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Emissions from an International Airport Increase Particle Number Concentrations 4-fold at 10 km Downwind

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We measured the spatial pattern of particle number (PN) concentrations downwind from the Los Angeles International Airport (LAX) with an instrumented vehicle that enabled us to cover larger areas than allowed by traditional stationary measurements. LAX emissions adversely impacted air quality much farther than reported in previous airport studies. We measured at least a 2-fold increase in PN concentrations over unimpacted baseline PN concentrations during most hours of the day in an area of about 60 km(2) that extended to 16 km (10 miles) downwind and a 4- to 5-fold increase to 8-10 km (5-6 miles) downwind. Locations of maximum PN concentrations were aligned to eastern, downwind jet trajectories during prevailing westerly winds and to 8 km downwind concentrations exceeded 75 000 particles/cm(3), more than the average freeway PN concentration in Los Angeles. During infrequent northerly winds, the impact area remained large but shifted to south of the airport. The freeway length that would cause an impact equivalent to that measured in this study (i.e., PN concentration increases weighted by the area impacted) was estimated to be 280-790 km. The total freeway length in Los Angeles is 1500 km. These results suggest that airport emissions are a major source of PN in Los Angeles that are of the same general magnitude as the entire urban freeway network. They also indicate that the air quality impact areas of major airports may have been seriously underestimated.
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Emissions from an International Airport Increase Particle Number
Concentrations 4fold at 10 km Downwind
Neelakshi Hudda,
Tim Gould,
Kris Hartin,
§
Timothy V. Larson,
and Scott A. Fruin*
,,
Keck School of Medicine, Department of Preventive Medicine, University of Southern California, Los Angeles, California 90089,
United States
Department of Civil and Environmental Engineering, University of Washington, Seattle, Washington 98195, United States
§
Department of Environmental and Occupational Health Sciences, University of Washington, Seattle, Washington 98195, United
States
*
SSupporting Information
ABSTRACT: We measured the spatial pattern of particle number (PN)
concentrations downwind from the Los Angeles International Airport
(LAX) with an instrumented vehicle that enabled us to cover larger areas
than allowed by traditional stationary measurements. LAX emissions
adversely impacted air quality much farther than reported in previous
airport studies. We measured at least a 2-fold increase in PN
concentrations over unimpacted baseline PN concentrations during
most hours of the day in an area of about 60 km2that extended to 16 km
(10 miles) downwind and a 4- to 5-fold increase to 810 km (56
miles) downwind. Locations of maximum PN concentrations were
aligned to eastern, downwind jet trajectories during prevailing westerly
winds and to 8 km downwind concentrations exceeded 75 000 particles/
cm3, more than the average freeway PN concentration in Los Angeles.
During infrequent northerly winds, the impact area remained large but shifted to south of the airport. The freeway length that
would cause an impact equivalent to that measured in this study (i.e., PN concentration increases weighted by the area impacted)
was estimated to be 280790 km. The total freeway length in Los Angeles is 1500 km. These results suggest that airport
emissions are a major source of PN in Los Angeles that are of the same general magnitude as the entire urban freeway network.
They also indicate that the air quality impact areas of major airports may have been seriously underestimated.
INTRODUCTION
Previous studies that directly measured the impact of aviation
activity on air quality have mostly conducted measurements in
close proximity of airports. Few studies have reported
signicant air quality impacts extending beyond a
kilometer.
14
Carslaw et al. 2006
1
analyzed dierences in
pollutant concentrations by wind speed and direction along
with dierences in aircraft and ground trac activity at
Heathrow Airport in London. They found airport contributions
of up to 15% of total oxides of nitrogen (NOx) at a site 1.5 km
downwind of the nearest runway. At Hong Kong International
Airport, Yu et al. 2004
2
used nonparametric regression analysis
on pollutant concentrations by wind speed and direction. They
calculated that aircraft nearly doubled sulfur dioxide concen-
trations 3 km away and also increased concentrations of carbon
monoxide and respirable suspended particles under similar
wind speeds and directions. Fanning et al. 2007
3
measured
particle numbers concentrations in the 10100 nm range and
found signicant increases above background at 1.9, 2.7, and 3.3
km downwind of the Los Angeles International Airport (LAX)
blast fence. Although measurements were stationary and not
concurrent, they also noted that takeos produced high
concentrations and downwind gradients within 600 m of the
blast fence. Dodson et al. 2009
4
found that aircraft activity at a
regional airport in Warwick, RI contributed 2428% of the
total black carbon (BC) measured at ve sites 0.163.7 km
from the airport.
Several other airport and aviation emissions studies focused
on quantifying the air quality impacts from jet takeos
5,6
and
measured air pollutant concentrations very close to runways. Of
particular relevance to this study, Hsu et al. 2013
7
linked ight
activity at LAX with 1 min average PN concentrations. Their
models suggested that aircraft produced a median PN
concentration of nearly 150 000 particles/cm3at the end of
the departure runway. PN concentrations decreased rapidly
with distance to 19 000 particles/cm3at a location 250 m
downwind and to 17 000 particles/cm3at a location 500 m
further downwind. The rapid drop-oin concentration,
however, may have reected an increasing oset from the
centerline of impacts with greater downwind measurement
distance. Similar magnitude PN concentrations and correlations
Received: January 22, 2014
Revised: May 12, 2014
Accepted: May 14, 2014
Published: May 29, 2014
Article
pubs.acs.org/est
© 2014 American Chemical Society 6628 dx.doi.org/10.1021/es5001566 |Environ. Sci. Technol. 2014, 48, 66286635
Terms of Use
with departures were reported by Westerdahl et al. 2008
8
and
Zhu et al. 2011
9
at sites located within 100200 m of the Hsu
et al. 2013
7
measurements.
Our study was motivated by mobile monitoring platform
(MMP) based observations of large but gradual increases in PN
concentrations as we approached locations under LAX jet
landing trajectories on multiple transects up to 10 km
downwind of LAX. We hypothesized that emissions from
LAX activities were increasing PN concentrations over much
larger areas and longer downwind distances than previously
observed in studies that focused on near freeway and jet takeo
impacts to air quality. An extensive monitoring campaign
conrmed that LAX-related emissions increased PN concen-
trations downwind at least 2-fold to 16 km. This large,
previously undiscovered spatial extent of the air quality impacts
downwind of major airports may mean a signicant fraction of
urban dwellers living near airports likely receive most of their
outdoor PN exposure from airports rather than roadway trac.
MATERIALS AND METHODS
Monitoring Area. LAX is the sixth busiest airport in the
world and third busiest in the United States. About 95% of
ights take oand land into the prevailing westerly/west-
southwesterly (W/WSW) onshore winds
10
(i.e., 263 degrees,
the direction of runway alignment
2
) using two sets of parallel
runways separated by about 1.5 km. In the busiest hours, 40
60 jets per hour arrive during hours 07001900 and depart
during hours 08002100. Reduced activity is typical for the
early morning and late evening hours. 2040 jets per hour
arrive during hours 0600 and 10000100 and depart during
hours 0700 and 22002300. During other hours typically fewer
than ve jets per hour arrive or depart.
10
The airport complex is about 4.5 km east to west (E-W) and
about 2.5 km north to south (NS) and is surrounded by
major roadways and freeways, as highlighted in Figure 1 (Figure
S.1 in Supporting Information (SI) shows a map of this area
with street name labels). The Federal Aviation Administration
noise contours of the modeled annual 65 dB A-weighted
equivalent (LAeq) noise threshold are shown
11
extending
eastward along the predominant downwind direction and
reect the jet trajectories used for landing. They also extend
west of the airport over the Pacic Ocean (not shown).
Mobile Monitoring. Monitoring consisted of transects 4
16 km in length, nearly perpendicular (i.e., NS) to the
direction of the prevailing winds, at varying downwind
distances. Dierent monitoring routes were required to fully
capture the changes in impact locations due to shifts in wind
direction. A general downwind direction was chosen based on
meteorological predictions but transect lengths and locations
were determined during the monitoring run based on
observations of the rate of change of PN concentrations. For
each transect, monitoring was extended several hundred meters
beyond the location where baseline PN concentrations
appeared stable.
Measurements were conducted over 29 days with the
University of Southern California (USC) MMP, a gasoline-
powered hybrid vehicle. A second MMP, the University of
Washington (UW) MMP, a gasoline-powered minivan, joined
the monitoring on 3 days (June 22, 27 and July 1, 2013). Table
1 gives monitoring dates and times.
Most measurements were conducted during times of onshore
westerly winds, typically strongest during 11001600, but we
also conducted measurements during early morning and late
night hours when air trac was low and onshore winds were
reduced (August 13, 16, 23, 24 and 25, December 03, 09, 15
and 16, 2013). Monitoring focused on the area east of LAX
(i.e., the predominant downwind direction) but included
several runs along the boundary of the airport in the upwind
direction and south of the airport complex during occasions of
northerly winds in winter months.
Instrumentation. Concentration measurements included
PN, BC, NO, NO2, NOx,and particle surface UV-photo-
ionization potential (measured using Ecochem Photoelectric
Aerosol Sensor [PAS] that responds to elemental carbon and
particle-bound polycyclic aromatic hydrocarbons [PBPAH]).
Instrument details are provided in SI (Table S.1 and S.2).
Instruments were powered by two deep-cycle marine batteries
via DC-to-AC inverter. Our power arrangement allowed for 5 h
of run time if all instruments were running. For sampling runs
that were anticipated to exceed 5 h, several instruments were
shut down to extend battery life and the Condensation Particle
Counter (CPC) was run on the vehicles 12 V cell phone power
outlet. If other instruments were turned on later, the required
warm-up time was 25 min.
Instrument clock times were regularly synchronized to be
within 1 s of the global positioning system device time, which
also recorded speed and location. Measurements from
instruments with a delayed response time were advanced to
match the instantaneous instruments and the GPS time and
location recorded at 1 s intervals. For pollutant measurements
recorded at 10 s intervals, all locations within the recording
interval were assigned the pollutant value reported for that
interval.
Meteorological Data. Minute and hourly wind speed and
wind direction data were obtained from the Automated Surface
Observing Systems monitor at LAX airport (latitude 33.943
and longitude 118.407). Due to the 16 km distance between
eastern edge of the study area and the meteorological station
located at LAX, we could not assume that wind speed and
direction were identical to those measured at LAX, but wind
direction in this region of Los Angeles tends to be similar over
large areas during daytime.
12
The average wind direction at LAX is WSW (252°).
12
Daytime southwesterly sea breezes typically occur 16 h per day
in the summer (09000100 for JuneAugust), decreasing to 6
Figure 1. Los Angeles International Airport and 65 dB noise contours
indicating eastern jet trajectories.
Environmental Science & Technology Article
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h in the winter (12001800 in December). Only during the
winter months (NovemberFebruary, 00000900) are light
easterly o-shore winds common.
12
Wind speed and direction
during the monitoring periods are summarized in Table 1.
Wind roses based on 1 min data are shown in Figure S.2 and
S.3 of the SI.
Data Processing. MMP measurements included a localized
trac emissions signal representing microscale and middle scale
variations (10100 m and 100500 m, respectively) and an
underlying baselinepollutant concentration that varied
gradually over the neighborhood scale (500 m4 km).
13
Watson et al. 1997
13
derived these categories by considering
the spatial scales of impact of various types of air pollution
sources. We adopted a smoothing methodology to estimate
baseline PN concentrations that excluded the microscale and
middle scale impacts due to local sources, usually specic
vehicles.
Baseline PN concentrations were derived from our mobile
measurements by taking a rolling 30-s fth percentile value of
the 1-s concentration time series, and assigning that value to the
measured location. This removed the microscale and middle
scale impacts from trac sources such as specic vehicle
plumes. Baseline concentrations for a run were relatively
spatially uniform outside of the LAX impact areas, with
coecients of variation (CV) of less than 5%. In comparison,
the raw PN concentrations on roadways outside the LAX
impact areas had CVs on the order of 40%. On rare occasions,
the MMP was behind a high emitter for longer than 30 s. Such
events, only if veriable by video and eld notes, were censored.
However, less than 0.5% of data were censored in this manner,
generated from about a dozen instances of prolonged inuence
from high emitting vehicles. An illustration of both raw and
smoothed concentration time series is presented in the SI
(Figures S.4S.7). The gures in this text are based on
smoothed data.
RESULTS AND DISCUSSION
Spatial Pattern and Extent of Elevated PN Concen-
trations. Downwind of LAX we observed gradual but large
increases in baseline PN concentrations occurring over transect
distances of multiple kilometers. PN concentrations were
elevated 4-fold or more above nearby unimpacted baseline
concentrations up to 10 km in the downwind direction from
Table 1. Sampling Days, Time Periods and Meteorological Conditions during Sampling
date
a
time sampling distance
from LAX (km) WD
b
WS (m/s)
urban
background
PN
c
ratio of impacted to unimpacted
baseline PN, 10 km downwind
4/6/2011 14:3016:45 812 WSW, W5.0 ±1.8 15 000 2.0
4/10/2011 15:0017:30 812 W6.9 ±1.2 10 000 4.5
5/24/2011 09:0011:00 812 Calm, W 1.0 ±2.5 10 000 3.0
5/27/2011 12:1514:45 812 WSW, W6.3 ±1.3 10 000 4.7
1/26/2012 17:2820:22 812 WSW, W2.9 ±2.1 20 000 6.0
9/29/2012 13:3017:30 08W6.1 ±1.1 10 000 3.7
9/30/2012 15:4518:30 08W6.1 ±0.4 5000 5.2
6/11/2013 14:1415:14 2.58.5 WSW, W 6.7 ±0.0 15 000 5.0
6/12/2013 13:3016:30 2.510.5 W4.0 ±0.4 15 000 4.0
6/22/2013 11:4718:50
d
08 WSW, W5.7 ±0.4 10 000 4.4
6/27/2013 11:4918:00
d
08 WSW, W5.3 ±0.7 10 000 4.0
7/01/2013 10:3018:30
d
08W, ESE 3.8 ±1.0 15 000 3.8
e
8/6,7/2013 23:5602:45 08 WSW, W, S 3.3 ±0.7 10 000 3.3
8/13/2013 06:3015:00 08 Calm, WSW, W, NNE, NE,
ENE, E, ESE
f
3.0 ±2.0 10 000 4.0
8/15/2013 08:3015:30 016 Calm, WSW,W2.5 ±2.1 20 000 3.8
8/16/2013 09:4520:50 016 SW, WSW,W, WNW 4.4 ±1.3 10 000 3.0
8/23,24/2013 12:0001:30 016 SSW, WSW,W4.4 ±2.2 20 000 4.0, 5.0
8/24,25/2013
g
17:3001:00 016 Calm, SSW, SW, WSW,W,
ESE 3.1 ±2.1 15 000 6.0
11/1/2013 16:0019:50 012 SSE, W, WSW 3.7 ±0.7 10 000 3.8
e
12/3/2013 19:4500:20 012 WSW, W, WNW 8.8 ±1.4 5000 6.0
12/5/2013 13:0018:30 012 WSW, W, WNW 5.5 ±0.6 10 000 2.8
12/9/2013 16:0000:00 010 N, NNE 2.7 ±0.6 20 000 n/a
12/10/2013 15:3021:30 010 WNW,N, NW 3.1 ±1.1 20 000 5.0
12/14/2013 17:0020:30 010 W, Calm 2.1 ±0.5 20 000 data lost
12/15,16/2013 22:0002:00 010 N, NE, ESE 2.9 ±1.0 17 500 n/a
12/16/2013 10:0016:00 012 N, W 2.8 ±1.6 10 000 4.5
12/18/2013 17:3020:30 010 WSW, SSW, SSE 3.3 ±1.3 10 000 6.0
12/20/2013 16:3020:00 010 WSW, Calm, E 2.6 ±1.3 15 000 4.0
12/23/2013 15:1519:00 012 W, Calm, E 2.8 ±1.3 10 000 11.0
a
The runs for which maps are presented are formatted in bold.
b
Predominant wind direction is formatted as bold.
c
Urban background value
concentrations are reported to nearest 2500 particles/cm3and are the average baseline values in the unimpacted areas away from local trac sources
d
Concurrent MMP sampling times: June 22:13201720, June 27:13251510, July 1:12401640.
e
Monitoring route did not cover the full NS
extent of the impact on Western Av (10 km downwind) on these days, values have been reported for Crenshaw Blvd. (8 km downwind).
f
Easterly
ow was recorded in morning hours (until 1000) and westerly later morning to afternoon
g
08/25/2013 was not counted as an additional monitoring
day because only 1 h of monitoring (00000100) was conducted on this date
Environmental Science & Technology Article
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LAX. Figure 2 shows an example of the spatial pattern of the
elevated PN concentrations.
The size of the impacted areas with high PN concentration
increases was remarkable. At 16 km downwind, a 2-fold
increase in PN concentration over baseline concentrations was
measured across 6.5 km. Assuming a trapezoidal shaped plume
with parallel edges of length 1.5 and 6.5 km, PN concentrations
were at least doubled over an area of 60 km2. Eight km
downwind, a 5-fold increase in PN concentrations over baseline
concentrations extended across 3 km and covered a total area of
24 km2. (Concentrations in this large area exceeded 71 000
particles/cm3, the average concentration on Los Angeles
freeways.
14
) Within 3 km of the airport boundary, concen-
trations were elevated nearly 10-fold, exceeding 100 000
particles/cm3, with concentrations of 150 000 particles/cm3
occurring over a several km2area.
This pattern of elevated PN concentrations over large areas
east of LAX was consistently observed during periods when
there were both westerly winds and high air trac volumes,
typically all daylight hours and well into the night. Figure 3
Figure 2. Spatial pattern of PN concentration (colored by deciles) for
the afternoon and evening hours of August 23, 2013.
Figure 3. Spatial pattern of impact during dierent monitoring events. Wind direction during monitoring is shown in insets on bottom left. PN
concentrations are classied and colored by deciles.
Environmental Science & Technology Article
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shows the consistency of the patterns over eight monitoring
runs at various times of day, displayed in each row by similarity
of spatial scale.
In directions other than the downwind direction, no large
areas of elevated PN concentrations were observed. Figures
3(c)(e) include concentrations measured upwind of the LAX
boundary (these are indicated by faint yellow lines within the
noise contour); the concentrations recorded were typical of the
coastal baseline concentrations, less than 10 000 particles per
cm3(also see Figure S.8 in SI). Of possible other PN sources, a
large renery is located south of the airport but we did not
observe elevated PN or other pollutant concentrations directly
downwind of this source. In general, industrial point sources of
pollution in the Los Angeles Air Basin are very tightly regulated
by the South Coast Air Quality Management District.
We did not observe distinct day versus night dierences, as
might be expected based on the large change in meteorolog-
ically driven dilution between day and night for ground level
sources. It appeared that the distant impacts we observed
downwind of LAX required sucient wind speeds for the jet
climbing and landing emissions to reach the ground, as
observed in Yu et al., 2004
2
at LAX and Hong Kong
International Airports and Carslaw et al. 2006
1
at Heathrow
Airport. At LAX, this probably corresponded to the develop-
ment of the on-shore sea breezes that typically started 46h
after sunrise and lasted until 36 h after sunset.
12
We also did not see the impacts of individual jets at the
distances monitored, but the merging of individual jet impacts
is not unexpected at distances of multiple km. Considering the
frequency of landings and takeos (>90 per hour from 0900
2100
10
), at an average wind speed of 4 m/s, for example, an
incoming parcel of air will travel only about 160 m before
another jet landing or takeooccurs. Under normal daytime air
turbulence and the enhanced turbulence produced by jets,
15,16
signicant mixing is expected over a 510 km distance (2040
min). The generally smooth increases and decreases observed
across the length of transects at such distances are additional
evidence that mixing of plumes occurs. Examples of these
smooth concentration increases for individual transects are
shown in Figures S.6 and S.7 in the SI.
The consistent and distinctive spatial pattern of elevated
concentrations was aligned to prevailing westerly winds and
landing jet trajectories, and roughly followed the shape of the
contours of noise from landing jets, indicating that landing jets
probably are an important contributor to the large downwind
spatial extent of elevated PN concentrations. As dened by the
International Civil Aviation Organization, typical engine thrust
during landing is 30%, as compared to 100% for takeoand
85% for the climbing phase.
6
Stettler et al. 2011
6
calculated
18% of total NOxemissions from landings, with 12% from
taxiing and holding, 18% from takeo, and 52% from the climb
and climb out phases, respectively. When the extra upwind
distance of the climb and climb out phases are taken into
account, the landing approach emissions likely produce a
signicant fraction of the increased PN concentrations observed
downwind.
Inuence of Wind Direction on Location of Impact.
The downwind location of the impact changed with shifts in
the prevailing wind direction, although signicant shifts in wind
direction during the daytime are not typical of this area of Los
Angeles.
12
Figure 4(a) and (b) illustrate one such change in
impacted locations due to a shift in wind direction on a gusty
day with frontal weather that also resulted in cleaner upwind
baseline PN concentrations of less than 5000 particles/cm3.
The impacted locations were aligned along the NE direction
during 20002220 h when winds were from W to WSW (250
280°). The impact then moved southwards between 2220
0000 h as winds turned more W to WNW (280330°). During
this shift, the impact centerline moved by 5.5 km on transects
810 km east of LAX.
Monitoring was also conducted during N to NE prevailing
winds that tend to occur late at night in November and
December (21002300).
12
This N to NE wind direction
resulted in impacts that were centered south of the airport
(Figure 4(c)). The PN concentrations in this southerly impact
were roughly twice as high as on other days, in part because the
baseline PN concentrations reected urban air from northerly
winds instead of marine air from westerly winds.
Diurnal wind patterns change little by season in Los Angeles
basin.
12
Onshore westerly winds are common during midday
hours, even in winter. As a result, areas of elevated PN
Figure 4. Change in location of impact due to shift in wind direction. Wind direction during monitoring is shown in insets on bottom left. PN
concentrations are classied and colored by deciles.
Environmental Science & Technology Article
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concentrations downwind and east of LAX likely occur in all
seasons. Monitoring in dierent seasons demonstrated the
consistent year round presence of this impact. Examples of
similarly extensive impacts in non-summer months are shown
in the SI (Figures S.8 and S.9).
Other Pollutants. Over large areas downwind of LAX,
concentrations of pollutants other than PN were also elevated.
Figure 5(a)(c) show nearly indistinguishable spatial patterns
for PN, BC, and NO2concentration measured simultaneously
at distances of 9.512 km from LAX. This suggests a common
source for these pollutants, although the BC concentration
increases were not large when compared to PN and NOx, about
0.51μg/m3at 810 km downwind. While jet aircraft are not
known to produce large amounts of BC, two studies found
elevated BC from plane takeos at LAX. Zhu et al. 2011
9
measured an increase of about 1 μg/m3of BC due to plane
activity 140 m downwind of the runway. Westerdahl et al.
2008
8
measured increases in BC concentration of several μg/
m3during takeoevents near the eastern LAX boundary, but
also observed elevated BC concentrations at all times. At a
smaller airport, Dodson et al. 2009
4
found median contribu-
tions of about 0.1 μg/m3, about one-quarter of total BC
measured at ve sites ranging in downwind distance from
0.33.7 km, and also observed departures producing about
twice the impact as arrivals. Therefore, it appears some jets at
LAX are capable of producing measurable increases in BC,
particularly at takeos.
Spatial patterns of simultaneously measured PN and PAS
response (PBPAH and EC) were also similar on transects
4.57.5 km from LAX (Figure 5(d)(e)). The NOXelevation
pattern was less regular (Figure 5(f)). This was likely due to
smaller LAX related contributions compared to baseline
concentrations, thus reducing the signal-to-noise ratio.
Figure 5. Spatial pattern of simultaneously measured pollutants during 14001530 on June 27, 2013. Concentrations are classied and colored by
deciles. Panels (a)(c) show data measured by the UW MMP and (d)(f) show data measured by the USC MMP.
Figure 6. Comparison of the spatial scale of freeway impacts compared to airport impacts for monitoring during nighttime on August 2324, 2013.
Environmental Science & Technology Article
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Overall, the top quartile concentrations (highly impacted) of
all pollutants were about three times higher than the lowest
quartile within 7.5 km from LAX and two times higher at 12 km
distance. In addition, concurrent sampling with the two mobile
platforms demonstrated high temporal (SI Figure S.10) and
spatial consistency (SI Figure S.11) for PN measurements.
Comparison of LAX and Freeway PN Impacts. PN
concentration increases from ground level line sources such as
freeways, under conditions of daytime crosswind dilution,
decrease exponentially with increasing downwind distance and
return to baseline concentrations within 200300 m.
17
The
two NS freeways (I-405 and I-110 that run perpendicular to
the prevailing winds) did not contribute appreciably to elevated
PN concentrations in areas where we observed large impacts
from LAX on PN concentrations. This is illustrated in Figure 6,
which contains two enlargements to show the increase in PN
number concentrations over approximately 250 m distance
downwind of I-405, a distance and an increase in PN
concentration that is not discernible at the scale of Figures 2
and 3. The panel in Figure 6(c) at 1:10 000 scale shows the PN
concentration increase of about 24 000/cm3. The maximum PN
concentration was not immediately downwind of the freeway
because at this location there is an elevated overpass and some
distance is needed for emissions to reach the ground.
To put into further perspective the extent of the elevated PN
concentrations observed downwind of LAX, we estimated the
freeway length necessary to produce an equivalent impact in
terms of PN concentration-weighted area of impact assuming
typical daytime dilution conditions for freeways.
For the days we captured the fullest downwind extent of the
impact under typical daytime wind conditions (August 15, 23,
and 24), we calculated an integrated PN impact above baseline
PN concentrations of 2.3, 1.6, and 1.1 ×106(particles/cm3)×
km2, respectively. See Table S.3(a)(c) of SI for calculations.
Impacted areas were calculated using ArcGIS spatial analysis
tools and were conservatively dened as areas where increased
PN concentration were at least double the baseline
concentrations measured north and south of the impact zone.
The resulting impact areas were 3065 km2. For comparison, a
less conservative criterion for dening the impact area such as a
50% or 33% increase over baseline PN concentrations increased
the impacted area by 40% and 80%, respectively.
To calculate PN impacts downwind of freeways, we
combined the exponential regression t of near-freeway
measurements made downwind of I-405 by Zhu et al.
2002a
18
with updated average daytime on-freeway PN
concentrations taken from Li et al. 2013
14
(71 000 particles/
cm3). PN concentrations were at least double the baseline PN
concentrations of 15 00020 000 particles/cm3for 90130 m
downwind.
3
This resulted in a concentration-weighted impact
area of 29303930 (particles/cm3)×km2per km of freeway
length.
Based on these concentration-weighted impact areas, 280
790 km of freeway are needed to produce the equivalent PN-
concentration-weighted impact area of LAX. (The less
conservative criteria resulted in ranges of freeway length of
3401000 km and 4301100 km for thresholds of 50% and
33%, respectively.) There are only about 1500 km of freeways
and highways in Los Angeles County.
19
Therefore, LAX should
be considered one of the most important sources of PN in Los
Angeles. For comparison, within the 60 km2area of elevated
PN concentrations downwind and east of LAX, the 1525 km
of freeways contributed less than 5% of the PN concentration
increase.
Recommendations for Other Studies. LAX is in a region
of Los Angeles with highly consistent wind direction. This
provided the several hours necessary for a single mobile
platform to monitor a sucient number of transects to cover
the large area impacted by LAX emissions. At airport locations
where the prevailing wind direction frequently shifts during the
day, multiple platforms would be necessary to quickly capture
the full spatial extent of emissions impacts to surrounding air
quality.
The emissions from LAX are likely not unique on a per-
activity basis. The large area of impact from LAX suggests that
air pollution studies involving PN, localized roadway impacts,
or other sources whose impacts are in the inuence zone of a
large airport should carefully consider wind conditions and
whether measurements are inuenced by airport emissions.
Source apportionment of specic airport sources or activities
was beyond the scope of our study but would be necessary to
evaluate the eectiveness of possible mitigation options.
Diering NO2to NOxratios at dierent levels of engine
thrust
20
might be used to distinguish the contributions of jet
landing, idling or takeoactivities. Takeoand idling emission
also dier in surface properties (i.e., the ratio of active surface
area to surface bound photoionizable species)
21
and particle
size distributions dier between aircraft and ground support
equipment emissions.
21
ASSOCIATED CONTENT
*
SSupporting Information
Map of monitoring area (Figure S.1), the instruments used
(Tables S.1S.2), wind roses (Figures S.2 and S.3), illustration
of data processing (Figures S.4S.7), additional maps
illustrating the spatial pattern (Figures S.8 and S.9), concurrent
sampling with two mobile measurement platforms (Figures
S.10 and S.11) and calculations for comparing freeway impact
(Table S.3 (a)(c)) are presented in the Supporting
Information. This material is available free of charge via the
Internet at http://pubs.acs.org.
AUTHOR INFORMATION
Corresponding Author
*Phone: 323-442-2870; fax: 323-442-3272; e-mail: fruin@usc.
edu.
Present Address
S.A.F.: Keck School of Medicine, Department of Preventive
Medicine, University of Southern California, 2001 North Soto
Street, Los Angeles, CA 90089-9013, United States.
Notes
The authors declare no competing nancial interest.
ACKNOWLEDGMENTS
This work was funded by National Institute of Environmental
Health Sciences (NIEHS) Grant 1K25ES019224-01 and
5P30ES007048 to the University of Southern California and
by US EPA Grant RD-83479601-0. This publications contents
are solely the responsibility of the grantee and do not
necessarily represent the ocial views of NIEHS or US EPA.
Further, NIEHS and U.S. EPA do not endorse the purchase of
any commercial products or services mentioned in the
publication. We thank Andrea Hricko of USC for helpful
comments.
Environmental Science & Technology Article
dx.doi.org/10.1021/es5001566 |Environ. Sci. Technol. 2014, 48, 662866356634
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Environmental Science & Technology Article
dx.doi.org/10.1021/es5001566 |Environ. Sci. Technol. 2014, 48, 662866356635
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Predictions as to the transport of aircraft NOx emissions to ground level in the vicinity of an airport are made, taking account of the vortical dynamics of the aircraft wake. A model is used to calculate mean ground-level concentrations. It employs a kinematic approach, harnessing results from dynamical models in the literature. Two aircraft types are considered, a B737-300 (twin turbofan), taken as representative of short-range aircraft, and a B747-400, taken as representative of long-range aircraft. Airport and meteorological parameters are assigned values as holding in the case of Manchester Airport, UK, during a fortnight in May 1999 (prior to the opening of a second runway there). The airport operated at a capacity of about 45 aircraft movements per hour in the peak morning period, with frequencies in the middle of the day being about half this. Aircraft of maximum takeoff weight in excess of 120tonnes accounted for some 6% of all movements. The simulations predict mean NOx concentrations of maximum 3μgm−3 at the centre of the runway arising as a result of the vortex-mediated transport (as expressed on conversion of all NO to NO2), with concentrations on the order of 1μgm−3 arising 0.5km laterally from the runway.
Article
An aircraft exerts a downward force on the air, so aircraft exhausts tend to descend toward the ground within the aircraft's wake. The wake of an aeroplane descends in an essentially inviscid and thus long-lived manner, through the action of a pair of trailing counterrotating vortices on one another. The vortices derive from the circulation about the wings yielding the lift. Exhaust pollutants may thus be conveyed to the ground close to airports, far more effectively than through ambient atmospheric dispersion alone, as has hitherto been assumed occurs within air-quality models. The presence of the vortices in the vicinity of airports is well-established, as it is the need to wait for their decay or movement out of the flight corridor—for the safety of the following aircraft—that caps departure and arrival rates at busy periods. The dynamics of the transport are elucidated, so that the impact of the transport on pollutant concentrations at ground level in an airport environs may be established.
Article
Background: While commercial aircraft are known sources of ultrafine particulate matter (UFP), the relationship between airport activity and local real-time UFP concentrations has not been quantified. Understanding these associations will facilitate interpretation of the exposure and health risk implications of UFP related to aviation emissions. Objectives: We used time-resolved UFP data along with flight activity and meteorological information to determine the contributions of aircraft departures and arrivals to UFP concentrations. Methods: Aircraft flight activity and near-field continuous UFP concentrations (≧ 6 nm) were measured at five monitoring sites over a 42-day field campaign at Los Angeles International Airport (LAX). We developed regression models of UFP concentrations as a function of time-lagged landing and take-off operations (LTO) activity, in the form of arrivals or departures weighted by engine-specific estimates of fuel consumption. Results: Our regression models demonstrate a strong association between departures and elevated total UFP concentrations at the end of the departure runway, with diminishing magnitude and time-lagged impacts with distance from the source. LTO activity contributed a median (95th, 99th percentile) UFP concentration of approximately 150,000 particles/cm(3) (2,000,000, 7,100,000) at a monitor at the end of the departure runway, versus 19,000 particles/cm(3) (80,000, 140,000), and 17,000 particles/cm(3) (50,000, 72,000) for monitors 250 m and 500 m further downwind, respectively. Conclusions: We demonstrated significant contributions from aircraft departure activities to UFP concentrations in close proximity to departure runways, with evidence of rapid plume evolution in the near field. Our methods can inform source attribution and interpretation of dispersion modeling outputs.