control for some critical factors respon-
sible for the spread and lethality of COVID-19 (e.g., sociodemographic character-
istics, control policy, population density, and the healthcare system capacity). On
the other hand, while air quality during the lockdown period improved and the
subsequent health benefits have been assessed,
162
these associations were
rarely examined in an epidemiological study. Therefore, the interactions of partic-
ulate air pollution and the COVID-19 pandemic warrant further investigations to
better address the two pressing public health crises.
Climate change is widely considered the largest global public health chal-
lenge. The sources emitting greenhouse gases can also produce air pollutants,
and they can interact with air pollution in inducing health effects. Accordingly,
climate mitigation policies could also result in health co-benefits by virtue of
reducing air pollution. As the largest emitter of carbon dioxide, China
announced its ambitious climate commitment in September 2020 to achieve
carbon peak by 2030 and to achieve carbon neutrality by 2060. The ambitious
“double carbon”goal is a powerful driver for improving air quality in China. It
was estimated that if China achieves the carbon neutrality goals in 2060, the
annual average PM
2.5
level (30 mg/m
3
in 2021) will be reduced to about
8mg/m
3
, which is very close to the new WHO AQG target (5 mg/m
3
), and
approximately 78% of the Chinese population will experience an annual average
PM
2.5
level below 10 mg/m
3
.
163
Air quality improvement actions aiming to
reduce fossil fuel consumption will also promote low-carbon development.
The achievement of carbon neutrality and the reduction of air pollution will in
turn lead to considerable health co-benefits. Therefore, air quality, climate
change, and health effects should be considered simultaneously to maximize
public health benefits.
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Table 1. Overall summary of epidemiological evidence on the health effects of fine particulate air pollution in China
Short-term (hours to days) Long-term (months to years)
Number Quality Consistency Number Quality Consistency
Mortality
All-cause +++ +++ +++ ++ +++ +++
Respiratory disease +++ +++ +++ ++ ++ +++
Cardiovascular disease +++ +++ +++ ++ ++ +++
Morbidity
Respiratory disease + ++ ++ ++ + +++
Cardiovascular disease ++ ++ +++ +++ ++ +++
Mental disorders + ++ ++ ++ ++ +++
Lung cancer ––– ++ +++ +++
Metabolic syndrome ––– ++ ++ +++
Adverse reproductive outcomes ––– +++ +++ ++
Chronic kidney disease ––– ++++
Subclinical outcomes
Reduced lung function +++ ++ ++ ++ ++ +++
Increased blood pressure +++ +++ ++ ++ + +++
Reduced heart rate variability +++ +++ ++ –––
Increased arterial stiffness ––– +++
Reduced renal function ––– +++
Poor cognitive function ––– +++++
Increased blood glucose ––– +++
Increased blood lipids ––– +++++
Insulin resistance ––– +++++
Number: +++ means many relevant studies (>10), ++ means several relevant studies (3–10), + means only 1 to 2 relevant studies.
Quality: +++ high (R3 trial/quasi-experimental study/multi-cities studies for short-term effects, or R3 cohort studies for long-term effects), ++ moderate (1–2 trial/
quasi-experimental study/multi-cities studies for short-term effects, or 1 to 2 cohort studies for long-term effects), + low (all studies are observational in nature and
no multi-cities studies).
Consistency: +++ almost completely consistent, ++ partly consistent, + completely inconsistent.
–, no relevant studies.
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ll The Innovation 3(6): 100312, November 08, 2022 9
8. Dong, Z., Wang, H., Yin, P., et al. (2020). Time-weighted average of fine particulate matter
exposure and cause-specific mortality in China: a nationwide analysis. Lancet Planet.
Health 4, e343–e351.
9. Atkinson, R.W., Kang, S., Anderson, H.R., et al. (2014). Epidemiological time series studies of
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ACKNOWLEDGMENTS
This work was supported by the National Natural Science Foundation of China
(92043301, 91843302 and 92143301), and the Shanghai Committee of Science and Tech-
nology (21TQ015).
AUTHOR CONTRIBUTIONS
R.C. andH.K. conceivedand designedthe research andrevised the manuscript. Q.Z. wrote
the original draftand revised it. X.M andS.S completed exposure evaluation ofPM
2.5
levelsin
China. L.K. revised and improved the manuscript.
DECLARATION OF INTERESTS
The authors declare no competing interests.
LEAD CONTACT WEBSITE
Renjie Chen: http://sph.fudan.edu.cn/employee/60
Haidong Kan: http://sph.fudan.edu.cn/employee/14
Review
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