regional sources of particulate sulfate, so2, pm2.5, hcl, and hno3, in new york, ny
TRANSCRIPT
Atmospheric Environment 37 (2003) 2837–2844
Regional sources of particulate sulfate, SO2, PM2.5, HCl,and HNO3, in New York, NY
Abdul Baria, Vincent A. Dutkiewicza,b, Christopher D. Judda, Lloyd R. Wilsonc,Dan Luttingerc, Liaquat Husaina,b,*
aWadsworth Center for Laboratories and Research, New York State Department of Health, Albany, NY 12201-0509, USAbDepartment of Environmental Health and Toxicology, School of Public Health Sciences, State University of New York, Albany, USA
cNew York State Department of Health, Center for Environmental Health, 547 River Street, Troy, NY, USA
Received 2 June 2002; accepted 12 March 2003
Abstract
Simultaneous measurements of gaseous HONO, HNO3, HCl, SO2, and NH3 from July 1999 to June 2000 and fine-
fraction particulate (o2:5mm) sulfate and PM2.5 mass from January 1999 to November 2000 were made at Bronx and
Manhattan in New York City. Air trajectories were used to study the impact of upwind emissions on the observed
concentrations in New York City. Episodes of high concentrations of the chemical species were observed at both Bronx
and Manhattan throughout the year, although, they were more prominent during summer. The highest concentrations
were invariably associated with the air flow from southwest to west of New York City. Three-hour HYSPLIT4 air
trajectories were used to apportion the daily measured concentrations as a function of direction. On an annual basis
43% of sulfate, 14% of the sulfur dioxide, 30% of the PM2.5 mass, 27% of HCl, and 24% of HNO3 were attributed to
upwind emissions, with the remaining amounts due to emissions in the metropolitan New York.
r 2003 Elsevier Science Ltd. All rights reserved.
Keywords: Acidic gases; Annular denuder system; Air trajectories; Urban area; Ammonia; HONO
1. Introduction
During summer frequent episodes of high SO42� and
trace elements concentrations have been observed across
northeastern United States (Husain et al., 1984; Rahn
and Lowenthal, 1984, 1985; Tuncel et al., 1985). Air
trajectories showed that the episodes were invariably
associated with the air masses that had traveled through
the industrial mid-western states before reaching New
York and other northeastern States. The Midwestern
states are very heavy users of coal and emit some 39% of
the country’s total SO2. In addition, large quantities of
trace elements and other chemicals are emitted from coal
burning and other industries. Since then air trajectories
have been extensively used to qualitatively and quanti-
tatively relate the atmospheric SO42� concentrations with
SO2 emissions in the Midwest (Galvin et al., 1978;
Husain et al., 1984, 1998; Husain and Dutkiewicz, 1990).
Unlike SO42�, which can be directly attributed to SO2
emissions, trace elements and other chemical species are
only broadly related to regional emissions because of
multiple undefined sources. However, a similar ap-
proach can also be applied to the measured daily
concentrations of HCl, HNO3, HONO, NH3, and PM2.5
mass (TEOM) at Bronx and Manhattan in New York
City presented in the preceding paper (Bari et al., 2003).
We know of no other work in the northeastern United
States where long-term data has been acquired for
HONO, HNO3, HCl, NH3, and PM2.5 and an attempt
made to link the observed concentrations to regional
emissions. We think this is important to ultimately
elucidate the sources, fates and deposition of these
ARTICLE IN PRESS
AE International – North America
*Corresponding author. Wadsworth Center, New York State
Department of Health Empire State, Plaza Albany, NY 12201-
0509, USA. Tel.: +1-518-473-4854; fax: +1-518-473-2895.
E-mail address: [email protected]
(L. Husain).
1352-2310/03/$ - see front matter r 2003 Elsevier Science Ltd. All rights reserved.
doi:10.1016/S1352-2310(03)00200-0
species. Therefore, in this paper we have applied the air
trajectory analysis to: (1) qualitatively relate the
observed concentrations with regional emissions during
pollution episodes; and (2) use long term concentration
data and air trajectories to quantitatively apportion the
regional contributions of various chemical species.
2. Results and discussion
Bari et al. (2003) have presented the daily concentra-
tions of seven species studied at Manhattan and Bronx
in the preceding paper. The concentrations for all species
are highly correlated between the two sites. Hence only
Manhattan data are presented. In Fig. 1 we have plotted
the frequency distribution of SO42� concentrations at
Manhattan from January 1999 to November 2000.
Concentrations were measured daily on 631 days. The
mean value of the frequency distribution of SO42�
concentrations was 1.0 ppb. The peak in the distribution
was observed at 0.25–0.5 ppb (1–2 mg/m3). The concen-trations decreased sharply to B1 ppb and then taperedoff very slowly. The SO4
2� concentration exceeded
1.25 ppb on 167 days, 2 ppb on 80 days and 2.5 ppb on
47 days. Although these cases of high concentrations are
relatively few, they may have contributed very signifi-
cantly to the atmospheric burden and deposition of
SO42�. It is therefore important to understand the
sources contributing to these high SO42� concentrations
and those of other species studied. Much of these high
concentrations occur as ‘episodes’ lasting over several
days when concentrations of not only SO42� but many
chemical species are elevated.
The data for such an episode that began on 15 July
and ended on 20 July are plotted in Fig. 2. On 13 July
concentrations of all chemical species were low. Con-
centrations increased slightly on 14 July and much more
rapidly on 15 July. From 16 through 19 July the
concentrations were several fold higher compared to
13–14 July. The concentrations abruptly decreased for
all five species on 20 July. In Fig. 3 we have shown the
6 h HYSLIT4 (HYSPLIT4, 1997) air trajectories (to be
described later) reaching New York City on 13, 16, 18
and 20 July. On 13 July, the air trajectories arrived at the
site from the north, a region with few emissions and
hence the low concentrations. On 14 and 15 July the
trajectories, not shown in Fig. 3, were from the Atlantic
Ocean and progressively moved through the states of
New Hampshire, Massachusetts and Connecticut. These
states have relatively higher emissions than the area
traversed by the air masses on 13 July. Compared to 13
July, the enhanced concentrations on 14 and 15 July are
consistent with this observation. The trajectories reach-
ing New York on 16 through 19 July were from the
industrial Midwestern United States—a region well-
known for very high SO2 emissions. Concentrations of
PM2.5, SO42�, SO2, HCl and HNO3 were approximately,
5, 23.9, 6.3, 4.3, and 5.8 ppb, respectively, higher during
16–19 July compared to 13 July. The data suggests that
PM2.5, HCl, and HNO3 are also transported from the
Midwest along with SO42� and SO2. On the other hand,
the concentrations of HONO and NH3 behaved quite
differently than all other species, Fig. 4. HONO
concentrations peaked on 14 and 19 July and were very
low on all other days. Both HONO and NH3concentrations appeared totally unrelated to the air
trajectories. Apparently, atmospheric transport does not
play an important role in determining the concentrations
of HONO and NH3.This is most likely due to the fact
ARTICLE IN PRESS
0 1 2 3 4 7 85 6sulfate (ppb)
0
20
40
60
80
Num
ber
freq
uenc
y
Fig. 1. Frequency distribution of daily SO42� concentrations
from January 1999 to November 2000 at Manhattan.
0
5
10
15
20
SO
2 (p
pb
)
0
1
2
3
4
5
HC
l, H
NO
3 (p
pb
)
SO2 (ppb) HCl (ppb) HNO3 (ppb)
0
10
20
30
40
50
60
13 14 15 16 17 18 19 20
July, 1999P
M2.
5 (u
g/m
3)
0
1
2
3
4
5
6
7
SO
4 (p
pb
)
PM2.5(ug/m3) SO4 (ppb)
Fig. 2. Concentrations of HCl, HNO3, SO2, SO42�, and PM2.5
at Manhattan during the episode of 15–20 July 1999.
A. Bari et al. / Atmospheric Environment 37 (2003) 2837–28442838
that HONO readily photolyses in sunlight resulting in a
residence time of less than a day. The sources of HONO
include auto exhaust, diesel exhaust, and homogeneous
and heterogeneous formation from oxides of nitrogen in
the atmosphere (Pitts et al., 1984; Sjodin, 1988; Sjodin
and Ferm, 1985; Kirchstetter et al., 1996; Arens et al.,
2001). The use of gas stoves in the houses produces
significant amount of HONO, thus affecting the outdoor
pollution in urban areas (Febo and Perrino, 1991).
In the above example we have qualitatively related the
observed concentrations with the direction of the air
flow. It is possible to quantify the source–receptor
relationship by accounting for the time an air mass
spends in a given region using the procedure described
below.
2.1. Air trajectory analysis
To relate the atmospheric concentrations with the
regional emissions the backward-in-time air trajectories
(simply referred to as air trajectories) were used to
apportion the measured daily concentrations of the
chemical species except HONO and NH3. An air
trajectory is a model output of the path that an air
mass followed prior to arriving at location. We used the
HYSPLIT4 (HYSPLIT4, 1997) to compute four trajec-
tories for each day ending at 0100, 0700, 1300, and
1900 h EST. Meteorological data from the EDAS model
(HYSPLIT4, 1997) were used to compute isobaric
trajectories with the initial height set to 1 km. The
latitude and longitude of the air parcel was extracted
every 3 h up to 72 h. Thus, each trajectory had 24 data
pairs of latitude and longitude. We have found that
these settings for HYSPLIT4 give a good representation
of the air flow in the lower 2 km of the atmosphere
ARTICLE IN PRESS
18
16
20
0100 hr070013001900
July 1999
13
Fig. 3. The air trajectories reaching New York City for 0100, 0700, 1300, and 1900h EST on 13, 16, 18, and 20 July 1999 on a
Mercaptor projection map of northeastern North America.
0
1
2
3
4
5
6
7
8
13 14 15 16 17 18 19 20
July, 1999
NH
3 (p
pb
)
0.0
0.4
0.8
1.2
1.6
2.0
HO
NO
(p
pb
)
NH3 (ppb) HONO (ppb)
Fig. 4. Concentrations of HONO, and NH3 at Manhattan
during the episode of 15–20 July 1999.
A. Bari et al. / Atmospheric Environment 37 (2003) 2837–2844 2839
(presumed to be the mixed layer) (Dutkiewicz et al.,
2000).
On a Conformal projection map of northeastern
North America twelve 30� sectors were over laid over
the sites. The air trajectories for air arriving on 13, 16,
18, and 20 July 1999 are also shown in Fig. 3. For
clarity, each point shown represents the location of the
air parcel at 6-h intervals, although all analysis used the
air mass locations at 3-h data sets. The sectors were
numbered in a clockwise direction, with number 1
spanning due north to 30� NNE. The analysis region
was fixed between 35–50� north latitude and 69–95�
west longitude. This is the region that the algorithm used
to convert latitude and longitude into the maps x; y
coordinates is considered to be most accurate. Trajec-
tories extending beyond this region were terminated. A
computer algorithm was used to compute the fraction of
time that each trajectory spent in each sector. The
location of the trajectory during the first 6 h, however,
was excluded since the sectors are not well defined very
close to the origin and a small amount of curvature in a
trajectory can lead to spurious results. To analyze the
daily measurements, results for the four trajectories
from each day were combined to yield the fraction of
time on the ith day that the air had spent in the jth sector
in the past three days (fij). As hourly PM2.5 and SO2measurements were available, 6-h averages centered on
the ending time of each trajectory were used for these
two species. Eqs. (1) and (2) were used to compute the
sector average concentration of species (Cj) and the
percent of the concentration associated with air masses
from sector j (%Cj) (Husain and Dutkiewicz, 1990).
Cj ¼PN
i¼1 Ci fij
Nj
; ð1Þ
where N is the total number of days in the data set,
and the denominator, Nj ; is the total number of daysduring which trajectories passed through sector j;
Nj ¼PN
i¼1 fij
� �:
%Cj ¼CjNjP12j¼1 CjNj
� 100: ð2Þ
To assure more robust statistical significance, the
minimum averaging time used here was three months
(quarter I–IV are defined as, January–March, April–
June, July–September, and October–December, respec-
tively). The quarterly means were then combined with
equal weight to obtain annual means. The predominant
air flow pattern in the Northeast is from west to east.
Sectors 8–10 combined contribute 50%, 58%, 35%, and
49% of the air masses, respectively, for the four
quarters. Sectors 11, 12, and 1 contribute 35%, 21%,
39%, and 41%, respectively, while sectors 5 and 6
contribute only 6% except during the third quarter when
it increases to 15%. Sectors 2–4 contribute only 4–12%
with the highest contribution in the second quarter and
the lowest in the 4th.
Fig. 5a shows the quarterly Cj for sulfate at
Manhattan for quarter 1 and 3, 1999. The strong
seasonal pattern observed earlier (Bari et al., 2003) is
evident in sectors 6–10, but the seasonal variability is not
clearly defined in the remaining sectors, as concentra-
tions remain around 0.5 ppb. C9 for the first and third
quarter was 0.88 and 3.0 ppb in Manhattan. The
quarterly Cj for sulfate for quarter 2 were in between
first and third quarters, the C9 for the second quarter
was 1.65 ppb. During the second quarter the highest Cj
was for sector 8, with a value of 1.9 ppb. The quarterly
Cj for sulfate at Bronx were similar to that at
Manhattan, but with slightly lower values. C9 and C8for third quarter at Bronx were 2.2 and 1.8 ppb.
Elevated sulfate is also associated with air from sectors
9 and 10; however, this is most strongly evident for
Manhattan in the third quarter. The results for 2000 are
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0
5
10
15
20
25
30
35
Sectors
PM
2.5
(ug
/m3 )
Quarter 1 Quarter 3
0.0
0.5
1.0
1.5
2.0
2.5
3.0
1 2 3 4 5 6 7 8 9 10 11 12
1 2 3 4 5 6 7 8 9 10 11 12
1 2 3 4 5 6 7 8 9 10 11 12
SO
4 (p
pb
)
Quarter 1 Quarter 3
0
5
10
15
20
25
30
SO
2 (p
pb
)
Quarter 1 Quarter 3
Fig. 5. Quarterly Cj for SO42�, SO2 and PM2.5 at Manhattan
during first and third quarter 1999. SO2 values measured using
a pulsed fluorescence analyzer model TECO 43S were obtained
from the New York State Department of Environmental
Conservation.
A. Bari et al. / Atmospheric Environment 37 (2003) 2837–28442840
very similar to those shown for 1999. Sectors 8–10
represent air from the west and southwest; including the
states of northern NJ, PA, MD, VA, WV, TN, OH, IL,
IN, KY, MI, WI, and the western most tip of NY. The
southern most tip of Ontario also falls within sector 10.
Since sulfate is a secondary product of sulfur dioxide
oxidation, the strong dependence of sulfate on direction
suggests that distant sources are significant contributors.
We will attempt to quantify this component shortly.
The quarterly Cj for sulfur dioxide at Manhattan for
quarter 1 and 3, 1999 are shown in Fig. 5b. Unlike
sulfate, sulfur dioxide concentrations for all sectors have
the same seasonal dependence, highest in the first
quarter followed by the 4th, 2nd and finally the lowest
in the third. In general the first quarter concentrations
are a factor of 3 higher than those in the third quarter.
While sector 9 has the highest concentrations, sulfur
dioxide does not show the strong directional dependence
seen for sulfate (Fig. 5a). This suggests that local, rather
than any specific distant sources, dominate. The results
for 2000 are very similar to as shown for 1999, except for
sectors 1–6 in first quarter. In 1999 in first quarter the
Cj ’s for sectors 1–6 were between 16.1 and 19.9 ppb, but
during 2000 fluctuated between 8.7 and 23.5 ppb.
The quarterly Cj ’s for PM2.5 at Manhattan for quarter
1 and 3, 1999 are shown in Fig. 5c. The profiles are
intermediate between those of sulfur dioxide and sulfate.
During the first and third quarters the highest and
lowest concentrations differed by 8.3 and 24.1mg/m3,respectively. On the other hand, during the second and
fourth quarters the highest and lowest concentrations
differed by 15.0 and 11.6 mg/m3, respectively. Cj ’s for
quarter 2 were in between first and third quarter. Cj ’s for
quarter 4 were similar to first quarter, but slightly lower
than first quarter. For all quarters the highest PM2.5
concentrations were associated with air from sector 8 or
9 (southwest) and the lowest with air from sectors 12 or
1 (north). The Cj ’s for 2000 are similar to as shown for
1999, except for sector 1–10 for quarter 3 which are
lower than in 1999.
The quarterly Cj for HCl, HNO3, and sulfur dioxide
at Manhattan for quarter 3, 1999 are shown in Fig. 6.
Sulfur dioxide data is added to compare the general
trend. HCl and HNO3 have pattern similar to SO2. For
HNO3, the average Cj for sectors 1–4 and 5–7 are 0.70
and 0.53 ppb, respectively. The Cj then increases to 2.5
and 2.1 ppb for sector 9 and 10, respectively, and then
decreases to 1.4 and 1.2 ppb for sectors 11 and 12. In
case of HCl, the average Cj for sectors 1–4 and 5–7 are
0.45 and 0.27 ppb, respectively. The Cj then increases to
1.04 and 0.90 ppb for sector 9 and 10, respectively, and
then decreases to 0.58 and 0.63 ppb for sectors 11 and
12. Sectors 9 and 10 have the highest concentrations for
HNO3 and HCl, and show strong directional depen-
dence as seen for sulfate (Fig. 5a). Elevated HCl, HNO3are also associated with air from sectors 9 and 10; As
mentioned earlier sectors 8–10 represent air from the
west and southwest; including the states of northern NJ,
PA, MD, VA, WV, TN, OH, IL, IN, KY, MI, WI, and
the western most tip of NY. The southern most tip of
Ontario also falls within sector 10. Again the strong
dependence of concentration on direction suggests that
distant sources are significant contributors to HNO3 and
HCl.
The quarterly Cj for HCl, HNO3, and sulfur dioxide
at Manhattan for quarter 1, 2000 are shown in Fig. 7.
For HNO3, the Cj values fluctuate between 0.2 and
0.5 ppb. In case of HCl, the Cj values fluctuate between
0.13 and 0.29 ppb. In general the Cj for HCl and HNO3are very low and remain almost flat.
ARTICLE IN PRESS
0
5
10
15
20
25
0 1 2 3 4 5 6 7 8 9 10 11 12 13
Sectors (Quarter 3, 1999)
SO
2 (p
pb
)
0.0
0.5
1.0
1.5
2.0
2.5
HC
l, H
NO
3 (p
pb
)
SO2HCl x 2HNO3
Fig. 6. Quarterly Cj for HCl, HNO3, and SO2 at Manhattan
during quarter 3, 1999.
0
5
10
15
20
25
0 1 2 3 4 5 6 7 8 9 10 11 12 13
Sectors (Quarter 1, 2000)
SO
2 (p
pb
)
0.0
0.5
1.0
1.5
2.0
2.5
HC
l, H
NO
3 (p
pb
)
SO2 HCl x 2 HNO3
Fig. 7. Quarterly Cj for HCl, HNO3, and SO2 at Manhattan
during quarter 1, 2000.
A. Bari et al. / Atmospheric Environment 37 (2003) 2837–2844 2841
2.2. Local versus distant sources
We assume that the concentration of SO42�, SO2 or
PM2.5 observed at New York is the sum of contributions
from distant sources and those in the ‘‘metropolitan’’
area. The former is expected to show strong directional
dependence whereas the latter would be largely direc-
tionally independent. From the existing data it is well
known that the sources of non-metropolitan pollutants
lie to the west. The trajectories from southwest to the
northwest are associated with the high concentrations
across New York State (Husain and Dutkiewicz, 1990).
Therefore, we have deduced the background concentra-
tions, Cbkg; based on the trajectories reaching the sitefrom sectors 12 through 4. There are relatively few
sources in these sectors, except small contribution from
marine sources. On the days when trajectories are
exclusively residing in these sectors, the transported
component should be minimal. The mean concentration
from these sectors is defined as ‘‘local background’’.
Realistically, local extends out at least the equivalent of
6 h of air mass transport, as this could not be resolved in
our analysis. Since air mass speeds based on the air
trajectories are 24–30 km/h, local, as used here, is at least
on the order of a 150 km radius around the site. While
this may seem large, the gas phase oxidation of SO2 to
SO42� is at most a few %/h. The largest SO2 emissions
sources are concentrated around the Ohio River Valley,
which is about 1000 km upwind, so this analysis should
have no problem resolving these distant sources from
those nearby.
For sulfate, in 1999, the background concentrations
for the four quarters are, respectively, 0.53, 0.54, 0.60,
and 0.34 ppb, for a mean of 0.50 ppb (the corresponding
mean for the Bronx is 0.42 ppb). Transported sulfate is
only a few tenths of a ppb for the first and fourth
quarters; however, it is 2.3 ppb for sector 9 during the
third quarter and 1.2 ppb for sector 8 during the second.
Combining the transported concentrations and the
percent frequency of air mass from various sectors the
contribution from distant sources can be computed.
Only contributions from sector 6–11 are non-zero. Fig. 8
shows the contribution of transported component after
subtracting background (Cbkg) for sulfate, SO2 and
PM2.5 for first and third quarter. The largest transported
contribution of the sulfate during the third quarter is
from sectors 9 and 10 (sectors due west) contributing
24% and 20%, respectively. During the first quarter
sectors 9 and 10 contribute only 8% and 7.6% of the
sulfate, respectively. During the second quarter the
largest transported contributions are associated with
sectors 8 and 9, giving 16% and 12%, respectively. The
transported component by quarter is, respectively, 31%,
40%, 61%, and 51% for sectors 6 through 11,
respectively. Similar results were obtained during 2000,
and for the Bronx (Table 1).
For sulfur dioxide, concentrations varied less with
direction, so the transported component is expected to
be less significant. For Manhattan based on the 1999
data, the quarterly background concentrations were,
respectively, 13.7, 9.4, 5.5, and 10.5 ppb. The combined
transported component from sectors 6–11 by quarter
was, respectively, 12%, 6%, 17%, and 23%, yielding an
annual mean contribution of only 15%. Similarly, data
from the Bronx site also yielded a 15% annual mean
contribution. Results obtained in 2000 yielded a slightly
higher transported component in Manhattan, 17%, and
a slightly lower one in the Bronx, 11% (Table 1).
Considering the uncertainties in determining the regio-
nal background for sulfur dioxide, these differences are
not deemed significant.
For PM2.5 at Manhattan based on the 1999 data, the
backgrounds for the four quarters were only modestly
different, 11.7, 13.1, 11.5 and 8.9 mg/m3 respectively.Similar backgrounds were obtained for the Bronx. Only
sectors 6–10 had significant transported components.
These components represent only 15% of the mass
during the first quarter, but the transported mass during
ARTICLE IN PRESS
-5
0
5
10
15
20
25
% S
O4
tran
spo
rted
Quarter 1 Quarter 3
-4
-2
0
2
4
6
8
10
% S
O2
tran
spo
rted
Quarter 1 Quarter 3
-5
0
5
10
15
20
1 2 3 4 5 6 7 8 9 10 11 12
1 2 3 4 5 6 7 8 9 10 11 12
1 2 3 4 5 6 7 8 9 10 11 12
Sectors
% P
M2.
5 tr
ansp
ort
edQuarter 1 Quarter 3
Fig. 8. Quarterly transported component (%) after subtracting
background for SO42�, SO2 and PM2.5 at Manhattan during first
and third quarter 1999.
A. Bari et al. / Atmospheric Environment 37 (2003) 2837–28442842
the second through fourth quarters were much more
significant: 24%, 43%, and 38%, respectively. The mass
of sulfate represented on average 17% of the PM2.5
background in 1999 and 20% in 2000. However, the
transported air in sectors 6–10 was far more enriched in
sulfate, averaging around 33% of the PM2.5 mass.
From the observed HNO3 and HCl concentrations
background was subtracted. The net concentrations
were then apportioned to the 12 sectors. The largest
transported contribution of the HNO3 during the third
quarter is from sectors 9 and 10 (sectors due west)
contributing 27% and 32%, respectively. The largest
transported contribution of the HCl during the third
quarter is from sectors 9 and 10 contributing 26% and
31%, respectively. During third quarter about 60% of
HNO3 was local and 40% was transported, and about
74% of HCl was local (including contribution from
marine environment) and 26% was transported. ‘‘Lo-
cal’’ sources, as expected, contributed the most for each
of the two species. On an annual basis 27% of HCl and
24% of HNO3 was transported.
Table 1 summarizes the components of transported
sulfate, sulfur dioxide and PM2.5 based on the air
trajectory analysis. Local and distant sources contrib-
uted roughly equally to the observed sulfate at the two
New York City sites during the third quarter of both
years. However, the transported component for sulfate
averaged only 26% during the first quarter. On an
annual basis, 57% of sulfate was local and 43% was
transported. ‘‘Local’’ sources, as expected, contributed
the lion’s share, 86%, of the sulfur dioxide during the
study period at both sites. The results for PM2.5 fell in
between sulfate and sulfur dioxide. Only 19% and 28%
of the mass was transported during the first and second
quarters, respectively. On the other hand, around 40%
of the PM2.5 came from upwind westerly sources during
the third and fourth quarters, roughly a third of this
mass was sulfate. On an annual basis, 30% of the PM2.5
originated from the distant sources.
3. Summary
Comparison of the air trajectories with the measured
concentrations of SO42�, SO2, HCl, HNO3, NH3, PM2.5
and HONO suggest that a fraction of SO42�, SO2, HCl,
HNO3, and PM2.5 are transported from west and
southwest of New York. HONO and NH3 concentra-
tions appear unrelated to the air trajectories. Air
trajectories were used to evaluate contributions from
the regional emission sources to the observed levels of
sulfur dioxide, particulate sulfate and PM2.5, HNO3 and
HCl. On an annual basis, nearly 40% of sulfate was
transported from the Midwest and B60% from nearby
(B150 km) sources. On the other hand, only B14% of
sulfur dioxide, 30% of the PM2.5, 27% HCl and 24%
HNO3 were transported, with the remaining from
the nearby emissions. During third quarter 1999, about
26% and 40% of HCl and HNO3, respectively, were
transported from the distant sources.
Acknowledgements
The authors thank Stan House, Dan Lince, Dan
Sharron and Pat Palmer for sampling. We also thank the
staff of the New York State Department of Environ-
mental Conservation, Division of Air Resources for
providing NO2, O3 and SO2 hourly data. The financial
assistance provided by the Agency for Toxic Substances
and Disease Registry, and New York State Energy
Research and Development Authority is gratefully
acknowledged.
References
Arens, F., Gutzwiller, L., Baltensperger, U., Gaggeler, H.W.,
Ammann, M., 2001. Heterogenous reaction of NO2 on
diesel soot particles. Environmental Science and Technology
35, 2191–2199.
ARTICLE IN PRESS
Table 1
Apportionment of Transported Species (%)a
Quarter Bronx Manhattan Total Mean
1999 2000 mean 1999 2000 mean
Sulfate
I 33 19 26 31 21 26 26
II 40 50 45 40 49 45 45
III 61 45 53 61 43 52 53
IV 52 45 49 51 42 47 48
Annual mean 47 40 43 46 39 42 43
PM 2.5
I 20 19 20 15 20 18 19
II 24 32 28 24 30 27 28
IIIb 43 28 36 43 27 35 35
IV 43 — 43 38 — 38 41
Annual mean 32 26 29 30 30 30 30
Sulfur dioxide
I 23 17 20 12 24 18 19
II 8 8 8 6 14 10 9
III 14 6 10 17 10 14 12
IV 16 13 15 23 19 21 18
Annual mean 15 11 13 14 17 15 14
aApportionment of concentrations in sectors 6–11 after
background (mean of concentrations in sectors 1–4 and 12)
was subtracted.b In Bronx measurements were only for 1–14 July 1999,
analysis for 2000 includes data through 31 July.
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