Successes and Challenges in Managing Urban Air Pollution:
The New York City Experience
Jack Caravanos, DrPH
Hunter College of the City University of New York,
Urban Public Health Program, School of Health Sciences
New York, New York
A. Introduction and Background
The year 2000 marks the 30th anniversary of the Clean Air Act (CAA). This landmark federal
legislation, born from the turbulent times of late 1960’s in US history, set air pollution standards,
established air emissions limits and generated dozens of programs designed to improve air
quality.1-3 Thirty years later, ambient air in the United States is significantly cleaner and in many
urban areas, rarely exceeds the ambient air quality levels set by this law. While several cities in
the United States continue to have unacceptably high air pollution and numerous air pollution
episodes, the criteria air pollutants levels set by the US Environmental Protection Agency are no
longer the challenge. Instead, new initiates and goals are being set to further reduce emissions
and improve air quality. This paper will present the current New York City trends in overall air
quality and pollutant emissions and discuss the reasons for the continuing improvements in urban
air quality.
Air pollution regulation in the US has taken a two-tier approach; setting air quality standards and
regulating air emissions.2 While it may seem obvious that these two are closely related (i.e. the
more contaminant emissions in an area, the lower the overall air quality), in many counties in the
US this is not necessarily the case. Given the significant influences of geography, atmospheric
and climatic conditions on contaminant dispersion, many areas in the US have acceptable air
quality but lead the country in air emissions (notably the Northeast). This interesting
discrepancy will be discussed later on in the paper.
National Ambient Air Quality Standards
Presently the US EPA has set 6 National Ambient Air Quality Standards (NAAQS). Table 1 lists
these air contaminants and their regulatory limits.3 Originally there were 7, however, US EPA
eliminated the NAAQS for hydrocarbons and established separate regulations for this diverse
group of contaminants and renamed it; Hazardous Air Pollutants. The ambient air quality
1
standards were initially selected because of the ubiquitous nature of these contaminants in US
cities and urban areas. Federal regulations mandate specific air sampling programs for
monitoring these contaminants. The number of sampling sites, location and frequency of
sampling is determined through air emissions data and population.4
TABLE 1: US Environmental Protection Agency National Ambient Air Quality Standards
Air Quality Parameter
Inhalable Particulates-10 micron
Sulfur Dioxide
Carbon Monoxide
Ozone
Nitrogen Dioxide
Lead
Standard
150 g/m3
0.14 PPM
9.0 PPM
0.08 PPM*
0.05 PPM
1.5 g/m3
Time period
24 hour
24 hour
8 hour
1 hour
12 month average
quarterly average
* proposed standard, formally 0.12 parts per million (PPM)
Air Pollutant Emission Standards
In addition to air quality standards, the US air pollution control program consists of identifying
select air contaminants and establishing emission (release) standards. These standards, labeled
National Emission Standards for Hazardous Air Pollutants (NESHAP), set maximum release
limits for select air contaminants and are usually expressed in tons of contaminant emitted per
unit time. Regulation of these emissions is thought to ultimately improve air quality. However,
as can be seen by the Figure 1, the areas of the United States with the greatest emissions do not
necessarily correspond with poor air quality. For example, carbon monoxide emissions are
extremely high in the eastern US, however, the southwest has the most non-attainment counties.
This apparently conflicting relationship is true for ozone, sulfur dioxide and nitrogen dioxide and
reveals the significant impact climate and geography has on air pollution dispersion and
accumulation. However, few air quality specialist disagree that lowering air contaminant
emissions will ultimately improve overall US air quality. In addition to air quality and emission
standards, the US has additional programs to measure and track air quality improvements.
Toxic Release Inventory
In 1986, the Emergency Planning & Community Right-To-Know Act 5 established a program
whereby specific contaminant air, water and land emissions and releases must be reported by all
business on an annual basis. The reports must be completed and sent to US EPA every year and
2
when compiled are released on the internet for community notification and planning purposes. 6
However, given the self-reporting nature of TRI reports, they are often viewed as incomplete
measures of environmental loading.
FIGURE 1: Comparison of Carbon Monoxide Non-Attainment Areas (left) and Location
of Largest Carbon Monoxide Emissions (right)
Shaded areas represent nonattainment (violations) of CO
Shaded areas represent
largest emitters of CO
Pollutant Standards Index
Given the numerous air quality standards and a desire to present a single easy to interpret value
to the media and public, the US EPA created the Pollutant Standards Index.7 This numerical
index, ranging from 0-500, is reported for all metropolitan areas exceeding 200,000 and consists
of all the NAAQS with the exception of lead. The numerical index is then linked to 5 health
ratings that are reported by many news organizations on a daily basis. A rating of 100 means
that one of the 5 NAAQS is at or exceeds its regulatory standard. The PSI and its respective
health ratings translate as follows: <50 = Good, 50-100 = Moderate, 100-200 = Unhealthful, 200300 = Very Unhealthful and over 300 = Hazardous.
B. New York City’s Air Monitoring Program
As with many environmental programs in the US, the Environmental Protection Agency is
permitted to delegate the duties of federal regulations to local state governments. In New York
State, the Department of Environmental Conservation (DEC) has been given the authority to
comply with many US EPA Clean Air Act programs. With regard to air monitoring, the NYS
3
Department of Environmental Conservation is responsible for collecting, analyzing and reporting
ambient air quality, NESHAP, TRI and PSI data. In addition, DEC’s other duties include:
Inspection & Maintenance, Air Research, Air Quality Planning, Air Quality Surveillance,
Regulating Stationary and Mobile Sources, Technical Support and Compliance Monitoring &
Enforcement.
The Department of Environmental Conservation divides New York State into 9 regulatory
regions of which the New York City falls in Region 2. Historically, New York City air pollution
sampling sites have been stationed atop public buildings, usually public schools. Federal
regulations mandate numerous sitting criteria for air monitoring stations.4 Height, distance to
nearest emission sources, obstructions, accessibility and security are just some of the criteria US
EPA mandates in selecting a location.
Air sampling stations in New York City are established for several reasons. The data presented in
this paper comes from compliance sampling stations (i.e. background air levels). However, the
Department of Environmental Conservation has also established numerous air emissions
assessment and air quality research stations. The background or compliance air testing is usually
done in real-time and transmitted electronically to a central DEC office. Presently, real-time air
quality levels for select contaminants can be viewed on the internet.8 The pollutants monitored,
analytical method and location for NYC are presented in Table 2.
TABLE 2: Air Quality Monitoring Stations in New York City (1998)
Number of Sampling Sites
Pollutants Monitored
Sulfur Dioxide
Particulate Matter 10 microns
Total Suspended Particulates
Carbon Monoxide (traffic sites)
Carbon Monoxide (background)
Ozone
Oxides of Nitrogen
Lead
PM10 (sulfates & nitrates)
TSP (sulfates & nitrates)
Analytical Method
Continuous pulsed fluorescence
Wedding or Dichotomous sampler
High volume air sampler
Continuous non-dispersive IR
Continuous non-dispersive IR
Continuous UV light absorption
Continuous chemiluminescence
High volume air sampler
Wedding or Dichotomous sampler
High volume air sampler
Man. Queens Bklyn. Bronx
2
1
2
2
4
0
3
2
1
0
1
0
3
0
1
0
1
1
1
1
0
1
1
2
2
1
1
2
1
0
1
0
3
0
2
0
0
0
1
0
S.I.
1
3
2
0
0
1
0
2
1
0
4
C. New York City Ambient Air Quality Trends – NAAQS
Air quality levels for the 6 ambient standards, sulfur dioxide, particulate matter (10 micron),
carbon monoxide, ozone, oxides of nitrogen and lead have steadily improved over the last 30
years in the New York City.9-11 While at one time the levels routinely exceeded regulatory
limits, today this occurs infrequently and for most of the contaminants, rarely.
Sulfur dioxide levels in NYC continue to be well below the 12 month annual average limit of
0.03 PPM and the 24 hour 0.14 PPM and have changed little during the last few years. In 1998,
no SO2 level exceeded its regulatory limit in NYC. The highest short-term (24 hour average)
level in NYC was measured at the Mabel Dean Station in Manhattan on December 16, 1998 at
0.044 PPM. This value was below its regulatory limit of 0.14 PPM for a 24 hour period. Given
many NYC buildings still use diesel oil as a heating fuel source, SO2 emissions and ambient air
levels are more linked to the numerous small generators found throughout the boroughs. Figure 2
for 10 year SO2 averages by borough. As with all air quality figures presented in this paper, the
borough data is an average of all sampling sites within that borough.
FIGURE 2: Ten Year Sulfur Dioxide Trend (PPM)
0.0500
US EPA Standard 0.14 PPM
0.0400
0.0300
0.0200
0.0100
0.0000
1988 1989 1990 1991 1992 1993 1994 1995 1996 1997 1998
Manhattan
Bronx
Brooklyn
Queens
Particulate Matter (10 micron) also stayed within short term and long term regulatory standards
for 1998. The highest twenty-four hour concentration occurred in Manhattan at the Street
Canyon site on 37th Street on January 5, 1998 (121 ug/m3). Figure 2 represents a 10 year profile
of PM10 by borough.
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FIGURE 3: Ten Year Respirable Particulate (PM10) Trend
100
US EPA Standard - 150 micrograms/m3
80
60
40
20
0
1988 1989 1990 1991 1992 1993 1994 1995 1996 1997 1998
Manhattan
Bronx
Brooklyn
StatenIsld
Even though New York City has maintained carbon monoxide levels far below regulatory
standards, periodic excursions force it to be classified as a non-attainment parameter. The highest
one-hour concentration was recorded on July 22, 1998 in Manhattan at the Bloomingdale’s site
(East 59th Street) and registered 12.5 PPM. Other one-hour concentrations in 1998 ranged from
3.9 to 8.3 PPM. Figure 4 shows the 10 year carbon monoxide trend for NYC boroughs.
FIGURE 4: Ten Year Carbon Monoxide Trend (PPM)
5.0
US EPA Standard - 9 ppm
4.0
3.0
2.0
1.0
0.0
1988 1989 1990 1991 1992 1993 1994 1995 1996 1997 1998
Manhattan
Bronx
Brooklyn
Ozone levels are influenced by numerous other contaminants and atmospheric conditions, most
notably temperature and sunlight. Table 3 highlights this relationship and shows the number of
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exceedances per year with the average number of days over 32.2º C (90º F) that same year. It
becomes apparent that ozone formation is strongly linked to atmospheric conditions. However,
despite this, ozone levels have continued to decrease albeit not as dramatic as other air
parameter.
TABLE 3: Number of Days Ozone Standard Exceedances by Year and Ambient Temperature 11
# Days > 32ºC (90°F)
Year
Ozone Exceedances
(NYC Central Park)
1988*
33
31*
1989
8
16
1990
9
10
1991*
15
31*
1992
2
7
1993*
9
35*
1994
8
18
1995
8
27
1996
4
1
1997
8
12
*meteorological conditions conducive to ozone formation
NYC still has problems meeting the proposed federal ozone standard of 0.08 PPM. The highest
levels seem to ignore geographical barriers and can be found in all boroughs of NYC (i.e. 1 hour
averages: Manhattan 0.125 PPM, Bronx 0.122 PPM, Brooklyn 0.089, Queens 0.142 PPM and
Staten Island 0.138 PPM). Figure 5 presents the 10 year ozone averages by borough.
FIGURE 5: Ten Year Ozone Trend (PPM)
0.080
0.070
0.060
0.050
0.040
0.030
0.020
0.010
0.000
US EPA standard - 0.08 PPM
1988
1989
Manhattan
1990
1991
Bronx
1992
1993
Brooklyn
1994
1995
Queens
1996
1997
1998
Staten Island
7
Nitric oxide and nitrogen dioxide levels continue to be well below the air quality standard of
0.05 PPM (annual average). The highest annual mean level occurred at Public School 59 in
Manhattan (0.040ppm). Figure 6 presents the 10 year nitrogen dioxide averages by borough.
FIGURE 6: Ten Year Nitrogen DioxideTrend (PPM)
0.050
0.040
0.030
US EPA standard - 0.05 PPM
0.020
0.010
0.000
1988
1989
1990
1991
1992
Manhattan
1993
Bronx
1994
1995
1996
1997
1998
Brooklyn
Finally, airborne lead levels have been consistently below the national ambient air quality
standard of 0.15 ug/m3 and have remained stable for the past 10 years. Given the insignificant
change, lead levels will not be reported here.
D. New York City Pollutant Standards Index Trends
As stated earlier, the Pollutant Standards Index (PSI) is standardized value that allows for
simplified comparisons of air quality levels regardless of measurement units.7 A PSI of 100
indicates the air parameter has reached its regulatory standard. Figures 7, 8 and 9 present the PSI
for 1979, 1989 and 1999 for the major air quality parameters respectively. A comparison of 3
decades worth of PSI values clearly reveals the tremendous improvements in air quality for the
New York City region. In 1979 air quality in New York City consistently ranked in the
moderate to unhealthful zone for all contaminants. Periodically during 1979, the PSI for ozone
and carbon monoxide reached “very unhealthful” levels. In 1999, conditions changed
significantly. The PSI for carbon monoxide and sulfur dioxide never reached “moderate” and
8
were consistently rank as “good”. The only continuing problem in New York City’s air is ozone.
This parameter exceeded its PSI on 9 separate days in 1998. Most excursions, none of which
exceeded a PSI of 170, occurred in the summer months where intense sunlight and high
temperature stimulated ozone production. It is clear from Figures 7, 8 and 9 that New York
City’s air quality has been significantly affected during the last 30 years. These improvements
seem to be continuing into the future.
FIGURE 7: Pollutant Standards Index 1979
9
FIGURE 9: Pollutant Standards Index 1989
FIGURE 8: Pollutant Standards Index 1999
10
E. Monitoring for Toxics in New York City Air
In addition to the 6 ambient air quality standards, New York State established a program to
monitor for select hazardous organic volatile air pollutants.12 Two air monitoring stations, one in
Brooklyn the other in Staten Island monitor ambient air for 18 individual volatile organic
compounds. In addition, given community environmental health concerns adjacent to the
world’s largest landfill located in Staten Island, additional stations have been established in the
vicinity of the landfill. As with all solid waste landfills, off-gassing of decomposition byproducts and waste gases continue despite significant reductions in waste disposal. Monitoring
the adjacent neighborhood air quality is an effort to evaluate landfill discharges and assess health
risks.
Table 4 presents the volatile organic chemical data for 1998 for the Brooklyn air sampling
station. The highest values however were discovered either on or adjacent to the solid waste
landfill in Staten Island. The NY State Department of Environmental Conservations guideline
values stated in column one, are adapted from published occupational health values.
TABLE 4: Average Annual Concentrations and Maximum Values of
Volatile Organic Chemicals in NYC Air – 1998 (parts per billion)
NY State DEC
Guideline (ppb)
Methylene Chloride
7.8
Chloroform
4.7
1,2, Dichloroethane
0.01
1,1,1 Trichloroethane
183.0
Carbon Tetrachloride
0.01
Trichloroethylene
0.08
1,1,2 Trichloroethane
0.01
Tetrachloroethylene
0.18
Benzene
0.04
Toluene
532.0
Ethylbenzene
230.0
M,P-Xylene
69.1
O-Xylene
161.0
Chlorobenzene
4.3
O-Dichlorobenzene
33.3
M-Dichlorobenzene
33.3
P-Dichlorobenzene
116
Vinyl Chloride
-
Average Conc.
Highest
Brooklyn Station 24 hr Value
0.19
5.30
0.01
0.05
0.01
0.02
0.03
0.49
0.03
0.08
0.05
0.30
0.02
0.02
0.22
1.64
0.25
0.96
1.36
12.44
0.18
1.21
0.59
3.39
0.21
0.95
0.01
0.08
0.01
0.03
0.02
*
0.07
0.68
0.04
0.38
Location of
Highest Value
Staten Island
Staten Island
Staten Island
Staten Island
Staten Island
Staten Island
*
Brooklyn
Staten Island
Staten Island
Staten Island
Staten Island
Staten Island
Staten Island
Staten Island
*
Staten Island
Staten Island
* at or below detectable limit
11
As can be seen from the data, the majority of volatile organic chemicals are within these
guidelines. However, New York City air continues to have elevated levels of the leukemogen,
benzene. This compound, together with toluene, ethylbenzene and xylenes, are common
constituents of gasoline and still find their way into New York City air via automotive
evaporation pathways and tank refueling leaks.
F. Successes
Carbon Monoxide:
The sustained improvement in carbon monoxide levels has been attributed to several factors
related to specific regulatory programs. Generally, the greatest benefit resulted from the steady
turnover of older, high polluting cars and trucks. Modern day passenger vehicles emit far less
contaminants than those purchased just 5 years earlier and significantly less than vehicles of the
1970’s. Another major factor is the steady change-over to compressed natural gas (CNG) driven
vehicles. The NYC taxi fleet, the local power and telephone utilities together with the private
and public transportation bus fleets has all adopted program to change a percentage of their fleets
to CNG vehicles.
A third major initiative that caused air quality improvements was transportation fuel
improvements and modifications such as the oxygenated fuel changeover program during winter
months. While a controversial environmental issue (the prime oxygenated additive, Methyl
Tertiary Butyl Ether, has been implicated in groundwater contamination and its addition to
gasoline temporarily halted), the additive, comprising up to 2.7% by weight of gasoline, helps to
oxidize carbon monoxide to carbon dioxide and hydrocarbons to water and CO2 thereby reducing
CO emissions and reducing ozone formation. Additional fuel alterations such as summer
gasoline volatility limits and reformulated gasoline, will likely generate even further air quality
improvements. For example, in 1989 gasoline sold during the summer months must have a Reid
Vapor Pressure (RVP) of no more than 9.0 PSI (pounds per square inch) which substantially
lowers evaporative releases.
Finally, the NY metropolitan area (New Jersey, New York and Connecticut) has advance
inspection and maintenance programs to ensure automotive pollution controls are being
maintained appropriately. Such programs are also being implemented for buses, trucks and other
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commercial vehicles and are likely to continue air quality improvements in carbon monoxide and
ozone.
Ozone
As can be seen from data presented above, the New York Metropolitan area continues to have
problems with ozone. Given the relationship and photochemistry between ozone, carbon
monoxide and hydrocarbons, added reductions in CO emissions will also improve ozone levels.
However, as stated earlier, ground level ozone formation is strongly dependent on atmospheric
conditions such as sunlight and temperature and tends to be seasonally related.
Sulfur Dioxide
Sulfur dioxide levels have dropped continuously since implementation of strict sulfur in fuel oil
requirements came into place in the 1970’s. Improvements in coal and oil desulfurization has
contributed to the reduction of sulfur in home heating oil with subsequent air quality benefits.
Reduction in emissions can also be attributed to regulatory program targeted to specific
industrial processes where SO2 is generated.
The improved engine designs, catalytic converters, control of fugitive emissions, and extensive
inspection and maintenance programs have also triggered reductions in particulate matter, oxides
of nitrogen and lead.
G. The Future
New regulatory and public health initiatives center on further improvements in air quality and
overall reductions in air emissions. In addition to preventing ozone precursors from entering the
ambient air, the US Environmental Protection Agency together with public health activist groups
are pursuing the following.

PM2.5 and ultra-fine particulates– Recent studies have shown that very small particulate
matter (< 2.5 micron) especially those found in diesel exhausts, may play a significant
role in asthma and other respiratory diseases. Future regulatory standards may be
generated for this category of pollutant.
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
SO2 and Acid Rain Controls– While overall sulfur dioxide air levels are significantly
lower, the overall emissions (release into the atmosphere) still remain high. Given the
ecological impact of SO2 , the US EPA has initiated a program whereby emissions will be
substantially reduced by 2010. The program has received significant attention and
criticism given its innovative market based approach (ie. the selling air pollution credits).

VOCs – Recent initiatives in regulating hazardous air emissions such as volatile organic
chemicals is likely to be expanded. Many of these chemicals have chronic health effects
and some present human cancer risks. Development of alternative, non-organic solvent
based residential and commercial paints as stimulated by the Pollution Prevention Act 13,
is an example of one of the primary prevention approaches being implemented. Research
and development of alternative dry cleaning solvents, glues and adhesives, are all
intended to reduce emissions from VOCs.
While the major ambient air quality pollutants identified in the early 1970’s have been
addressed and essentially controlled to previously defined limits (with the exception of
ozone), the US continues to develop long term air quality goals which target aesthetic,
ecological and human health concerns. Industry resistance to new initiatives also remains
constant with many asking; “when will it end”. Improving US environmental quality is a
common goal that straddles political and social agendas and in trickles down to individual
desires. While zero-emissions of air contaminants may seem an unachievable goal; it is a
goal that many in government and the community see as worthy of pursuit.
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REFERENCES
1.
Clean Air Act (CAA); 42 U.S.C. s/s 7401 et seq. 1970
2.
The National Ambient Air Quality Standards, US Environmental Protection Agency,
www.epa.gov/air, Washington DC, 2000
3.
Evaluating Exposures to Toxic Air Pollutants: A Citizen's Guide, US Environmental
Protection Agency, Washington DC, EPA 450/3-90-024, 1999
4.
Probe and Monitoring Sitting Criteria for Ambient Air Quality Monitoring. 40 Code of
Federal Regulations 40 CFR 58 Appendix E: Washington DC, 1999
5.
Emergency Planning & Community Right-To-Know Act (EPCRA); 42 U.S.C. 11011 et seq.
1986
6.
Toxic Release Inventory, US Environmental Protection Agency, www.epa.gov/tri,
Washington DC, 2000
7.
The Pollutant Standards Index, Office of Air Quality Planning and Standards,
Environmental Protection Agency, 451/K-94-001, Washington, DC, 1994
8.
NYS Ambient Air Monitoring System: Near Real Time Data, Division of Air Resources,
Bureau of Technical Support, New York State Department of Environmental Conservation,
www.dec.state.ny.us/website/dar/bts/airmon/index.htm, May 2000
9.
National Air Quality and Emissions Trends Report; Office of Air Quality Planning and
Standards, US Environmental Protection Agency, Research Triangle Park, NC 454/R-00003, March 2000
10.
Ambient Air Quality Report – 1998, New York State Department of Environmental
Conservation, Division of Air Resources Albany, NY 2000
11.
Compliance and Enforcement Summary Annual Report for Federal Fiscal Year 1998-1999,
New York State Department of Environmental Conservation, Division of Air Resources
Albany, NY 1999
12.
Ambient Air Monitoring Report for Volatile Organic Compounds (Summary of Toxic
Monitoring Data from 1990 to 1993), Division of Air Resources, New York State
Department of Environmental Conservation, Albany, NY 1999
13.
The Pollution Prevention Act. 42 U.S.C. 13101 and 13102, s/s et seq. 1990
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