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Open Journal of Air Pollution, 2014, 3, 33-41
Published Online June 2014 in SciRes. http://www.scirp.org/journal/ojap
http://dx.doi.org/10.4236/ojap.2014.32004
How to cite this paper: Mukhopadhyay, K., Ramasamy, R., Mukhopadhyay, B., Ghosh, S., Sambandam, S. and Balakrishnan,
K. (2014) Use of Ventilation-Index in the Development of Exposure Model for Indoor Air Pollution—A Review. Open Journal
of Air Pollution, 3, 33-41. http://dx.doi.org/10.4236/ojap.2014.32004
Use of Ventilation-Index in the Development
of Exposure Model for Indoor Air
Pollution—A Review
Krishnendu Mukhopadhyay1, Rengaraj Ramasamy1, Banani Mukhopadhyay2,
Santu Ghosh1, Sankar Sambandam1, Kalpana Balakrishnan1
1Department of Environmental Health Engineering, ICMR Center for Advanced Research on Environmental
Health: Air Pollution, Sri Ramachandra University, Chennai, India
2Department of Chemistry, Women’s Christian College, Chennai, India
Email: krishnendu@ehe.org.in, rengaraj@ehe.org.in, banalata97@rediffmail.com, santu@ehe.org.in,
sankars@ehe.org.in, kalpanasrmc@ehe.org.in
Received 8 March 2014; revised 8 April 2014; accepted 16 April 2014
Copyright © 2014 by authors and Scientific Research Publishing Inc.
This work is licensed under the Creative Commons Attribution International License (CC BY).
http://creativecommons.org/licenses/by/4.0/
Abstract
In indoor environment, emission factor of the cooking fuel plays a vital role in determining corre-
lation between exposure assessment and health effects. Both indoor and outdoor air pollution
exposures are widely influenced by the ventilation status. An optimum control of the air change
rate has also significant impact on the exposure pattern. A number of studies revealed that the
indoor particulates and gaseous exposures, resulting from the combustion of various cooking fu-
els, are associated with significant adverse health effects on pregnant mothers and new born ba-
bies. The impacts of ventilation status on air pollution exposure in households’ kitchens or living
rooms have not been explored enough. Except a few studies with concrete rooms, especially in in-
dustries, no other studies have been established on the correlation between the ventilation index
and air pollution exposure. The intent of this review is to discuss reported findings focused on the
ventilation and exposure to air pollution. This will obviously help better understanding to mod-
ulate exposure profile in household condition using simple tool of ventilation measurement.
Keywords
Ventilation Index, Exposure, Air Change Rate, Air Pollution, Health Effects
1. Introduction
Human occupancy and activity spoil the air quality in the occupied rooms and give a sense of discomfort to the
K. Mukhopadhyay et al.
34
occupants. Unless the contaminated indoor air is replaced by the fresh air, it may adversely affect the comfort,
health and the efficiency of the occupants. Occupants may feel suffocation and complain of headache, drowsi-
ness and inability to concentrate.
Ventilation is a critical component of green homes and it plays a vital role in the assessment of human expo-
sure to air pollutants in indoor environment. It is reported that indoor air has a higher concentration of gases and
particles compared to outdoor air, typically due to inadequate ventilation combined with high temperature and
humidity levels, which can hold a greater concentration of gases. For example, the average outdoor radon level
has been found to be 0.4 pCi/L in comparison to the average indoor radon level 1.3 pCi/L [1]. Globally, 4.3 mil-
lion deaths were attributed to exposure to indoor air pollution in developing countries in 2012, almost all in low
and middle income countries [2]. Low- and middle-income countries in the WHO South-East Asia and Western
Pacific Regions had the largest air pollution-related burden in 2012, with a total of 3.3 million deaths linked to
indoor air pollution and 2.6 million deaths related to outdoor air pollution [3].
According to the United States Environmental Protection Agency (USEPA), human exposure to indoor air
pollutants may be 2 to 5 times—occasionally more than 100 times higher than outdoor pollutant levels. Indoor
air pollutants have been ranked among the top five environmental risks to public health [4]. This is because a
home’s interior accumulates and concentrates pollutants given off by finishes, furnishings and the daily activi-
ties of the occupants. Meteorological parameters such as room temperature, humidity, air density, wind direction
and physico-chemical parameters like vapor pressure, specific gravity, diffusion, dispersion, partition co-effi-
cient, evaporation, vaporization etc. contribute a lot in developing exposure model. Other important factors are
pollution source, room volume, ventilation type and exposure time [5] [6].
The “Ventilation Index” is a common term used in air pollution. It is a numerical value related to dispersing
potential for airborne pollutants in a certain local atmosphere. It is based on both the existing wind speed in the
mixed layer and the mixing height. The mixed layer is the surface layer of air that is turbulent and well mixed.
The mixing height is the thickness of this mixed layer. Stronger wind speeds and thicker mixed layers will pro-
duce higher venting indices. For convenience, the Ventilation Index is converted to a scale of 0 to 100 [7].
But, in normal indoor environment, the air pollution exposure concentration depends largely on the emission
factor of the cooking fuel. An emission factor is a representative value that attempts to relate the quantity of a
pollutant released to the atmosphere with an activity associated with the release of that pollutant. An air quality
emission factor is then related between the amount of pollution produced and the amount of raw material
processed. These factors are usually expressed as the weight of pollutant divided by a unit weight, volume, dis-
tance, or duration of the activity emitting the pollutant. Such factors facilitate estimation of emissions from var-
ious sources of air pollution and to document the emission gradient in indoor environment, measuring ventila-
tion status would be a better option.
Information on emission sources may be available from household questionnaire administration and by the
observation of the person engaged in indoor air monitoring process. In general, these processes can be grouped
into five categories namely combustion, manufacturing, solvent evaporation, storage and fugitive.
If the concentration of a contaminant in a fuel is known, emissions of that contaminant can be calculated by
assuming all of the contaminant emitted prior to the application of an emission control. It should be noted that
some of the contaminants require further analysis to determine the portion emitted to the atmosphere, since some
of these contaminants may end up in various physical or chemical states and not emitted to the atmosphere. The
general equation for the mass balance approach is:
–Me Mi Mp Ma Mc=−−
(i)
where, Me = Mass of the compound emitted; Mi = Mass of the compound in the raw material feed; Mp = Mass
of the compound in the finishing product; Ma = Mass of the compound accumulated in the physical or chemical
state; Mc = Mass of the compound captured for recovery or disposal.
Basically, an emission factor is the contaminant emission rate relative to the level of source activity. Facility
specific established emission factors (mass of emission per unit time, mass of emission per input material flow,
or mass of emission per unit output production) will be applicable to the measured processes or similar equip-
ment/processes of other facilities when the operating conditions are comparable. Generic emission factors are
commonly used when site-specific source monitoring data are unavailable.
The basic equation used in an emission factor calculation is:
[ ]
100 100
xx x
E BQ EF CE=×× −
(ii)
K. Mukhopadhyay et al.
35
where: Ex = Emission of contaminant x, kg; BQ = Activity rate or base quantity (BQ), BQ unit; EFx = Uncon-
trolled emission factors of contaminant x, kg/BQ unit; CEx = Overall emission control efficiency of contaminant
x, % or
xx
E BQ CEF= ×
(iii)
where: Ex = Emission of contaminant x, kg; BQ = Activity rate or base quantity (BQ), BQ unit; CEFx = Con-
trolled emission factors of contaminant x, kg/BQ unit. ER is further defined as the product of the control device
destruction or removal efficiency and the capture efficiency of the control system. When estimating emissions for
a long time period, both the device and the capture efficiency terms should account for upset periods as well as
routine operations [8].
Data from source-specific emission tests or continuous emission monitors are usually preferred for estimating a
source’s emissions because those data provide the best representation of the tested source’s emissions. However,
test data from individual sources are not always available and, even then they may not reflect the variability of
actual emissions over time. Thus, in spite of their limitations, emission factors are frequently considered as the
best or only method available for estimating emissions.
For estimating ventilation index, the parameter air change per hour (ACH) has also been used in several facil-
ities to describe the volume of air in a building that is replaced per hour through ventilation. As per the Association
of German Engineers (VDI), air change is defined as the ratio of air supply Q(t) into a zone (i.e. a room or space)
in relation to the volume of this zone VR (room volume)and is generally expressed as air change per hour [h–1] or
[ACH]. The following equation expresses this definition:
() ( )
t Q t VR
λ
=
(iv)
where, λ(t) is the ventilation rate or air change rate [h−1], Q(t) is the air supply into a room [m3/h], VR is the room's
volume [m3], and t = time [h] [9]. Using this equation they developed a model for air change in indoor room
quantified by tracer gas concentration. The basis for the description of the relationship is the mass balance equa-
tion. This equation expresses that the mass and—in a fixed volume—the concentration of a tracer gas can only
change when either more tracer gas is added to the original amount or tracer gas is removed by elimination
processes. Three common methods exist for the determination of air exchange rate (ACR) using tracer gases
namely, the concentration decay method, the constant injection method, and the constant concentration method.
The very limited data available suggest that inflammation, respiratory infections, asthma symptoms, and short
term sick-leave increase with lower ventilation rates. It is also found that ventilation rates above 0.5 air change rate
per hour in homes are associated with a reduced risk of allergic manifestations among children in a Nordic climate
[10]. It means ACH above 0.5 attains disperse potential of the toxicants present in indoor environment that is
effective in reducing the risk of exposure and health outcomes.
On the other hand, the ventilation effectiveness describes the relation between the pollution concentrations in
the supply air, the extract air and the indoor air in the breathing zone (within the occupied zone). It is defined as
CETA CSUP
VCIDA CSUP
ε
−
=−
(v)
where εv is the ventilation effectiveness, CETA is the pollution concentration in the extract air, CIDA is the pollu-
tion concentration in the indoor air (breathing zone within in the occupied zone) and CSUP is the pollution con-
centration in the supply air. The ventilation effectiveness depends on the air distribution and the kind and loca-
tion of the air pollution sources in the space. It may therefore have different values for different pollutants. If
there is complete mixing of air and pollutants, the ventilation effectiveness is one [11].
Carbon dioxide has been an effective choice as a good tracer gas since it holds almost similar molecular weight
as of air and is mixed well with it. The only problem of using CO2 is its high back ground concentration of ap-
proximately 350 ppm and it’s exhaled amount by the people. Other tracer gases like hydrogen gas, water vapour,
sulfur hexafluoride etc. have also been used in various ventilated spaces [12]. Sometimes, application of constant
tracer gas concentration has been applied to estimate ACH with specific dosing and control system. The advantage
of the constant concentration method is that, even with short-term changes of air supply, concentration can be
detected. If a tracer gas is injected into a zone of the space, its concentration in this zone can be calculated by the
following conservation equation with the assumption of uniform tracer-gas concentration in the zone:
dc
V QC m
dt +=
(vi)
K. Mukhopadhyay et al.
36
where, V is the zone volume, C is the tracer-gas concentration, Q is the ventilation rate to the zone, and m the
injection rate of the tracer gas. In the tracer-gas-concentration decay method, the tracer gas will decay due to
ventilation after injection into the space is stopped [13]. This study proposed a modified tracer-gas-concentration
decay method for measuring the ventilation rate in large, long, and narrow paces. The modified method also en-
courages the use of mixing fans in the space to achieve a more uniform distribution of tracer-gas concentration and
has been compared to constant concentration method, which is regarded as the most accurate one. The modified
method measured was reported about 5% - 10% lower ventilation rate. This study may act as an important tool in
developing ventilation index and exposure model in rural and urban household situations with different moni-
toring parameters persisting in air matrices, too.
Liuliu Du et al. conducted a study in the homes of Detroit, Michigan investigating ACRs and interzonal flows.
The studied households were primarily low income and minority, and each had a child with asthma. In the houses’
living area, ACRs average was found to be 0.73 ± 0.76 h−1 (median = 0.57 h−1, n = 263). In the child’s bedroom,
ACRs were substantially higher with the average of 1.66 ± 1.50 h−1 (median = 1.23 h−1, n = 253). ACRs were
reported to be positively associated with recent sweeping and dusting, and indoor PM concentrations, and nega-
tively associated with house size, the presence of a central air conditioner and smokers, indoor CO2 and VOC
concentrations [14]. Therefore, the ventilation index and consequent exposure model could be developed using
other relevant information like house characteristics, fuel type & consumption, temperature etc. by measuring
indoor PM concentrations and wind speed.
To calculate the ACH of a building, the use of American Society of Heating, Refrigerating and Air Condi-
tioning Engineers (ASHRAE) minimum limit of 0.35 ACH of the building’s volume is generally adopted to de-
termine the safety and acceptable indoor air quality of its design.
Inadequate ventilation can increase indoor pollutant levels by not bringing in enough outdoor air to dilute
emissions from indoor sources and by not carrying indoor air pollutants out of the home. High temperature and
humidity levels can also increase concentrations of some pollutants. In indoor environment, some sources such
as building materials, furnishings, and household products like air fresheners release pollutants more or less
continuously. Other sources, related to activities carried out in the home, release pollutants intermittently. These
include smoking, the use of unvented or malfunctioning stoves, furnaces, or space heaters, the use of solvents in
cleaning and hobby activities, the use of paint strippers in redecorating activities, and the use of cleaning prod-
ucts and pesticides in house-keeping. High pollutant concentrations can remain in the air for long periods after
some of these activities. If too little outdoor air enters a home, pollutants can accumulate to levels that can pose
health and comfort problems. Unless they are built with special mechanical means of ventilation, homes that are
designed and constructed to minimize the amount of outdoor air that can “leak” into and out of the home may
have higher pollutant levels than other homes. However, because some weather conditions can drastically re-
duce the amount of outdoor air that enters a home, pollutants can build up even in homes that are normally con-
sidered “leaky” [15].
M. Ucci et al. tried to assess the link between asthma and low ventilation rates in housing of United Kingdom.
But it was found to be clearly inconclusive. The possible assumption was that the air tightness of ener-
gy-efficient dwellings might have an adverse impact on indoor air quality, provided the main pollution emitted
from indoor source. In the study, the other aims were to establish the minimum ventilation rate required in a
dwelling in order to control levels of moisture-related pollutants like dust mites, mould etc. that could reduce the
number of respiratory hazards. Here also no significant association could be found between asthma prevalence
and fitness of ventilation [16].
Sundell et al. found that elevated concentrations of House Dust Mite (HDM) allergen in mattress and floor
dust were associated with the difference in absolute humidity between indoor and outdoor air, as well as with
low air-exchange-rates of the home, especially in the bedroom. The study concluded that in regions with a cold
winter climate, there was a correlation between infiltration and mite infestation; but air-flow rates related to
number of people in the home appeared a stronger indicator of HDM infestation than air-flow rates related to
home volumes [17]. Emenius et al. examined the impact of building characteristics and indoor air quality on re-
current wheezing in infants. They found that whilst building-related exposures appear to have a major impact on
children’s health, this was not primarily explained by differences in ventilation systems, air change rate or HDM
infestation [18]. Nielsen reported ventilation measurements made in a random selection of 11 schools in Den-
mark. Measurements were made in 2 classrooms for 3 consecutive days. The average ventilation rate was 6.4
L/s-person with a range of 1.8 - 15.4 L/s-person [19].
K. Mukhopadhyay et al.
37
Ventilation rates are rarely measured in the process of indoor air measurements in rural and urban households,
though inadequate ventilation is often suspected to be an important condition leading to reported health symp-
toms. The ASHRAE Standard recommends a minimum ventilation rate of 8 L/s-person (15 cfm/person) for
classrooms. Given typical occupant density of 33 per 90 m2 (1000 ft2) and a ceiling height of 3 m (10 ft), the
current ASHRAE standard would require an air exchange rate of about 3 air changes per hour (ACH) for a
classroom.
Among various studies performed in schools earlier, some studies provided only aggregated data while others
included data for individual schools. Some data are for the same schools under different conditions such as pre
and post-radon mitigation. In quite a few studies, investigators found a statistically significant partial correlation
between symptoms of headaches, dizziness, heavy headed, tiredness, difficulties concentrating, unpleasant odor,
and high CO2 concentrations (1500 - 4000 ppm compared to concentrations below 1500 ppm). Health symptoms
characterized as “irritations of the upper airways” were also higher at higher CO2 concentrations (p = 0.024).
Reduced performance on the Swedish Performance Evaluation System test was also observed at higher concen-
trations of CO2 [20] [21].
Turk, et al. reported ventilation measurements made in 6 non-complaint schools in the U.S. Northwest-2 in
Portland, Oregon and 4 in Spokane, WA. Schools ranged from 3 - 25 years in age, 1 - 3 stories; all had mechan-
ical ventilation systems of some type. Ventilation rates, calculated on a whole building volume basis, ranged
from 4.5 L/s-person to 31 L/s-person. The whole or average building rate, however, included unoccupied areas
such as hallways and gymnasiums, and, as the authors pointed out that the average rate overestimated the local
ventilation rate of occupied classrooms. For example, in one of the elementary schools, the whole building ven-
tilation rate was 4.5 L/s person while the ventilation rate in an occupied classroom was only 1.6 L/s-person [22]
[23].
Koskinen, et al. compared respiratory symptoms and infections in children (3 - 7 years old) in two daycare
centers with visible mold growth on interior walls (exposed children) to those in two reference daycare centers
(non exposed children). Parents recorded their children’s (N = 229) health symptom status in diary question-
naires during two study periods. During the first period, the children in the two daycare centers with mold prob-
lems (exposed) had a significantly increased risk of sore throat, purulent and non-purulent nasal discharge, nasal
congestion, hoarseness and common cold than those in the two reference daycare centers (non-exposed). During
the second follow-up period, a significantly increased risk of purulent nasal discharge, nasal congestion,
hoarseness and cough was observed for the exposed populations compared to the unexposed. Overall morbidity
for respiratory symptoms and common cold were higher in the daycare centers with the mold than in the two
reference day care centers [24].
Sometimes, the presence of both indoor contaminants and other indoor environmental factors makes it diffi-
cult to identify direct causes of occupant discomfort and health symptoms. Ventilation surrogates the Indoor Air
Quality (IAQ) level, minimizing the concentration of harmful pollutant. The higher ventilation rates are asso-
ciated with improved health. On the other hand, the health indicators are also very much depended upon the ex-
posure to indoor air pollutants.
Improvement of ventilation in living environment is always inevitable for health. Though ventilation models
are not generally considered as an exact exposure models, yet they are suitable for predicting indoor pollutant
exposure concentrations arising from specific sources. If full ranges and distributions of the input data are
available in indoor rooms or homes in a suburb, ventilation models can be run for probabilistic simulation of the
whole range of indoor exposure concentrations for the target population [25].
While progressing towards exposure model development through the measurement of ventilation rate in
household level, one has to consider the recognized contributing factors that create problems in indoor air quali-
ty followed by adverse health effects. Thus, exposure model is important in indoor environment because people
spend a substantial proportion of their time at home. In order to assess the total air exposure, it is crucial to take
into account of both the indoor and outdoor exposures. Most of the people spend majority of their life in indoors.
It means that the indoor pollution levels can substantially influence the total air exposure level. In indoor envi-
ronments, tobacco smoke and combustion of solid fuels for cooking and heating are the most significant sources.
In addition, construction material, furniture, carpeting, air conditioning, and home cleaning agents and insecti-
cides can also be significant sources of chemical and biological indoor-pollutants. It has been estimated that ap-
proximately half the world’s population, and up to 90% of rural households in developing countries, still rely on
biomass fuels. Although the portion of global energy derived from biofuel has fallen from 50% in 1900 to
K. Mukhopadhyay et al.
38
around 13% currently, this trend has leveled and there is evidence that biofuel use is increasing among the poor
[26]. For this class of people, a dual impact of simple awareness on ventilation and cost effective measurements
can reduce down the exposure arising out from the biomass fuel use, and would be more effective for women
and children.
Household characteristics with poor ventilating rooms might correlate strongly between the exposure to air
pollution and continuous usage of biomass fuel. Biomass fuel refers to any plant or animal based material deli-
berately burned by humans. Wood is the most common biomass fuel, but use of animal dung and crop residues
is also widespread. It may have some economical favours while the cooking is done for joint family members
with its cheap available sources. In most of the cases, these fuels are burned indoors in a traditional mud and, or
brick made chulhas (A U-shaped construction for cooking), which burn these fuels inefficiently and are often
not vented with flues or hoods to take the pollutants to the outside. Animal dung is on the lowest rung of the
ladder progressing to crop residues, wood, charcoal, kerosene, gas, and finally electricity. People generally
move up the ladder as socio-economic conditions improve.
Other sources of indoor air pollution in developing countries include smoke entering the home from nearby
houses, burning of forests, agricultural land and household waste, the use of kerosene lamps, and industrial and
vehicle pollution. This scenario of polluted indoor environment is known from the decade past, but the signifi-
cant change in exposure situation is still challenging due to poor socioeconomic condition, lack of awareness to
exposure, traditional mindset and poor administrative intervention with respect to exposure control. Many ef-
forts to address air pollution have done little to alleviate its total impact. In such situation, in spite of looking in-
to the emission source profile alone, equal importance has to be given to change the physical environment of the
households where establishment of the ventilation index may play a vital role to develop exposure model for as-
sessing indoor air quality without air monitoring complexities [27].
Fresh air is inevitable to all types of inhabitants in urban and rural settings and the requirement for air is rela-
tively constant about 10 - 20 m3 per day [28]. There is also a risk of droplet infection and lowered resistance to
diseases on prolonged exposure. The assumption that the outdoor air is ‘clean’ from a scientific point of view
surely not true but it is a fact that the rural air is in many places still of a rather good quality, which allows for
most cases to assume that such outdoor air is indeed ‘clean’. However, this is surely not the case for specific ap-
plications and for certain groups of the population sensitive to allergic reactions.
Ventilation influences in various ways the amount of indoor and outdoor air exposure. Optimum control of
the air change rate is therefore important. However, there is a clear lack of precise and scientifically well argued
target values in relation to the air pollution levels and, therefore also of the ventilation levels. Ventilation is the
supply and removal of air by either passive means—where air movement is driven by wind and temperature dif-
ferences through openings such as windows; or by active means—where the air is supplied and/or extracted by
mechanical methods such as ducts and fans. Ventilation is required for two separate functions: a) In cold weath-
er—to provide air for breathing and to provide fresh air to maintain IAQ; b) In warm weather—to provide air for
breathing, to maintain IAQ and to provide air movement for thermal comfort.
Ventilation in cold weather requires well-controlled air movement to meet the minimum needs of air quality
and comfort. Excessive ventilation can lower the temperature. The rate at which oxygen is consumed and CO2 is
produced rises rapidly with increased activity. The required rate of ventilation, therefore, rises with more vigor-
ous activities. For warm weather, ventilation from outside will only cool a space if the outside air is cooler than
the inside air. In some warmer areas, it will be warmer outside than inside. It is not just the temperature of the air
that cools us. Air movement lowers the perceived temperature, cooling us by evaporating our sweat. In warm
weather we need to maintain a steady flow of air for comfort. Air movement can be caused by wind, natural
convection—hot air rises and active (mechanical) means e.g., fans. Wind pressures are positive (push) on the
windward side of the building and negative (suck) on the leeward side. This encourages good cross-ventilation
in rooms with windows on opposite sides. Cross-ventilation must be carefully controlled to prevent too much air
movement in windy conditions. Wind cannot move the air through a room when there are only windows on one
side. Winds can have an effect on air changes in rooms up to eight meters deep, depending on wind strength.
However, effective ventilation may only be possible in shallower rooms i.e., no deeper than 2.5 times the ceiling
height. All the aforesaid parameters discussed are inevitable spices for making exposure model.
Mechanical ventilation is basically a method of delivering fresh air to the space using fans and ducts. The
concentration of CO2 in a room is often used as a guide to the quality of indoor air. Indoor concentrations above
about 1000 parts per million (ppm) CO2 indicate that IAQ is unacceptable. Humidity is an important factor in
K. Mukhopadhyay et al.
39
controlling thermal comfort and air quality. In buildings when the relative humidity is high and surface temper-
atures are low, condensation forms on the surfaces. The moisture from the air turns into water. Condensation is
more obvious on cold surfaces like glass, but is not always so noticeable on plasterboard walls. In July 2005, an
indoor air quality field study entitled “Ventilation and Indoor Air Quality in New Homes” was conducted in
USA to assist in answering some of the questions regarding ventilation and indoor air quality in new sin-
gle‐family detached homes. This field studies involved 108 new single‐family homes from Northern and South-
ern California, including a subset of 26 homes with mechanical outdoor‐air ventilation systems. The field teams
measured home ventilation and indoor contaminant source characteristics, including the amount of composite
wood associated with cabinetry/furnishings and the finishes of floors, walls, and ceilings; indoor contaminant
concentrations; the residents’ ventilation practices; IAQ perceptions; and decision factors regarding ventilation
and IAQ‐related actions. Measurements of indoor and outdoor air quality and ventilation parameters were made
in the summer, fall, and winter. Indoor air concentrations of volatile organic compounds; aldehydes (including
formaldehyde); PM2.5 particulate matter; nitrogen dioxide; carbon monoxide; carbon dioxide; temperature; and
relative humidity were measured over 24‐hour period. The outdoor air ventilation rates were determined con-
current with the air contaminant measurements using passive perfluoro carbon tracer (PFT) gas measurements.
In addition, the field teams measured the building envelope air leakage, garage‐to‐home air leakage, forced air
unit duct leakage, window use, airflow rates, and fan system usage. Twenty of the 108 homes were tested in
both the summer and winter seasons, and four homes were tested in the summer, fall, and winter. Four homes
were tested over multiple days, including weekends. This study provides, for the first time, statewide, accurate
and current information on both ventilation and IAQ in new California homes. Indoor air quality and household
ventilation practices were obtained from multiple seasons and regions of the state, which helped characterizing
the full range of indoor air contaminant exposure in such homes. Measured levels of ventilation and IAQ were
compared to current guidelines and standards. Information on the use of windows, fans, and central systems
helped establishing realistic values for developing California building energy efficiency standards. The Energy
Commission used the study results as a scientific basis to revise the state’s building energy efficiency standards,
in order to provide more healthful, energy‐efficient homes in California [29].
Cheng K. C. et al. conducted a study on modeling exposure close to an indoor air pollution source. An iso-
tropic turbulent diffusion coefficient was used to represent the average spread of emissions. However, its mag-
nitude indoors was difficult to assess experimentally due to limitations in the number of monitors available. A
number of real-time monitors were used to simultaneously measure CO at different angles and distances from a
continuous indoor point source. For 11 experiments involving two houses, with natural ventilation conditions
ranging from <0.2 to >5 air changes per h, an eddy diffusion model was used to estimate the turbulent diffusion
coefficients, which ranged from 0.001 to 0.013 m2∙s−1. The model reproduced observed concentrations with rea-
sonable accuracy over radial distances of 0.25 - 5.0 m. The air change rate, as measured using a SF6 tracer gas
release, showed a significant positive linear correlation with the air mixing rate, defined as the turbulent diffu-
sion coefficient divided by a squared length scale representing the room size [30].
Breen M. S. et al. published an overview and critical analysis of the scientific literature on empirical and
physically based AER models for residential and commercial buildings; the models highlighted here are feasible
for exposure assessments as extensive inputs are not required. Models are included for the three types of air-
flows that can occur across building envelopes: leakage, natural ventilation, and mechanical ventilation. Guid-
ance is provided to select the preferable AER model based on available data, desired temporal resolution, types
of airflows, and types of buildings included in the exposure assessment. For exposure assessments with some
limited building leakage or AER measurements, strategies are described to reduce AER model uncertainty [31].
In Guatemala, use of wood as a fuel source was associated with an adjusted 63-g lower birth weight (BW)
compared with electricity or gas, and in Zimbabwe use of high-pollution fuel (wood, dung or straw) was asso-
ciated with an adjusted 175-g lower BW compared with low-pollution fuel sources. A 104.5-g lower mean BW
was observed after adjusting for confounding factors in a population with 430% of babies born with weight <
2500 g [32] [33].
However, none of the articles published in the area of ventilation and exposure has been found to have strong
opinion for implementing ventilation protocol in residential households. A study by James M. Tielsch et al. [34]
revealed that the indoor particulate and gaseous exposures resulting from the use of biomass fuel sources at
home are associated with significant adverse health effects on the fetus and young infant including poor intra-
uterine growth (IUG), excess respiratory morbidity, poor postpartum growth and increased early infant mortality,
K. Mukhopadhyay et al.
40
although the strength of evidence for the mortality association was only modest. Likewise, so many publications
revealed the association between indoor particulates and respiratory health outcomes for the dwellers.
For attaining better air quality, improvement of room ventilation has been plasticized to be more convenient
and feasible for most of the residential households in the world. But, for growing concern of health effects due
to degraded indoor air, periodic checkup of air quality has become an important challenge for all of us. An al-
ternate cost-effective semi-quantitative way of estimating indoor air pollution has become a longstanding de-
mand among scientific communities as well. In this context, using room index and indoor ventilation data along
with a few meteorological parameters like temperature, relative humidity, wind direction etc. may play a crucial
role in validating association between ventilation and indoor air pollutants. The crucial part of this model is to
minutely observe changes of a specific pollutant concentration with respect to changing ventilation status in the
households. Once, the data set is validated with the available gold standard methods, it would be a control
banding approach for estimating indoor air pollution in many rural and urban households with equivalent room
space, temperature, relative humidity, number of residents and fuel source.
2. Conclusion
There is general consensus that a link exists between ventilation rates and concentration of air pollutants in in-
door environment which may subsequently correlate health outcomes. To reduce laboratory costs, and other
complexities of maintaining quality research in indoor environment, an innovative trial of assessing air pollu-
tants with simple ventilation status could be an important endeavor. Hence, it is expected that the use of ventila-
tion index in indoor environments may be one of the important control banding approaches in establishing ex-
posure model for indoor air pollution. If the ventilation rate followed by its index is used for the development of
exposure model, the time, labour and expenditure in indoor air monitoring research can be reduced drastically.
Acknowledgements
The authors express their sincere thanks to the Indian Council of Medical Research (ICMR) for providing a re-
search grant (ICMR-CAR) to the Department of Environmental Health Engineering, Sri Ramachandra Univer-
sity, Chennai, India and being associated in enormous number of indoor air assessment activities in the project,
the idea of this review work knocked the mind. As the scope of generating data for exposure model is still alive,
it is expected to be a wonderful model in near future concerning the association between ventilation index and
exposure outcomes in different household characteristics.
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