Atmospheric Environment 38 (2004) 3179–3189

ARTICLE IN PRESS

*Correspond

Department of

0509, USA. Te

E-mail addr

(L. Husain).

1352-2310/$ - se

doi:10.1016/j.at

Sources of fine particulate sulfate in New York

Vincent A. Dutkiewicza,b, Sumizah Qureshib, Adil R. Khana, Vincent Ferraroa,James Schwabc, Kenneth Demerjianc, Liaquat Husaina,b,*

aWadsworth Center, New York State Department of Health, Empire State Plaza, Albany, NY 12201-0509, USAbDepartment of Environmental Health and Toxicology, State University of New York at Albany, Albany, NY 12201-0509, USA

cAtmospheric Sciences Research Center, State University of New York, Albany, NY, USA

Abstract

Daily PM2.5 sulfate measurements are reported for July 2001 through June 2002 from three New York State sites that

were a part of the New York Supersite Program. The sampling sites were located at Queens, Pinnacle State Park,

and Whiteface Mountain. Quarterly mean sulfate concentrations at these sites were respectively; 5.05, 5.08, and 3.14 mg/m3 during July–September (QIII); 2.84, 2.26, and 1.40mg/m3 during October–December (QIV); 2.71, 2.39, and 1.55mg/m3 during January–March (QI); and 4.17, 4.52, and 2.15 mg/m3 during April–June (QII). Although the sites areseparated by several hundred kilometers and surrounded by highly varied population densities, their sulfate

concentrations have very similar patterns. These data show that sulfate concentrations over broad regions of the

Northeast are correlated. Backward air trajectories were used to evaluate the regional sources of sulfate impacting these

sites. The highest sulfate concentrations at all three sites were associated with air masses that pass through the Ohio

River Valley and the area around the Great Lakes Basin. Moderately high concentrations at Pinnacle and Queens were

also associated with air flow through the Mid-Atlantic states. In addition, we used air trajectories to estimate local

versus transported components. On an annual basis, 44–55% of the sulfate at Queens and 60% at Whiteface and

Pinnacle was transported.

r 2004 Elsevier Ltd. All rights reserved.

Keywords: Sulfate; Particulate matter; Aerosols; PM2.5; Source–receptor relationship

1. Introduction

There is a rising concern over the health impact of fine

particulate matter suspended in the air (e.g., Dockery

et al., 1993; Dockery and Pope, 1994; Gwynn et al.,

2000). Scientific and regulatory interest has focused on

particles smaller than 2.5 mm in diameter (PM2.5). In

addition to the direct health impacts mentioned above,

PM2.5 also impacts aerosol deposition patterns, visibi-

lity, and radiative transfer.

ing author. Wadsworth Center, New York State

Health, Empire State Plaza, Albany, NY 12201-

l.: +1-518-473-4854; fax: +1-518-473-2895.

ess: liaquat.husain@wadsworth.org

e front matter r 2004 Elsevier Ltd. All rights reserve

mosenv.2004.03.029

Most epidemiological studies of suspended particulate

matter (PM) have simply related aerosol mass or PM2.5

mass to some measure of human morbidity or mortality.

However, since PM is composed of varied materials with

diverse physicochemical characteristics, there is a need

to understand the composition of PM2.5 and its

precursors in varied population centers better and

establish source-receptor relations that can help guide

future regulatory decisions.

The PM2.5 Technology Assessment Characterization

Study New York (PMTACS-NY) is a part of the

USEPA Supersite Study program. The goals and

operational procedures may be found on the Web site

(http://www.asrc.cestm.albany.edu/pmtacsny/). The en-

hanced phase of the study was initiated with a month-

long intensive sampling program conducted on and

around the campus of Queens College, Queens, NY in

d.

ARTICLE IN PRESSV.A. Dutkiewicz et al. / Atmospheric Environment 38 (2004) 3179–31893180

July of 2001. Daily PM2.5 aerosols were collected at two

sites. At one of the sites there were co-located samplers

collecting 24 and 6h samples. In addition several

research-grade and commercial gas and aerosol instru-

ments were deployed which included several aerosol

instruments capable of collecting real-time sulfate and/or

nitrate concentrations (Drewnick et al., 2003, 20004a, b).

Results from this program are being published sepa-

rately. Daily sampling sites were established near the

Queens College campus and at two upwind rural sites in

the state. In this paper we present daily PM2.5 sulfate

measurements from these three sites spanning 1 year

(July 2001–June 2002). Using data from the two

up-wind rural sites and air trajectories we evaluate

the sources of the sulfate impacting the Metropolitan

New York area.

2. Methods

2.1. Sampling

The urban site was located in Queens, NY on the roof

of Public School 219 (Queens, or Q). The sampler was

10m above the ground which is 25m above mean sea

level. The site (latitude 40.736�N, longitude 73.823�E)

is adjacent to the campus of Queens College in a

neighborhood that is mainly residential/commercial.

There is a clear view of the Manhattan skyline from

the site. Based on 2000 census data, the population

density of Queens County is 52,800 people/km2. In

addition to normal urban street traffic there is a very

busy 6- to 8-lane interstate, I 495, that runs east and west

1.2 km north of the site and there are four additional 4-

to 6- lane highways within a radius of 5 km. The daily

PM2.5 samples (midnight–midnight, EST) were collected

from July 2001 through June 30, 2002 using a Rupprecht

& Patashnick ACCU sampler. The ACCU sampler is an

accessory on the Model 1400a particle mass analyzer.

After size separation, the air flow stream is split and

13.67 l/min (lpm) is sequentially drawn through 47-mm

2-mm pore size Zefluor filters. Air flow was controlled

with electronic mass-flow controllers to minimize the

errors in sampling volume, estimated at 72%. All airvolumes have been corrected to a temperature of 25�C

and a pressure of 1 atm. In addition to the Queens site

daily PM2.5 samples were also collected with ACCU

samplers at Pinnacle State Park in Steuben County

(Pinnacle, or P), and at Whiteface Mountain Lodge in

Essex County (Whiteface, or W). Pinnacle (42.091�N

and 77.210�E) is west and slightly north of New York

City at an elevation of 507m (see Fig. 5 for map with site

locations). The sampler was 5m above the ground. The

line of sight angle is 297� and the distance is 350 km.

Whiteface (44.393�N and 73.859�E) is almost due north

of New York City in the Adirondack Mountain region

of the state (Lodge elevation 600m) at a distance of

390 km. The sampler was located at ground level.

Whiteface is 390 km northeast of Pinnacle. The popula-

tion densities in Steuben and Essex Counties are 183.6,

and 55.9 people/km2, respectively, tiny compared

to the density in Queens. Because of the prevailing

westerly winds, all three sites are influenced by sulfate

transport from high SO2 emission sources in the

Midwest (Husain et al., 1998; Bari et al., 2003a, b).

Since Pinnacle and Whiteface have few nearby SO2emission sources, the data from these sites can be

expected to more accurately gauge transported sulfate

and help separate ‘‘local’’ versus transported compo-

nents at Queens.

2.2. Analysis

The aerosol samples were stored in sealed plastic Petri

dishes until analyzed. The entire filter was placed in 7ml

of distilled water and ultra-sonicated at 70�C for 90min.

One milliliter was removed for analysis of major anions

by ion chromatography (IC). The remaining solution

was stabilized against trace metal loss by addition of

nitric acid to a final concentration of 0.15%. A 1ml

aliquot was removed to determine soluble trace

metals by inductively coupled plasma mass-spec

analysis. The filter and the remaining 5ml were

digested in a microwave oven using hydrogen

peroxide, nitric acid, and hydrofluoric acid and

analyzed by inductively coupled plasma mass-spec

analysis for trace elements. We present the sulfate

results in this paper. The trace metal data will be

reported elsewhere.

After extraction, samples were kept refrigerated

until analyzed. The IC analysis was conducted

using a Dionex Model 500 composed of a high-pressure

pump, guard column, analytical column, anion

self-regenerating suppressor conductivity detector

(CD20), and auto-sampler and was equipped

with Peaknet software (Khwaja et al., 1999).

To maintain a high degree of linearity and thus limit

bias, the peak for sulfate was calibrated over the

range of 0.02–20mg/l, and any sample with

concentration above this range was diluted and

re-analyzed (usually 2–4� dilution). The analytical

column used was an Ion Pac AS4A (4� 250mm) andguard column AG4A (4� 50mm) with a 25-ml loop.A carbonate and bicarbonate eluent was used that

consisted of a mixture of 1.8mMNa2CO3 and

1.7mMNaHCO3, with a 1.6ml/min flow. The sulfate

retention time is 6.0min and the minimum reportable

level (MRL)was 0.10mg/l or 0.04mg/m3. At Pinnacleand Queens, all sulfate measurements were above the

MRL compared to 98% of the measurements at

Whiteface. Further details of the IC method may be

found in Khwaja et al. (1999).

ARTICLE IN PRESSV.A. Dutkiewicz et al. / Atmospheric Environment 38 (2004) 3179–3189 3181

3. Results

3.1. Trends and statistics for sulfate, July 1, 2001–June

30, 2002

Daily PM2.5 sulfate concentration at the three sites are

shown in Fig. 1. The data show the highly regional

character of sulfate. Even though the sites are separated

by 350–390 km and represent highly varied local

environments, there are distinct similarities in the peaks

and valleys of sulfate concentrations. In fact, over the

entire year daily sulfate at Whiteface and Pinnacle are

highly correlated ðr ¼ 0:73Þ: This is followed by

Queens and Pinnacle ðr ¼ 0:56Þ and Queens and

Whiteface ðr ¼ 0:43Þ: This implies a significant regionalsulfate component. All the correlation coefficients are

significant at p ¼ 0:001 but especially those for

Pinnacle versus the other sites. Pinnacle is the

westerly most site and air mass movement is

predominantly from west to east. There are large

SO2 emission sources west of Pinnacle in the Ohio

River Valley/Midwest which have been shown to have a

major impact on the sulfate concentration at Mayville

and Whiteface Mt., NY (Parekh and Husain, 1982;

Husain et al., 1984; Husain and Dutkiewicz, 1990;

Husain et al., 1998; Dutkiewicz et al., 2000). (Mayville is

located due west of Pinnacle very near to Lake Erie, see

Fig. 5.) Qualitatively, Fig. 1 and the high degree of

correlation between sulfate at Pinnacle and Queens

suggests those Midwest SO2 sources also have a major

impact at Queens. We will quantify this impact later in

this paper.

07/01 07/31 08/30 09/29 10/29 11/28 12/

2001

0

10

20

30

40

Sul

fate

(µg

/m3 )

Whiteface Lodge + 30 µg

Pinnacle State Park +

Que

Fig. 1. Time series of daily PM2.5 sulfate concentrations measured at

between July 1, 2001 and June 30, 2002.

The seasonal pattern of sulfate at the three sites are

markedly similar. The largest variability and highest

concentrations of sulfate in Fig. 1 occurred from April

through September, the ‘‘warm months’’. While during

October–March, the ‘‘cold months’’, sulfate is system-

atically low and less variable. October and April are the

transition months (Dutkiewicz et al., 2000). A summary

of the monthly mean sulfate concentrations and the

number of samples collected at the three sites are given

in Table 1. The highest monthly means at all sites were

recorded in August. Note that the August sulfate

concentration at Queens and Pinnacle differ by only

0.4 mg/m3 even though one site is in an urban center andthe other is relatively remote. In fact, monthly means at

Pinnacle and Queens differ by more than 0.5 ug/m3 in

only 4 of the 12 months. Sulfate concentrations at

Whiteface are systematically lower than that of the other

sites. Monthly means during the cold months are around

1 mg/m3 at Whiteface and 2mg/m3 at Pinnacle andQueens. We will primarily discuss the data on a

quarterly basis as defined in Table 1, however, to

maintain more robust statistical weight for the air

trajectory analysis the data will be combined semi-

annually using the warm and cold month designations

discussed earlier.

The quarterly statistics at the three sites are summar-

ized in the box plot shown in Fig. 2. During QIII (2001)

the maximum concentrations at the three sites varied

from 20 to 25mg/m3. The median at Queens and

Pinnacle, 3.5 and 3.8mg/m3, respectively, and the

minimum concentrations, 0.3 and 0.2 mg/m3, respec-tively, are all very similar. Concentrations at Whiteface

28 01/27 02/26 03/28 04/27 05/27 06/26

2002

/m3

15 µg/m3

ens (PS 219)

Whiteface Lodge, Pinnacle State Park and Queens, New York

ARTICLE IN PRESS

Table 1

Summary of monthly sulfate measurements at three sites in New York State

Month Pinnacle State Park Whiteface Mt. Lodge Queens (P219)

Days sampled Mean (mg/m3) N Mean (mg/m3) N Mean (mg/m3)

2001

July 25 4:8 31 2:6 30 4:3August 29 7:4 30 4:1 31 7:8September 30 3:0 30 2:7 30 3:1Q III means 5:1 3:1 5:1

October 29 1:9 30 1:5 31 2:9November 30 2:9 29 1:7 30 2:9December 31 1:9 31 1:0 31 2:7Q IV means 2:3 1:4 2:8

2002

January 30 2:3 30 1:6 31 2:5February 20 1:8 28 1:0 28 2:2March 28 3:0 28 2:0 31 3:5Q I means 2:4 1:6 2:7

April 27 3:0 30 1:5 28 3:2May 30 3:3 31 2:0 22 2:7June 25 7:3 28 2:9 18 6:3Q II means 4:5 2:2 4:2

Fig. 2. Box plots showing the quarterly statistics of daily

sulfate measurements from Fig. 1. The solid dots are outliers

generated by the graphics software. The quarters run chron-

ologically from left to right with Quarter III, 2001 on the

far left.

V.A. Dutkiewicz et al. / Atmospheric Environment 38 (2004) 3179–31893182

cover a larger range since maximum concentrations are

similar to Queens and Pinnacle, however, values at the

detection limit, 0.04 mg/m3, are also encountered. Themedian sulfate at Whiteface, 1.3 mg/m3, is correspond-ingly much lower than the other two sites. During QIV

the maximum sulfate concentration at the three sites

decreased to 6.8–8.3 mg/m3. During QI (2002) the

maximum concentration was similar to QIV at Queens

and Pinnacle but only around half as large at Whiteface,

4.6mg/m3. During QII the maximum concentration wassimilar to QIII B20mg/m3. Thus Fig. 2 confirms thesimilarity of sulfate at these highly varied and widely

separated sites. The similarity of the box plots for

quarters QII and QIII and quarters QI and QIV in Fig. 2

also shows that separating the year into warm and cold

halves preserves the seasonal variation of sulfate.

The data collected in this work at Queens may be

compared to a 2 year study conducted at Manhattan

and Bronx (Bari et al., 2003a, b) as the threes sites fall

within a circle of only 8 km radius. Daily PM2.5 sulfate

was measured on the roof of Mabel Dean High School

in Manhattan (23m above ground level) and Inter-

mediate Schools 155 and 52 in the Bronx (13m above

ground level) from January 1999 to November 2000.

Both of these roof-top sites were at comparable levels

to near-by buildings. In the Manhattan/Bronx study

sulfate was measured on PM2.5 aerosol samples that

were preceded by Annular Denuders coated to remove

acidic gasses and ammonia, however, neither are known

to impact aerosol sulfate measurement. The quarterly

statistics from these sites are compared to those from

Queens in Table 2. In spite of the fact that the

measurements were 2 years apart and from different

parts of the NY metropolitan area which have different

street level character, the sulfate concentrations were

quite similar. For example, median sulfate concentration

differs by as little as 0.1–0.2 mg/m3 in QI and QIV andthe largest difference was 0.4mg/m3 during QIII forManhattan and the Bronx. In this case the median

sulfate concentration for Queens falls in between them.

Thus, the sulfate concentrations for Queens are quite

representative of the metropolitan New York area. In

the next section we quantify sulfate concentration as a

function of direction and source regions.

ARTICLE IN PRESS

Table 2

Summary statistics for PM2.5 sulfate at selected sites in metropolitan NYa

Maximum 75% Median 25% Minimum Mean

Quarter I

Manh., 1999, 2000 9.5 4.1 2.9 1.9 0.6 3.2

Bronx, 99,00 7.8 3.7 2.7 1.7 1.8 3.0

Queens, 02 9.7 3.2 2.4 1.8 0.6 2.7

Quarter II

Manh., 99, 00 15.4 5.0 3.0 1.9 0.5 4.0

Bronx, 99,00 15.8 4.7 2.9 1.7 0.5 3.9

Queens, 02 14.2 4.4 2.9 2.0 0.8 3.9

Quarter III

Manh., 99, 00 24.1 7.5 3.7 1.9 0.3 5.5

Bronx, 00 13.9 6.3 3.3 1.8 0.4 4.7

Queens, 01 18.8 7.7 3.5 1.8 0.3 5.1

Quarter IV

Manh., 99, 9.7 3.8 2.2 1.6 0.6 2.9

Bronx, 00 8.7 3.6 2.2 1.4 0.2 2.7

Queens, 01 8.3 3.8 2.4 1.4 0.3 2.8

aQueens (this work), Manhattan and the Bronx (Bari et al., 2003a, b).

Fig. 3. Sulfate concentrations versus the 12 sector directions as

explained in the text; (A) Cj for Queens averaged over the warm

(April–September) and cold (October–March) periods and (B)

comparison of annual Cj at Queens (this work) with similar

results for Manhattan and the Bronx from Bari et al. (2003b).

Vertical bars show estimated uncertainties based on the

statistical weighting of the air masses for each sector.

V.A. Dutkiewicz et al. / Atmospheric Environment 38 (2004) 3179–3189 3183

4. Discussion

4.1. Sulfate concentrations versus air mass direction

To elucidate the relationship between sulfate concen-

tration at the three sites and to delineate the SO2 source

regions contributing to the observed sulfate, air trajec-

tories were computed for each site. Four backward in time

air trajectories (72h) were computed for each day (0100,

0700, 1300 and 1900h, EST) using the HYSPLIT 4 model

with EDAS meteorologic input (HYSPLIT4, 1997). The

run options were selected to delineate long distance

transport as discussed in Dutkiewicz et al. (2000).

To evaluate the influence of air mass direction on

observed sulfate concentrations we use 12 30� sectors

designated like in a clock. For each trajectory we

determine the time spent in each sector (tj) based on the

number of 3 h trajectory locations that fall in each

sector. To evaluate daily measurements the tj from the

four trajectories are combined for each day (i) yielding

tij :Methods to compute sector mean concentrations (Cj)

and the relative contribution of a species to a given

sector (%Cj) may be found elsewhere (Parekh and

Husain, 1982; Husain and Dutkiewicz, 1990).

Sulfate concentrations associated with air trajectories

from different directions were evaluated on a semi-

annual basis for the cold and warm periods to

obtain sufficiently long averaging periods to minimize

the impact from precipitation and singular events.

The sulfate Cj for Queens are shown in Fig. 3A. The

uncertainty of Cj shown in Fig. 3 is based on the

ARTICLE IN PRESS

Fig. 4. (A) Radial plot of sulfate as a function of the 12 sector

directions ðCjÞ superimposed on to of a map of the Northeast.The largest ring at each site is 8mg/m3 and there is 2 mg/m3

between each ring. (B) Same as A except sulfate are normalized

to the frequency of the air masses and expressed as a percent.

The largest ring at each site is 40% and there is 10% between

each ring.

V.A. Dutkiewicz et al. / Atmospheric Environment 38 (2004) 3179–31893184

uncertainty in daily sulfate concentrations, air trajec-

tories and the statistical weight of the air masses from a

given direction. During warm periods C7–10 are sig-

nificantly higher than for sectors 1 through 6, 11 and 12.

The consistently low concentration in the latter eight

sectors can be taken as the ‘‘baseline’’ in the profile with a

distinct peak in concentrations for sector 9. At 7.0mg/m3,C9 is 2.8 times the mean for C1–6. On the other hand,

C11,12 are only 20% higher than the C1–6 mean. Sectors

12 and 1 combined represent air from the north, sectors

3 and 4 represent air from the east, 6 and 7 correspond

to air from the south, and sectors 9 and 10 represent

westerly air flow. Thus the highest Cj in Fig. 3A

represent westerly air flow or air that has passed through

the high SO2 emission region in the Industrial Midwest.

Things are somewhat different during the cold period.

The lowest Cj occurs for sectors 1–3, 1.5mg/m3, followed

by sectors 11and 12, 1.8 mg/m3, and then 4–6, 3.0mg/m3.Unlike the warm period, Cj for sectors 4–6 is twice that

for sectors 1–3. Air from sectors 4–6 must pass over

Queens and Long Island while air from sectors 1–3

approximately passes over the New England States. The

air from sectors 1–6 has a very low frequency of

occurrence, 2.3% of the time for sectors 1–3 and only

2.7% of the time for sectors 4–6. This is reflected in the

high relative uncertainty in Fig. 3A. The highest Cj is

still for sector 9, however, concentrations are now only

3.6mg/m3 and the Cj for sectors 7, 8, and 10 are similar.

Fig. 3B compares the Cj profile averaged over a full

year in Queens to that obtained for Manhattan and the

Bronx during the 1999–2000 Asthma study (Bari et al.,

2003b). The air trajectories used for the Asthma study

were computed in the same manner as those used in this

work. For Manhattan and the Bronx the profile

represents nearly 2 year of daily data. The profiles for

Manhattan and the Bronx differ by 10% or less for

sectors 3–9, around 15% for sectors 2, 10, and 11 and

around 20% for sectors 1 and 12. Based on air mass

frequency these differences are not considered to be

significant, so the profiles are essentially the same. Since

the Bronx and Manhattan data are in excellent

agreement, only the Bronx profile is compared to

Queens in the discussion below. The Cj at Queens in

2001–2002 for sectors 10–12, 1–4 and 6, 8 agree within

uncertainties with the Bronx concentrations. Sector 9 for

Queens is lower by 12% while sector 5 is lower by 22%.

The uncertainty for sectors 4 and 5 is estimated at 22%

as the air mass frequency is only 1%. Within uncertain-

ties, year to year differences in meteorological condi-

tions can account for the small differences. For 1999 and

2000 the combined SO2 emissions for the Midwest,

defined here as PA, OH, WV, KY, MI, IN, IL and WI,

was respectively 7040 and 6670 kilometric tons per year

(USEPA, 2002). Emissions for the Midwest in 2001 was

6050 kilometric tons per years or 12% lower than the

mean for 1999 and 2000. Emissions for 2002 are not yet

available but are expected to be comparable to 2001 or

lower. Thus, the lower Cj for sectors 8 and 9 in Queens

may, at least in part, be a direct response to the lower

SO2 emissions upwind.

The directional pattern for sulfate obtained at

Pinnacle and Whiteface are compared to that for Queens

in Fig. 4A. To aide this comparison, the Cj are drawn on

radial plots superimposed on a map of the region. In

Fig. 4A the highest sulfate Cj at all three sites are

focused towards the Ohio River Valley and area around

the Great Lakes Basin. Moderately high concentrations

at Pinnacle and Queens are also associated with air flow

through the Mid-Atlantic States. At Pinnacle there is

also a spike in sulfate for easterly flow. Based on the tj

ARTICLE IN PRESSV.A. Dutkiewicz et al. / Atmospheric Environment 38 (2004) 3179–3189 3185

the uncertainty is around715%.The sulfate for easterlyair flow in the cold period was comparable to that for

northeasterly air flow so this spike may be an anomaly.

We will be able to further evaluate this as more data are

collected in the future.

4.2. Apportionment of sulfate source regions using air

trajectories

The impact of a source region on the sulfate at a

receptor depends on both the concentrations accumu-

lated by the air mass during transport and the frequency

of air masses. The former is represented by Cj evaluated

in Figs. 4A and the latter are the tj computed by the

trajectories. Air most frequently arrives from the west

and northwest and there is very low impact from the

southeast quadrant (sectors 4–6). By taking the product

of Cj and tj and normalizing by the sum of the product

over all sectors yields the percentage of sulfate impacting

from each sector. This is shown for the three sites in

Fig. 4B. At Queens 44% of the sulfate is associated with

westerly air flow, 25% with southwesterly, 19% with

northwesterly, and other directions have negligible

contributions. The results at Pinnacle are similar 42%

from the west, 26% for the southwest, 18% from the

northwest and very small components from the other

directions. The pattern at Whiteface is shifted towards

the southwest, 47% from the west, 37% from the

southwest, 12.9% from the northwest, and a very small

component from the other directions. Another differ-

ence between the sites is a somewhat larger southerly

components at Pinnacle, 6.8% compared to 4.4% at

Queens and Whiteface at 5.5%.

4.3. Evaluation of local versus transported components

at Queens

As discussed above it is clear that the highest sulfate

concentrations are associated with westerly air flow,

however, this does not differentiate the sulfate that is

transported from upwind sources from that produced

locally. At all three of the Metropolitan sites in Fig. 3B,

sectors 1–4 and 11 and 12 had similar concentrations,

mean 2.2mg/m3. Sectors 5 and 6 for Manhattan and theBronx are somewhat higher averaging 3.5 mg/m3 com-pared to 2.3mg/m3 for Queens. Assuming that sulfate atQueens is the simple sum of contributions transported

from distant sources and contributions from the

Metropolitan area, these components can be de-con-

voluted with the help of the air trajectories. The former

should show a strong dependence on direction while the

latter should be largely independent on direction. Based

on these assumptions Bari et al. (2003b) estimated local

and transported components for sulfate, sulfur dioxide

and PM2.5 from the Asthma study data collected in

Manhattan and the Bronx. The similarity of the baseline

concentration at the three Metropolitan sites in Fig. 3B,

supports the assumption that the baseline Cj represents

a homogenous local contribution. The local concentra-

tions were obtained by averaging Cj for sectors 12 and

1–4 (sectors 12–4). Note the lack of significant variation

of Cj over these sectors in Fig. 3A. As discussed by Bari

et al. (2003b) local as defined by this method is at least

the equivalent of 6 h mass transport as this could not be

resolved in our analysis. Since air mass speed based on

trajectories are 24–30 kmh�1, local, is at least of the

order of 160 km radius around the site. Also, this

approach cannot account for contributions from more

distant sources in the direction of sectors 12–4, so the

local sulfate concentration should be taken as an upper

value. On a semiannual basis the local component is

1.75 mg/m3 for the cold period and 2.4 mg/m3 during thewarm. These are almost identical to the values obtained

for 1999 in Manhattan (Bari et al., 2003b).

Evaluating local sulfate at Whiteface and Pinnacle

with this method is a bit more error-prone since there is

a low population and the lack of significant industry

around the sites. Thus, local sources may be small

individual point sources and the assumption of a

homogenous local baseline may not be as appropriate

as in a large metropolitan area. With this caution in

mind we have evaluated the baseline sulfate at Pinnacle

and Whiteface. This was very straight forward at

Whiteface as sectors 12–4 were low and of comparable

values during the warm and cold periods, 0.6 mg/m3.This was also true for Pinnacle during the cold period as

sectors 12–4 averaged only 0.8 mg/m3. This is in spite ofthe fact that there are significant SO2 emission point

sources (between 10,000 and 50,000 tons/year) within

125 km to the north around Rochester, NY and 210 km

to the north northwest around Buffalo, NY. Even

excluding sectors 3 and 4 the baseline for the warm

period is 0.8mg/m3, higher than the cold period, perhapsreflecting contributions from the SO2 emission sources

around Buffalo and Rochester. Unfortunately, air

trajectories from this direction occur infrequently so

the uncertainty for this number is very large. Taking into

account the lack of a seasonal variation at Whiteface, a

background for Pinnacle of 0.8 mg/m3 over both seasonsseems appropriate.

An alternate method to evaluate the local sulfate

component at a complex urban site like Queens is to

compare measurements to an upwind rural site. We

discussed earlier that the daily sulfate concentration at

the three sites are significantly correlated, however,

localized events like precipitation can blur the correla-

tion. Thus, in this case, a longer averaging time may be

helpful. There are total sulfate measurements made on a

weekly basis at various CASTNet sites around the

Northeastern US (Baumgardner et al., 1999). Table 3

lists the nearby CASTNet sites along with our site at

Mayville, NY. Locations are indicated in Fig. 5. The

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Table 3

Summary of selected sites in the Northeast and regression coefficients for weekly sulfate versus that at Pinnacle State Park

Site name Short name (site no.) Program Regression coefficients versus Pinnacle sulfatea

N Slope Intercept r2

Pennsylvania State University, PA PSU (106) CASTNetb 48 1.22 0.03 0.89

Kane Experimental Forrest, PA KEF (112) CASTNet 47 1.16 0.14 0.93

M.K.Goddard, PA MKG (113) CASTNet 47 1.14 0.10 0.85

Mayville, NY M NYSDOHc 43 1.07 �0.26 0.92

Queens, NY Q this work 45 0.87 0.84 0.81

Connecticut Hill, NY CTH (110) CASTNet 42 0.84 0.31 0.95

Washingtons Crossing, NJ WNJ (144) CASTNet 44 0.84 0.64 0.80

Claryville, NY CLV (175) CASTNet 47 0.78 0.46 0.85

Whiteface Mt. Lodge, NY W this work 45 0.67 �0.22 0.85

Lye Brook, VT LYE (145) CASTNet 45 0.60 0.43 0.82

aLinear regression between weekly sulfate concentrations (July 2001–June 2002) and that at Pinnacle. Some outliers were removed.b (Baumgardner et al., 1999) Data downloaded from web site http://www.epa.gov/castnet/data.cNew York State Department of Health (Husain et al., 1998).

Fig. 5. Map of the northeast showing the location of the sites listed in Table 3. Also shown are scatter plots of weekly sulfate at each

site versus concentrations at Pinnacle over the period July 2001 through June 2002. Lines are the result of linear regression fits to the

data. Regression parameters are summarized in Table 3.

V.A. Dutkiewicz et al. / Atmospheric Environment 38 (2004) 3179–31893186

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Fig. 6. Bar plots showing sulfate concentration at Queens as a

function of sectors (solid, same data as Fig. 3A) averaged over

the warm periods (A) and cold periods in (B) and the

transported component (hashed) obtained by subtracting the

baseline concentration shown as the dashed horizontal line.

Vertical bars are uncertainties based on the statistical weighting

of the air masses for each sector.

V.A. Dutkiewicz et al. / Atmospheric Environment 38 (2004) 3179–3189 3187

CASTNet program uses open face 47mm Teflon filters

sampled at 1.5 lpm over 7 days. At Mayville daily total

suspended particulate samples are collected (Husain

et al., 1998). Comparisons between PM10 and PM2.5

sulfate from 14 urban sites in the Canadian sampling

network indicated that 86% of the total sulfate was

measured on PM2.5 samplers (Brook et al., 1997). This

factor has been applied to the CASTNet and Mayville

sulfate concentrations to make them consistent with

PM2.5 sulfate. The daily samples from Pinnacle, White-

face, Queens and Mayville were averaged over the same

weekly time periods as the CASTNet samples. Fig. 5

shows scatter plots for the weekly sulfate at various sites

relative to those at Pinnacle. The results of linear

regression fits (solid lines) are given in Table 3. For a few

of the sites, 2–3 outlier points have been excluded.

Although precipitation should have less impact over a

weekly mean, unique variations may occur and should

be removed. The regional or transported sulfate

component should be reflected in the quality of the

regression fits and the slope the regression line while

local contributions should be reflected in the y-intercept.

All the regression coefficients ðr2Þ are 0.81 or greater andall but 3 of the sites have r2 greater than 0.85. Thus all

the linear fits are significant at p ¼ 0:001:The closest site to Pinnacle is CASTNet site 110 at

Connecticut Hill NY; only 55 km to the northeast. It is

also located in a forested area. Unfortunately, there

were five missing data points from this site during July

and August of 2001 when sulfate concentrations are the

highest. A few missing days at Pinnacle negated three

other data pairs compounding the problem. Thus, there

were only 42 data pairs for this regression and only one

pair had concentrations 6mg/m3. While the regressioncoefficient is quite good at 0.95, the limited range of

comparable sulfate measurements with Pinnacle makes

the results of this regression rather uncertain. Thus, the

intercept of 0.3 mg/m3 may not be significant. Data fromthe summer of 2002 may alleviate this problem.

Slopes for the sites west of Pinnacle and at PSU

(upwind) are greater than 1.0. This indicates they have a

greater regional sulfate component than that at Pinna-

cle. Since these sites are closer to the high SO2 emission

region in the Midwest, this result is not surprising. Note

that the intercepts at all the four sites is near zero

suggesting that their local sulfate must be similar to

Pinnacle.

All of the sites east (downwind) of Pinnacle have

slopes less than 1. This is consistent with a reduced

regional sulfate component which again is not surprising

since these sites are farther from the main source region.

The lowest slopes are for the more northerly sites

(Whiteface and Lye Brook). The slopes for Queens,

CLV and WNJ are all around 0.8 suggesting similar

regional sulfate components. The intercepts, however,

differ from site to site; the lowest at CLV (0.46) and the

highest at Queens 0.84. This suggest a local sulfate

component for Queens of 0.84 mg/m3 relative to that atPinnacle. Adding this to the 0.8mg/m3 deduced forPinnacle, based on air trajectories yields a local sulfate

concentration of 1.6mg/m3. For Whiteface and Pinnaclein Fig. 5 the regression coefficient is somewhat better

than that for Queens and the intercept, �0.22, isessentially zero. This is consistent with the trajectory

analysis which gave similar background levels for these

sites. The nearest site to Queens is no. 144 at

Washington Crossing, NJ. The site is in western NJ in

an area listed as agricultural-urban and it is only 100 km

southwest of Queens. The slope, 0.84, is similar to that

for Queens and the intercept is slightly lower at 0.64mg/m3, however, a significant local component of sulfate is

indicated. As this site is just upwind of Queens, local

sulfate here will also impact the metropolitan area.

Slightly more northwest of Queens at CLV the local

sulfate is only 0.46. The southern Vermont site (LYE)

has a similar intercept, 0.43. This suggests a modest local

sulfate component for this area. The scatter plots

relative to Pinnacle in Fig. 5 show a very systematic

pattern for sulfate pointing to a primary source west of

Pinnacle and a local sulfate background at Queens of

around 1.6mg/m3. This is comparable to the 1.8mg/m3

obtained earlier for the cold season but significantly less

than the 2.4 mg/m3 obtained for the warm season.

ARTICLE IN PRESSV.A. Dutkiewicz et al. / Atmospheric Environment 38 (2004) 3179–31893188

Fig. 6 shows Cj ; the local baseline based on airtrajectories, and the resultant transported sulfate ðTjÞ forQueens. During the cold period Tj ’s are less than the

local baseline value except for sector 9 which is 1.6

mg/m3. Fig. 6B also indicates the potential for small tomoderate transported components for sectors 7, 8 and

10, while the small positive differences for sectors 4–6

are within the uncertainties of Cj for those sectors and

are not considered significant. Integrating the shaded

bars and the baseline sulfate during the cold period

yields 39% of the sulfate as transported. Of this, 88% is

associated with sectors 8, 9, and 10. If 1.6 mg/m3 is usedfor the local sulfate the transported component is

increased to 44%.

For the warm period in Fig. 6 there is a large

transported component for sectors 8–10. The positive

difference for sector 7 is marginally significant. For

sector 9, the transported component represent 4.2 mg/m3

or a factor of 1.8 time the baseline. The Cj ’s for sectors 6

and 11 are essentially equal to the baseline value

suggesting negligible transported components. Integrat-

ing the shaded area in Fig. 6 for the warm period yields

48% transported. Once again, the sectors 8, 9,

and 10 contributed 87% of transported component.

If 1.6mg/m3 is used for the local sulfate, the

transported component is increased to 65%. On an

annual basis, the present data indicates that

between 44% and 55% of the sulfate at Queens is

transported. Bari et al. (2003b) obtained a 46% annual

average for Manhattan and the Bronx in 1999 and 40%

in 2000, in excellent agreement with the present results

from Queens. Transported sulfate at Whiteface and

Pinnacle are much larger, 72% and 62%, respectively,

integrated over the warm months and 49% and 60%

integrated over the cold. Thus, on an annual basis 60%

of the sulfate is transported at Whiteface and at

Pinnacle.

5. Summary and conclusions

Significant observations and conclusions based on the

first year of daily sulfate measurements at the three

New York Supersites are:

* Sulfate concentrations over broad regions in the

Northeast are highly correlated.* Day to day human activities do not appear to

contribute significantly to the PM2.5 sulfate since

sites with grossly different population densities can

have essentially the same concentrations.* Based on air trajectories and on an annual

basis at Queens, 44–55% of the SO42� is trans-

ported from distant sources. This value for

Pinnacle State Park and Whiteface Mountain

is 60%.

Acknowledgements

This work was supported in part by the New York

State Energy Research and Development Authority

(NYSERDA), contract no. 4918ERTERES99, the US

Environmental Protection Agency (EPA) cooperative

agreement no. R828060010 and New York State

Department of Environmental Conservation (NYS

DEC), contract no. C004210. Although the research

described in this article has been funded in part by the

US Environmental Protection Agency, it has not been

subjected to the Agency’s required peer and policy

review and therefore does not necessarily reflect the

views of the Agency and no official endorsement should

be inferred. The assistance of Pamela Kruger in data

reduction is gratefully acknowledged.

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