**United States En**  **vir onmental Pr**  **otection Ag**  **enc y**  

# Latest Findings on National Air Quality

**2001 ST A**  **TUS AND TRENDS**Cov er Photo of Mount McKinle y

, Denali National P ark, Alaska, b y Kim F erguson, W a ynesville , Nor th Car olinaEPA 454/K-02-001 September 2002



# Latest Findings on National Air Quality

**2001 STATUS AND TRENDS**

Contract No. GS-10F-0283K

T

ask Order No. TO 1307

U. S. Environmental Protection Agency Office of Air Quality Planning and Standards Emissions, Monitoring, and Analysis Division Research Triangle Park, North Carolina

### Contents

**National Air Quality . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 Six Principal Pollutants. . . . . . . . . . . . . . . . . . . . . . . . . . 3**  **Acid Rain. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16 V**  **isibility . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18 T** 

**oxic Air Pollutants. . . . . . . . . . . . . . . . . . . . . . . . . . . . 20 Stratospheric Ozone. . . . . . . . . . . . . . . . . . . . . . . . . . . 23**  **Conclusions. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25 Acronyms . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26** 

More detailed information on air pollution trends is available at **www.epa.gov/airtrends**

. Information on global warming and global climate change is available at **www .epa.gov/globalwarming/publications/emissions**  and **www .epa.gov/globalwarming/publications/car** 
**.**EP A tracks air pollution in two ways:
• Air quality measured

from over 3,000 locations (over 5,200 monitors) across the nation operated primarily by state, local, and tribal agencies. • E missions from all

sources going back 30 years.

**1** ■ EP A, states, and tr ibes ha v e only r ecently begun to measur e fine par ticles (known as PM 2.5 ) in the air on a br oad national basis. In man y locations, EP A now has 3 y ear s of air quality monitor ing data to use in compar ing to the health-based standards for PM 2.5 . Based on those data, ar eas acr oss the Southeast, Mid-Atlantic , a nd Midwest r e g ions and Califor nia ha v e air quality that is unhealth y due to fine par ticles. High PM concentrations in the easter n United States ar e due to re g ional emissions fr om po wer plants and motor v ehicles in combination with local emissions fr om transpor tation and other sour ces. In Califor nia, high PM concentrations tend to be due to mobile sour ce emissions.
■ Of the six track ed pollutants, pr o g r ess has been slowest for g r ound-le v el ozone

. The Nor theast and W est exhibited the g r eatest impr ov ement, while the South and Nor th Central r e g ions exper ienced slower pr o g r ess in lowe r ing ozone concentrations. Despite this pr o g r ess in most re g ions of the countr y , the a v erage ozone (8-hour) le v els in 33 of our national parks ha v e incr eased ov er the past 10 y ear s.
■ Gr ound-le v el ozone is not emitted dir ectly into the air b ut is for med in the atmospher e by the r eaction of volatile organic compounds (VOCs) and nitr o gen oxides (NO x ) in the pr esence of heat and sunlight. Although emissions of VOCs ha v e decr eased 16 per cent ov er the past 20 year s, the lack of significant r eductions in r e g ional-scale emissions of NO x , a f amily of chemicals that can contr ib ute to the for mation of ozone hundr eds of miles downwind, has slowed pr o g r ess in r educing ozone le v els. Between 1982 and 2001, NO x emissions in the United States incr eased 

# National Air Quality
This summar y repor t highlights the U

. S

. Environmental Protection Agency’ s (EP A’ s) most recent ev aluation of the status and trends in our nation’ s air quality

.

**Highlights**

■ Since 1970, agg r egate emissions of the six

pr incipal pollutants track ed nationally ha v e been cut 25 per cent. Dur ing that same time per iod, U

. S

. g r oss domestic pr oduct incr eased 161 per cent, energy consumption incr eased 42 per cent, and v ehicle miles tra v eled incr eased 149 per cent.
■ National air quality le v els measur ed at thousands of monitor ing stations acr oss the countr y ha

v e shown impr ov ements ov er the past 20 year s for all six pr incipal pollutants.

■ Despite this pr o g r ess, almost 170 million tons of pollution ar e emitted into the air each year in the United States, and appr o x imately 133 million people li v e in counties wher e monitor ed air in 2001 was unhealth y at times because of high le v els of at least one of the six pr incipal air pollutants.

■ The vast major ity of ar eas that exper ienced

unhealth y air did so because of one or both of tw o pollutants—ozone and par ticulate matter (PM). EP A is focusing its effor ts to contr ol these pollutants b y implementing mor e str ingent National Ambient Air Quality Standards for ozone and PM and r ules r educing emissions fr om on-r oad transpor tation and stationar y comb ustion sour ces. These r ules will br ing r eductions in emissions ov er the next fe w year s. Additional r eductions will be needed to pr ovide clean air in the futur e . EP A has submitted to Cong r ess Clear Skies leg islation that, if enacted, w ould mandate r eductions of par ticle- and ozone- for ming compounds fr om power generator s b y 70 per cent fr om cur r ent le v els through a nationwide cap and trade pr o g ram. E P A

also expects to pr opose nonr oad v ehicle r egulations that w

ould help impr ov e ozone and PM air quality

.**2**National AirQuality

9 per cent (with a 3 per cent decr ease in the past 10 year s). The major ity of this incr ease is attr ib uted to g r owth in emissions fr om nonr oad eng ines (lik e constr uction and r ecr eation equipment) and diesel v ehicles. Emissions of NO x also contr ib ute to acid rain, haze , par ticulate matter , and damage to waterbodies lik e the Chesapeak e Ba y

. ■ Sulf ates for med pr imar ily fr om sulfur dioxide (SO 2 ) emissions fr om coal-fir ed power plants ar e a major component of fine par ticles in the easter n United States. SO 2 emissions decr eased 25 per cent fr om 1981 to 2001 and 24 per cent fr

om 1992 to 2001. Nationally , a

v erage SO 2 ambient concentrations ha v e been cut 52 percent fr om 1982 to 2001 and 35 per cent ov er the mor e r ecent 10-year per iod fr om 1992 to 2001. Reductions in SO 2 concentrations and emissions since 1990 ar e pr imar ily due to contr ols implemented under EP A’

s Acid Rain Pr o g ram.
■ Based on EP A’

s r ecent National-Scale Air Toxics Assessment for 1996, 3 of 32 urban air toxics (chr omium, a metallic compound used in industr ial pr ocesses such as plating; benzene , pr imar ily emitted b y mobile sour ces such as

0 20 40 60 80 100 120 140

CO (-19%) NO x (+15%) VO C (-38%) SO 2 (-44%) PM 10 (-76%) 0 50 100 200 250

150

Pb (-98%) 1970 2001Million tons **Comparison of 1970 and 2001 Emissions**Thousand tons **Six Principal Air Pollutants T racked Nationally** 

■ Nitrogen Dioxide (NO 2 )
■ Ozone (O 3 ) - formed by volatile organic compounds (VOCs) and nitrogen oxides (NO x )
■ Sulfur Dioxide (SO 2 )
■ Particulate Matter (PM) - formed by SO 2 , NO x , ammonia, VOCs, and direct particle emissions
■ Carbon Monoxide (CO)
■ Lead (Pb) car s and tr ucks; and for maldeh yde , e mitted by mobile sour ces and for med when other compounds chemically r eact in sunlight) appear to pose the g r eatest nationwide cancer r isk. One air toxic , acr olein — a b y pr oduct of comb ustion in mobile and industr ial sour ces — is estimated to pose the highest potential on a nationwide basis for significant chr onic adv er se effects other than cancer

. ■ Scientific e vidence sho ws that the Montr eal

Pr

otocol has been effecti v e in r educing stratospher ic ozone depletion. Measur ements ha v e shown that atmospher ic concentrations of meth yl chlor ofor m ar e f alling, indicating that emis sions ha v

e been g r eatly r educed. Concentrations of other ozone-depleting substances in the upper la ye r s of the atmospher e , lik e chlor ofluor ocarbons (CFCs), ar e also beg inning to decr ease . **Air Pollution** The Concer n The a v erage per son br eathes 3,400 gallons of air each da y

. Exposur e to air pollution is associated with n umer ous effects on human health, including r espirator y pr ob lems, hospitalization for hear t or lung diseases, and e v en pr ematur e death. Childr en ar e at g r eater r isk because the y ar e generally mor e acti v e outdoor s and their lungs ar e still de v eloping. The elderly and people with hear t or lung diseases ar e also mor e sensiti v e to some types of air pollution.Air pollution can also significantly affect ecosystems. F or example , g r ound-le v el ozone has been estimated to cause ov er $500 million in ann ual r eductions of ag r icultural and commer cial for est yields, and airbor ne r eleases of NO x ar e one of the largest sour ces of nitr o gen pollution in cer tain water-bodies such as the Chesapeak e Ba y

. The Causes Air pollution comes fr om man y differ ent sour ces. These include stationar y sour ces such as f actor ies, po wer plants, and smelter s; smaller sour ces such as dr y cleaner s and deg r easing operations; mobile sour ces such as car s, b uses, planes, tr ucks, and trains; and natural sour ces such as windb lown dust and wildfir es.**3** 

# Six Pr incipal P ollutants

sulfur dioxide (SO 2 ), par ticulate matter (PM), carbon monoxide (CO), and lead (Pb). F our of these pollutants (CO , P b , NO 2 , and SO 2 ) r esult pr imar ily fr om dir ect emissions fr om a va r iety of sour ces. PM r esults fr om dir ect emissions, b ut is also commonly for med when emissions of nitrogen oxides (NO x ), sulfur oxides (SO x ), ammonia, organic compounds, and other gases r eact in the atmospher e . Ozone is not dir ectly emitted b u t is for med when NO x and volatile organic compounds (VOCs) r eact in the pr esence of sunlight. Each year EP A examines changes in le v els of these ambient pollutants and their pr ecur sor emissions ov er time and summar izes the cur r ent air pollution status. **Summary of Air Quality and Emissions Tr**  **ends** EP A tracks tr ends in air quality based on actual measur ements of pollutant concentrations in the ambient (outside) air at monitor ing sites acr oss the countr y . Monitor ing stations ar e operated b y state , tr ibal, and local gov e r nment agencies as well as some federal agencies, including EP A. T r ends ar e der i v ed b y a

v erag ing dir ect measur ements fr om these monitor ing stations on a yearly basis. The tab les to the left show that the air quality based on concentrations of the pr incipal pollutants has impr ov ed nationally ov er the past 20 y ear s (1982–2001). EP A estimates nationwide emissions of ambient pollutants and their pr ecur sor s based on actual monitor ed r eadings or eng ineer ing calculations of the amounts and types of pollutants emitted by v ehicles, f actor ies, and other sour ces. Emission estimates ar e based on man y

f

actor s, including the le v el of industr ial acti vity , technolo gy de v elopments, fuel consumption, v ehicle miles tra v eled, and other acti vities that cause air pollution. 

## Under the Clean Air Act, EPA establishes air quality standards to pr otect pub lic health, including the health of “sensiti v e ” p opulations such as people with asthma, childr en, and the elderly

. E P A

also sets limits to pr otect pub lic welf ar e , including pr otection against decr eased visibility and damage to animals, cr ops, v egetation, and b uildings. EP A has set national air quality standards for six pr incipal air pollutants (also r efer r ed to as cr iter ia pollutants): nitr o gen dioxide (NO 2 ), ozone (O 3 ), 

# NO 2 

# O 3 

# SO 2 

# PM CO Pb

**Per cent Change in Air Quality** 

**1982-2001 1992-2001**  NO 2 -24 -11 O 3 1-h -18 -3 8-h -11 0 SO 2 -52 -35 PM 10 — -14 PM 2.5 Tr end data not a v aila b l e CO -62 -38 Pb -94 -25

**Per cent Change in Emissions**  **1982-2001 1992-2001**  NO x +9 -3 VO C -16 -8 SO 2 -25 -24 PM 10 * -51 -13 PM 2.5 * -10 CO 0 + 6 Pb -93 -5 *Includes only dir ectly emitted par ticles. Negativ e numbers indicate improv ements in air quality or reductions in emissions

. Positiv e numbers show where emissions hav e increased

. Air quality concentr ations do not alw ays tr ac k nationwide emissions

. There are sev er al reasons for this

. First, most monitors are located in urban areas so air quality is most likel y to tr ac k c hanges in urban air emissions r ather than in total emissions

. Second, not all of the pr incipal pollutants are emitted directl y to the air

. O z one and many par tic les are for med after directl y emitted gases react c hemicall y to for m them. Thir d, the amount of some pollutants measured at monitor ing locations depends on the c hemical reactions that occur in the atmosphere dur ing the time it takes the pollutant to tr av el from its source to the monitor ing station. Finall y , weather conditions often contr ib ute to the for mation and b uildup of pollutants in the ambient air

. For example , peak oz one concentr ations typicall y occur dur ing hot, dr y stagnant summer time conditions

. —**4**Six Principal Pollutants

-50% 0% 50% 100% 150% 200%

**70 01**  **161%**
**149%**

**42% 39%** 

**-25% Comparison of Gr**  **o wth Areas and Emissions** 

**95 80**  **90 96**  **97 98**  **99 00**  Agg regate Emissions (Six Pr incipal P ollutants) Gross Domestic Product

V

ehicle Miles T r a v eled

Energy Consumption

U. S. P opulation

Between 1970 and 2001, gross domestic product increased 161 percent, v ehic le miles tr av eled increased 149 percent, energ y consumption increased 42 percent, and U

. S

. population increased 39 percent. At the same time , total emissions of the six pr incipal air pollutants decreased 25 percent.

Emission estimates also r eflect changes in air pollution r egulations and installation of emission contr ols. The 2001 emissions r epor ted in this summar y ar e pr ojected n umber s based on a vailab le 2000 infor mation and histor ical tr ends. Emission estimation methods contin ue to e volv e and impr ov e ov er time

. Methods ha v e changed for man y significant categor ies beg inning with the year s 1985, 1990, and 1996, and, consequently , the estimates ar e not consistently de v eloped acr oss all y ear s in this tr end per iod. Because emissions estimation methods for man y significant categor ies ha

v e changed ov er time , compar isons of the estimates for a g i v en y ear in this r epor t to the same year in a pr e vious r epor t ma y not be appr opr iate

. Check www .epa.g o v/ttn/chief for updated emissions infor mation.**5** Emissions of all pr incipal pollutants except NO x ha

v e decr eased or r e mained essentially unchanged ov er the past 20 year s (1982–2001), while all air quality measur es for the six pr incipal pollutants ha

v e gone down. Although NO x emissions ha v e incr eased, air quality measur ements for NO 2 acr oss the countr y ar e below the national air quality standards. NO x pla ys an impor tant r ole in a n umber of air pollution issues. These compounds contr ib ute to the for mation of ozone and par ticles as well as the deposition of acids and n utr ients and visibility impair ment. The impr ov ements ar e a r esult of effecti v e implementation of clean air la ws and r egulations, as well as impr ov ements in the efficiency of industr ial technolo g ies. Despite g r eat pr o g r ess in air quality impr ov ement, appr oximately 133 million people nationwide still li

v

ed in counties with pollution le v els abo v

e the National Ambient Air Quality Standards (NAA QS) in 2001. This ann ual “snapshot” vie w of the nation’ s air quality can be used to show le v els that people might cur r ently be exper iencing acr oss the county
. Ther e ar e still 130 nonattainment ar eas out of the 230 or ig inally r esulting fr om the 1990 Clean Air Act Amendments designation pr ocess. **The Clean Air Act** The Clean Air Act pr ovides the pr incipal framew

ork for national, state , t r ibal, and local effor ts to pr

otect air quality

. Under the Clean Air Act, EP A has a n umber of r esponsibilities, including

■ Setting NAA QS for the six pr incipal pollutants that ar e consider ed har mful to pub lic health and the en vir onment.
■ Ensur ing that these air quality standards ar e

met (in cooperation with the state , t r ibal, and local gov e r nments) thr ough national standards and strateg ies to contr ol air pollutant emissions fr

om v ehicles, f actor ies, and other sour ces.
■ Reducing emissions of SO 2 and NO x that cause acid rain.

■ Reducing air pollutants such as PM, SO x , and NO x that can cause visibility impair ment acr oss large r e g ional ar eas, including man y of the nation’ s most tr easur ed parks and wilderness ar eas.
■ Ensur ing that sour ces of to xic air pollutants that ma y cause cancer and other adv er se human health and en vir onmental effects ar e well contr olled and that the r isks to pub lic health and the en vir onment ar e substantially r educed.

■ Limiting the use of chemicals that damage the stratospher ic ozone la yer in order to pr e v ent incr eased le v els of har mful ultra violet radiation.Six Principal Pollutants

110.3 (8-hour)

0 0 100 150

0.007
11.1
72.7
0.7
2.7
133.1 40.2 (1-hour) 0

Millions of P eople **Number of P eople Living in Counties**  **with Air Quality Concentrations abo ve**  **the Le vel of the NAA**  **QS in 2001**

Multiple y ears of data are gener all

y used to deter mine if an area attains the NAA QS

. 5 NO 2

O 3

SO 2 PM 10 PM 2.5

CO
Pb
An y NAA QS**6**Six Principal Pollutants **NITROGEN DIOXIDE (NO 2**  **)**Thousand ShortTonsConcentration, ppm **Natur e and Sour**  **ces of the Pollutant** Nitr o gen dioxide is a r eddish br o wn, highly r eacti

v e gas that is for med in the ambient air thr ough the oxidation of nitr ic oxide (NO). Nitr o gen oxides (NO x ), the ter m used to descr ibe the sum of NO , N O 2 , and other oxides of nitr o gen, pla y a major r ole in the for mation of ozone , par ticulate matter , haze , and acid rain. While EP A tracks national emissions of NO x , t h e national monitoring netw ork measur es ambient concentrations of NO 2 for compar ison to national air quality standards. The major sour ces of man-made NO x emissions ar e high-temperatur e comb ustion pr ocesses, such as those that occur in automobiles and po we r **NO 2**  **Air Quality ,**  **1982–2001** Based on Ann ual Ar ithmetic A v er age
0.06
0.05
0.04
0.03
0.02
0.01
0.00 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 00 01 **NAA QS**  121 Sites

10% of sites ha v e concentr ations belo w this line 90% of sites ha v e concentr ations belo w this line

Av e r age

**1982–01: 24%**  **decrease 1992–01:**  **11% decrease**  Air quality concentr ations do not alw ays tr ac k nationwide emissions

. For a detailed explanation, see page 3. **NO x**  **Emissions, 1982–2001** 
Fuel Comb ustion Industr ial Processes Tr anspor tation Miscellaneous 30,000
25,000
20,000
15,000
10,000
5,000 In 1985, EP A refined its methods f or estimating emissions

.

0 82 85 92 93 94 95 96 97 98 99 00 01 **1982–01: 9%**  **increase 1992–01:**  **3% decrease**  plants. Home heater s and gas stov es can also pr

oduce substantial amounts of NO 2 in indoor settings. **Health and Envir onmental Ef**  **fects** Shor t-ter m exposur es (e .g., less than 3 hour s) to low le v els of NO 2 ma y lead to changes in airwa y r esponsi v eness and lung function in indi viduals with pr eexisting r espirator y illnesses and incr eases in r espirator y illnesses in childr en. Long-ter m exposur es to NO 2 ma y lead to incr eased susceptibility to r espirator y infection and ma y cause ir r e
ve r sib le alterations in lung str uctur e . NO x r eacts in the air to for m g r ound-le v el ozone and fine par ticle pollution, which ar e both associated with adv er se health effects. NO x contr ib utes to a wide range of en vir onmental effects dir ectly and/or when combined with other pr ecur sor s in acid rain and ozone (see en vironmental discussion under Ozone and Acid Rain). Nitr o gen inputs to ter r estr ial and wetland systems can alter existing competiti v e r elationships among plant species, leading to changes in community composition and di v e r sity

. Similarly , dir ect nitr o gen inputs to aquatic ecosystems such as those found in estuar ine and coastal water s (e .g., Chesapeak e Ba y) can lead to eutr ophication (a condition that pr

omotes excessi v e algae g r o wth, which can lead to a se v e r e depletion of dissolv ed oxygen and incr eased le v els of to xins har mful to fish and other aquatic life). Nitr o gen, alone or in acid rain, also can acidify soils and surf ace water s. Acidification of soils causes the loss of essential plant n utr ients and incr eased le v els of solub le alumin u m that ar e toxic to plants. Acidification of surf ace water s cr eates conditions of lo w pH and le v els of alumin um that ar e to xic to fish and other aquatic organisms. Finally , N O x is a contr ib utor to visibility impairment. **Tr ends in NO**  **2 Levels and NO**  **x Emissions**  Ov er the past 20 year s, monitor ed le v els of NO 2 ha

v e decr eased 24 per cent. All ar eas of the countr y that once violated the NAA QS for NO 2 now meet that standar d. While air quality le v els of NO 2 ar

ound urban monitor s ha v e f allen, national emissions of NO x ha v e actually incr eased ov er the past 20 y ear s b y 9 per cent. This incr ease is the r esult of a n u mber of f actor s, the most significant being an incr ease in NO x emissions fr om nonr oad eng ines and diesel v ehicles. This incr ease is of concer n because NO x emissions contr ib ute to the for mation of g r ound-le v el ozone (smo g), b ut also to other en vir onmental pr ob lems lik e acid rain and nitr o gen loadings to waterbodies.**7**Six Principal Pollutants **Natur e and Sour**  **ces of the Pollutant** Gr ound-le v el ozone (the pr imar y constituent of smo g) contin ues to be a pollution pr ob lem thr oughout man y ar eas of the United States. Ozone is not emitted dir ectly into the air b ut is for med b y the r eaction of VOCs and NO x in the pr esence of heat and sunlight. Gr ound-le v el ozone for ms r eadily in the atmospher e , usually dur ing hot summer weather

. VOCs ar e emitted fr om a va r iety of sour ces, including motor v ehicles, chemical plants, r efiner ies, f actor ies, consumer and commercial pr oducts, and other industr ial sour ces. NO x is emitted fr om motor v ehicles, po wer plants, and other sour ces of comb ustion. Chang ing weather patter ns contr ib ute to yearly differ ences in ozone concentrations fr om r e g ion to r e g i on. Ozone and the pollutants that for m ozone also can be transpor ted into an ar ea fr om pollution sour ces found hundr eds of miles upwind. **Health and Envir onmental Ef**  **fects** Shor t-ter m (1- to 3-hour) and pr olonged (6- to 8-hour) exposur es to ambient ozone ha v e been link ed to a n umber of health effects of concer n. F or example , h ealth effects attr ib uted to ozone exposur e include significant decr eases in lung function and incr eased r espirator y symptoms such as chest pain and cough. Exposur es to ozone can mak e people mor e susceptib le to r espirator y infection, r esult in lung inflammation, and agg ravate pr eexisting r espirator y diseases such as asthma. Also , incr eased hospital admissions and emergency r oom visits for r espirator y pr ob lems ha v e been associated with ambient ozone exposur es. These effects generally occur while indi viduals ar e acti v ely ex er cising, w orking, or pla ying outdoor s. Childr en, acti v e outdoor s dur ing the summer when ozone le v els ar e at their highest, ar e most at r isk of exper iencing such effects. Other at-r isk gr

oups include adults who ar e acti v e outdoor s (e .g., some outdoor w ork er s) and indi viduals with pr eexisting r espirator y disease such as asthma and chr onic obstr ucti v e pulmonar y disease

. In addition, longer-ter m exposur es to moderate le v els of ozone pr esent the possibility of ir r e v e r sib le changes in the lung str uctur e , which could lead to pr ematur e ag ing of the lungs and w o r sening of chr onic r espirator y illnesses. Ozone also affects v egetation and ecosystems, leading to r eductions in ag r icultural crop and commer cial for est yields, r educed g r o wth and sur vivability of tr ee seedlings, and incr eased plant susceptibility to disease , pests, and other en vir onmental str esses (e .g., har sh weather). In long-li v ed species, these effects ma y become e vident only after se v eral year s or e v en decades, thus ha ving the potential for long-ter m effects on for est ecosystems. Groundle v e l ozone damage to the foliage of tr ees and other plants can also decr ease the aesthetic value of or namental species as well as the natural beauty of our national parks and r ecr eation ar eas. **GROUND-LEVEL OZONE (O 3**  **)**

Air quality concentr ations do not alw ays tr ac k nationwide emissions

. For detailed explanation, see page 3. 82 85 92 93 94 95 96 97 98 99 00 01 VOC Emissions, 1982–2001

In 1985, EP A refined its methods f or estimating emissions

.

**1982–01: 16%**  **decrease 1992–01:**  **8% decrease**  Fuel Comb ustion Tr anspor tation Industr ial Processes MiscellaneousOzone occurs naturally in the stratosphere and provides a protective layer high above the Earth. See page 23 for more information on the stratospheric ozone layer

.

30,000
25,000Thousand ShortTons 20,000
15,000
10,000
5,000

0**8**Six Principal PollutantsConcentration, ppmConcentration, ppm 0.20

0.15

0.10

0.05

0.00 **Tr ends in Ozone Levels and Related**  **Emissions** In 1997, EP A r e vised the NAA QS for ozone b y setting ne w 8-hour 0.08-ppm standards. Cur r ently , EP A is tracking tr ends based on both 1-hour and 8-hour data. Ov er the past 20 year s, national ambient ozone le v els decr eased 18 per cent based on 1-hour data and 11 per cent based on 8-hour data. Between **Ozone Air Quality ,**  **1982–2001** Based on Ann ual 4th Maxim um 8-Hour A v er age

**NAA QS** 

10% of sites ha v e concentr ations belo w this line Av e r age 379 Sites

90% of sites ha v e concentr ations belo w this line

82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 00 01 **1982–01: 11%**  **decrease 1992–01:**  **0% c**  **hang e** 
Air quality concentr ations do not alw ays tr ac k nationwide emissions

. For a detailed explanation, see page 3.
**Ozone Air Quality ,**  **1982–2001** Based on Ann ual 2nd Maxim um 1-Hour A v er age
0.20

0.15

0.10

0.05

0.00 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 00 01 379 Sites

10% of sites ha v e concentr ations belo w this line 90% of sites ha v e concentr ations belo w this line

Av e r age **NAA QS**  1982 and 2001, emissions of VO Cs decr eased 16 per cent. Dur ing that same time per iod, emissions of NO x incr eased 9 per cent. F or the per iod 1982 to 2001, the downward tr end in 1-hour ozone le v els seen nationally is r eflected in e v er y br oad geo g raphic ar ea in the countr y . The Nor theast and W est exhibited the most substantial impr ov ement, while the South and Nor th Central r e g ions exper ienced the least rapid pr o g r ess in lo we r ing ozone concentrations. Similar to the 1-hour ozone tr ends, all r e g ions exper ienced impr ov ements in 8-hour ozone le v els between 1982 and 2001 except the Nor th Central re gi on, which showed little change dur ing this per iod. Again, the W est and Nor theast ha v e exhibited the most substantial r eductions in 8-hour ozone le v els for the past 20 year s. Acr oss the countr y , the highest ambient 1-hour ozone concentrations ar e typically found at sub u rban sites, consistent with the downwind transpor t of emissions fr om urban center s. Dur ing the past 20 year s, ozone concentrations decr eased appr ox imately 20 per cent at urban and sub urban sites. In the past 10 year s, urban sites sho w declines of appr o ximately 5 per cent and sub urban sites show a 6 per cent decr ease . H o we v e r , at r ural monitor ing locations, national impr ov ements ha v e slowed. One-hour ozone le v els for 2001 ar e 11 per cent lower than those for 1982 b ut less than 1 per cent below 1992 le v els. In 2001, for the sixth consecuti

v e year , r ural 1-hour ozone le v els, on a v erage , a r e gr eater than the le v els obser v ed for the urban sites, b ut the y ar e still generally lower than le v els obser v ed at sub urban sites. Ov er the past 10 year s, the a v erage 8-hour ozone le v el in 33 of our national parks incr eased almost 4 per cent. Six monitor ing sites in fi v e of these parks exper ienced statistically significant upward tr ends in 8-hour ozone le v els: Gr eat Smoky Mountains (T ennessee), Crater s of the Moon (Idaho), Mesa V e rde (Colorado), Mammoth Ca v e (K entucky), and Y ellowstone (W yoming). Monitoring data for tw o parks sho wed statistically significant impr ov ements ov er the same time per iod: Saguar o (Ar izona) and Sequoia (Califor nia). F o r the r emaining 26 parks wher e ozone monitor ing tak es place , t he 8-hour ozone le v els at 18 incr eased only slightly between 1992 and 2001, while 5 showed decr easing le v els and 3 we r e unchanged. **1982–01: 18%**  **decrease 1992–01:**  **3% decrease** **9**Six Principal Pollutants 

### T

**rend in 1-Hour Ozone Le vels,**  **1982–2001, A**  **vera g**  **ed acr oss EP**  **A Regions** Based on Annual 2nd Highest Daily Maximum


## 10

**9 8**  **7**

**6 5** 

**4 3**  **2 1**  .156 .1 19

**24% 17%** 

.126
**10%**

**7%** .105 .098

**The National T**  **rend 14%**  .1 15 .099

**6%** .093 .099

**16%** .108 .128 **15%** .098 .1 15 **29%** . 111

**32%** .154

**18%** .104

.127 .133

. 111 1982 2001 1982 2001

1982 2001

1982 2001

1982 2001 1982 2001

1982 2001 1982 2001

1982 2001

1982 2001 1982 2001 .079

.104 .1 13

Rur al Sub urban Urban 0.00 0.02 0.04 0.06 0.08 0.10 0.12 0.14 0.16

82 83 84 85 86 88 89 90 91 92 93 94 95 96 97 98 99 00 01 87Concentration, ppm **NAA QS**  **T**

**rend in 1-hour Ozone Le vels,**  **1982–2001, b**  **y Location of Site**  Based on Ann ual 2nd Highest Daily Maxim um

Concentr ations are in par ts per million (ppm). 

### T

**rend in 8-Hour Ozone Le vels,**  **1982–2001, A**  **vera g**  **ed acr oss EP**  **A Regions** Based on Ann ual 4th Maxim um 8-Hour A v er age 

## 10

**9 8**  **7**

**6 5** 

**4 3**  **2 1** 
**20% 8%** 

**4%**

**2%**

**The National T**  **rend 9%** 

**0%**

**9% 9%**  **21%**

**24%** 1982 2001 .090 .112

1982 2001 .093 .101

1982 2001 .092 .096 1982 2001 .081 .089

1982 2001 .080 .082

1982 2001 .082 .090 1982 2001 .074 .074 1982 2001 .074 .081

1982 2001 .078 .102 1982 2001 .057 .072

1982 2001 .082 .092
**11%** *EP A Regional Office contacts can be found at www .epa.gov/epahome/locate2.htm. ***10**Six Principal PollutantsThousand ShortTonsConcentration, ppm **SULFUR DIOXIDE (SO 2**  **)**

**Natur e and Sour**  **ces of the Pollutant** Sulfur dioxide belongs to the f a mily of SO x gases. These gases ar e for med when fuel containing sulfur (mainly coal and oil) is b u r n ed and dur ing metal smelting and other industr ial pr ocesses. Most SO 2 monitor ing stations ar e located in urban ar eas. The highest monitor ed concentrations of SO 2 ar e r ecorded in the vicinity of large industr ial f acilities. Fuel comb ustion, largely fr om coal-fir ed power plants, accounts for most of the total SO 2 emissions. **SO 2**  **Air Quality ,**  **1982–2001** Based on Ann ual Ar ithmetic A v er age
0.04

0.03

0.02

0.01

0.00 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 00 01 **NAA QS**  253 Sites

10% of sites ha v e concentr ations belo w this line 90% of sites ha v e concentr ations belo w this line
Av e r age

**1982–01: 52%**  **decrease 1992–01:**  **35% decrease**  Air quality concentr ations do not alw ays tr ac k nationwide emissions

. For a detailed explanation, see page 3.
**SO 2**  **Emissions, 1982–2001** 
Fuel Comb ustion Industr ial Processes Tr anspor tation 30,000
25,000
20,000
15,000
10,000
5,000

0 82 85 92 93 94 95 96 97 98 99 00 01 In 1985, EP A refined its methods f or estimating emissions

. **Health and Envir onmental Ef**  **fects** High concentrations of SO 2 can r esult in temporar y br eathing impair ment for asthmatic childr en and adults who ar e acti v e outdoor s. Shor t-ter m exposur es of asthmatic indi viduals to ele vated SO 2 le v els dur ing moderate acti vity ma y r esult in br eathing difficulties that can be accompanied by symptoms such as wheezing, chest tightness, or shor tness of br eath. Other effects that ha v e been associated with longer-ter m exposur es to high concentrations of SO 2 , in conjunction with high le v els of PM, include agg ra vation of existing car diovascular disease , r espirator y illness, and alterations in the lungs’ defenses. The subg r oups of the population that ma y be affected under these conditions include indi viduals with hear t or lung disease , as well as the elderly and childr en. To gether , S O 2 and NO x ar e the major pr ecur sor s to acidic deposition (acid rain), which is associated with the acidification of soils, lak es, and str eams and accelerated cor r osion of b uildings and mon uments. SO 2 also is a major pr ecur sor to PM 2.5 , which is a significant health concer n as well as a main contr ib utor to poor visibility

. (See Acid Rain section, page 16, for a mor e detailed discussion.) **Tr ends in SO**  **2 Levels and Emissions**  Nationally , a

v erage SO 2 ambient concentrations ha

v e decr eased 52 per cent fr om 1982 to 2001 and 35 per cent ov er the mor e r ecent 10-year per iod 1992 to 2001. SO 2 emissions decr eased 25 per cent fr

om 1982 to 2001 and 24 per cent fr om 1992 to 2001. Reductions in SO 2 concentrations and emissions since 1990 ar e due , in large par t, to contr ols implemented under EP A’

s Acid Rain Pr

o g ram beg inning in 1995.

**1982–01: 25%**  **decrease 1992–01:**  **24% decrease** **11**Six Principal Pollutants **Natur e and Sour**  **ces of the Pollutant** Pa r ticulate matter is the general ter m used for a mixtur e of solid par ticles and liquid dr oplets found in the air

. Some par ticles ar e large enough to be seen as dust or dir t. Other s ar e so small the y can be detected only with an electr on micr oscope
. P M 2.5 descr ibes the “fine” par ticles that ar e less than or equal to 2.5 μm in diameter

. “Coar se fraction” particles ar e g r eater than 2.5 μm, b ut less than or equal to 10 μm in diameter

. P M 10 r efer s to all par ticles less than or equal to 10 μm in diameter

. A par ticle 10 μm in diameter is about one-se v enth the diameter of a human hair

. PM can be emitted dir ectly **PA R**  **TICULA TE MA**  **TTER**

or for m in the atmospher e . “Pr imar y” par ticles, such as dust fr om r oads or elemental carbon (soot) fr

om w ood comb ustion, ar e emitted dir ectly into the atmospher e . “Secondar y” par ticles ar e for med in the atmospher e fr om pr imar y gaseous emissions. Examples include sulf ates, for med fr om SO 2 emissions fr om power plants and industr ial f a cilities, and nitrates, for med fr om NO x emissions fr om powe r plants, automobiles, and other types of comb ustion sour ces. The chemical composition of par ticles depends on location, time of year , and we ather

. Generally , coar se PM is composed largely of pr imar y par ticles and fine PM contains man y mor e secondar y par ticles. **Health and Envir onmental Ef**  **fects** Pa r ticles that ar e small enough to get into thelungs (those less than or equal to 10 μm in diameter) can cause n umer ous health pr ob lems and ha

v e been link ed with illnesses and deaths fr om hear t and lung diseases. V a r ious health pr ob lems ha

v e been associated with long-ter m (e .g., multiyear) exposur es as well as daily and e v en, potentially , peak (e .g., 1-hour) exposur es to par ticles. Pa r ticles can agg ra vate r espirator y conditions such as asthma and br onchitis and ha v e been associated with cardiac ar rh ythmias (hear tbeat ir r egular ities) and hear t attacks. P a r ticles of concer n can include both fine and coar se-fraction par ticles, although fine par ticles ha v e been mor e clearly link ed to the most ser ious health effects. P eople with hear t or lung disease , the elderly , and childr en ar e at highest
r isk fr om exposur e to par ticles. In addition to health pr ob lems, PM is the major cause of r educed visibility in man y par ts of the United States. Airbor ne par ticles also can impact v egetation and ecosystems and can cause damage to paints and b uilding mater ials. (See Acid Rain, NO 2 , and SO 2 sections.) **Tr ends in PM**  **10 Levels and Dir**  **ect Emissions** Between 1992 and 2001, a v erage PM 10 concentrations decr eased 14 per cent, while dir ect PM 10 emissions decr eased 13 per cent. 0 10 20 30 40 50 60

92 93 94 95 96 97 98 99 00 01Concentration,μg/m3 **NAA QS** 

10% of sites ha v e concentr ations belo w this line 90% of sites ha v e concentr ations belo w this line
Av e r age **PM 10**  **Air Quality ,**  **1992–2001** Based on Seasonally W eighted Ann ual A v er age
770 Sites

**1992–01: 14% decrease** 

82 85 92 93 94 95 96 97 98 99 00 01 0 1,000 2,000 3,000 4,000 5,000 7,000Thousand ShortTons **PM 10**  **Emissions, 1982–2001** 

6,000 In 1985, EP A refined its methods f or estimating emissions

. Fuel Comb ustion Tr anspor tation Industr ial Processes

**1992–01: 13%**  **decrease** Emission trends data not av

ailab le

. Air quality concentr ations do not alw ays tr ac k nationwide emissions

. For a detailed explanation, see page 3.**12**Six Principal Pollutants

15 μ g/m 3 20 μ g/m 3 10 μ g/m 3 Sulf ate Ammonium Nitr ate T otal Carbon Cr ustal Mater ial

**Ann ual A**  **vera g**  **e PM**  **2.5 Concentrations (μ**  **g/m 3**  **) and P**  **a r**  **tic le**  **T ype in Rural Areas,1999** 

Source: Inter agency Monitor ing of Protected Visual Environments Network, 1999. **Tr ends in PM**  **2.5 Levels and Dir**  **ect Emissions** The char t at r ight shows that dir ect PM 2.5 emissions fr om man-made sour ces decr eased 10 per cent nationally between 1992 and 2001. This char t tracks only dir ectly emitted par ticles and does not account for secondar y par ticles for med when emissions of NO x , S O 2 , ammonia, and other gases r eact in the atmospher e . The pr incipal types of secondar y par ticles ar e sulf ates and nitrates, which ar e for med when SO 2 and NO x r eact with ammonia. The maps at r ight show how sulf ates and nitrates, along with other components, contr ib ute to PM 2.5 concentrations. The fir st map r epr esents the most r ecent year of data a vailab le fr om the Interagency Monitor ing of Pr otected Visual En vir onments (IMPR O

VE) netw ork, which was estab lished in 1987 to track tr ends in pollutants, such as PM 2.5 , that contr ib ute to visibility impair ment. Because the monitor ing sites ar e located in r ural ar eas thr oughout the countr y , the netw ork is a good sour ce for assessing r e g ional differ ences in PM 2.5 . The second map r epr esents the most r ecent year of data fr om EP A’

s urban speciation netw ork, which was estab lished in 1999. All of these sites ar e located in urban ar eas. Sites in the r ural East typically ha v e higher ann ual av erage PM 2.5 concentrations than those in the r ural W est, as shown b y the larger cir cles in the East. Most of this r e g ional differ ence is attr ib utab le to higher sulf ate concentrations in the easter n United States. Sulf ate concentrations in the East largely r esult fr om SO 2 emissions fr om coal-fir ed power plants. Sites in urban ar eas, as shown in the cir cles in the map at r ight, generally ha v e higher ann ual a v erage PM 2.5 concentrations than nearb y r ural ar eas. Carbon fr om soot and organic compounds accounts for much of the differ ence , while sulf ate concentrations ar e about the same

. Sites in central Califor nia show that nitrates, in addition to carbon, ar e r esponsib le for higher urban concentrations in that r e g i on. Tr ends in r ural PM 2.5 concentrations can be examined with data fr om the IMPR O

VE netw ork. A t the time of this r epor t, 2000 and 2001 data we r e not a vailab le

. H owe v e r , 36 sites ha v e enough data to assess tr ends fr om 1992 to 1999. In the East, wher e sulf ates contr ib ute most to r ural PM 2.5 , the Sulf ate Ammonium Nitr ate T otal Carbon Cr ustal Mater ial 15 μ g/m 3 20 μ g/m 3 10 μ g/m 3 **Ann ual A**  **vera g**  **e PM**  **2.5 Concentrations (μ**  **g/m 3**  **) and P**  **a r**  **tic le**  **T ype in Urban Areas,**  **2001**

Source: EP A Speciation Network, 2001. 0 500 1,000 1,500 2,000 2,500Thousand ShortTons **Direct PM 2.5**  **Emissions, 1992–2001** 

92 93 94 95 96 97 98 99 00 01 **1992–01: 10%**  **decrease** Fuel Comb ustion Tr anspor tation Industr ial Processes

Note: Direct compar isons of the infor mation in these two maps should take into consider ation: the f act that they represent different y ears; that one is an urban network and the other is a rur al network; and that there are also differences in instruments and measurement methods

. If enacted, President Bush's Clear Skies Initiative would decrease PM concentrations by dramatically reducing emissions of SO 2 and NO x . This initiative would also reduce mercury emissions (www .epa.gov/clearskies).**13**Six Principal Pollutants ann ual a v

erage acr oss the 10 sites decr eased 5 percent fr om 1992 to 1999. The peak in 1998 is associated with incr eases in sulf ates and carbon fr om soot and organic compounds. A v

erage PM 2.5 concentrations acr oss the 26 sites in the W est w ere less than one-half of the le v els measur ed at easter n sites fr

om 1992 to 1999. In 1999, EP A and its state , tr ibal, and local air pollution contr ol par tner s deplo yed a monitor ing netw ork to beg in measur ing PM 2.5 concentrations nationwide

. The map at left shows ann ual a v erage PM 2.5 concentrations b y county
. This map also indicates that PM 2.5 concentrations var y r eg ionally

. Based on the monitor ing data, par ts of Califor nia and much of the easter n United States ha v e ann ual av erage PM 2.5 concentrations abov e the le v el of the ann ual PM 2.5 standard, as indicated b y the orange and r ed on the map

. With fe w exceptions, the r est of the countr y generally has ann ual a v erage concentrations below the le v el of the ann ual PM 2.5 health standar d. No w that ther e ar e 3 y ear s of monitor ing data availab le , we ha v e begun to examine tr ends at the national le v el. Ann ual a v erage PM 2.5 concentrations decr eased 5 per cent nationally fr om 1999 to 2001, with much of that decr ease occur r ing between 2000 and 2001. This decr ease ma y or ma y not r epr esent a tr end, g i v en the fe w year s of data a vailab le at this time

. The Southeast was r esponsib le for most of that r eduction, wher e the monitor ed le v els of PM 2.5 decr eased 10 per cent fr om 2000 to 2001. Lower 2001 ann ual a v erage concentrations in the Southeast ar e due , in par t, to less demand on utilities dur ing a v er y war m winter

. This is illustrated by the r eduction in dir ect emissions of SO 2 and PM 2.5 fr om fuel comb ustion in 2001.

Note: The NAA QS for PM 2.5 is 15 μg/m 3 bu t is based on the av er age of 3 y ears of monitor ing data. In ad dition, PM 2.5 concentr ation measurements from the new nationwide monitor ing network are not directl y compar ab le to the measurements from the IMPRO VE network due to differences in instruments and measurement methods

. Concentr ation ( μ g/m 3 )

> 20 15 - 20 12 - 15 < 12 Do not meet minim um data completeness Source: U.S. EP A AIRS databases as of 7/8/02. Minim um 11 samples per calendar quar ter required.

0 5 10 15 20 25 30 486 Sites

**NAA QS**  **PM 2.5**  **Air Quality ,**  **1999–2001** Based on Seasonally W eighted Ann ual A v er age

**1999–01: 5%**  **decrease**Concentration,μg/m3

00 01 99 97 98 96 95 93 94 92 Av e r age 90% of sites ha v e concentr ations belo w this line

10% of sites ha v e concentr ations belo w this line T rends monitor ing data f or PM

2.5

not available. Source: Interagency Monitoring of Protected Visual Environments Network, 1999.
**Annual Average PM 2.5**  **Concentrations (μg/m 3**  **), 2001** 14
12
10
8
6
4
2
0 **Ann ual A**  **vera g**  **e PM 2.5**  **Concentrations in Rural Areas** 

Sulf ate (Easter n U .S .–10 sites) Measured PM 2.5 (W ester n U .S .–26 sites)

Measured PM 2.5 (Easter n U .S .–10 sites)

Carbon (Easter n U .S .–10 sites)

99 98 97 96 95 94 93 92Concentration,μg/m3**CARBON MONOXIDE (CO)**

**14**Six Principal PollutantsConcentration, ppm **Natur e and Sour**  **ces of the Pollutant** Carbon monoxide is a colorless and odorless gas, for med when carbon in fuel is not b u r ned completely

. It is a component of motor v ehicle exhaust, which contr ib utes about 60 per cent of all CO emissions nationwide

. Nonr oad v ehicles account for the r emaining CO emissions fr om transpor tation sour ces. High concentrations of CO generally occur in ar eas with hea vy traffic congestion. In cities, as much as 95 per cent of all CO emissions ma y come fr om automobile exhaust. Other sour ces of CO emissions include industr ial pr ocesses,

Air quality concentr ations do not alw ays tr ac k nationwide emissions

. For a detailed explanation, see page 3.

82 85 92 93 94 95 96 97 98 99 00 01 0 20,000 40,000 60,000 80,000 100,000 140,000Thousand ShortTons **CO Emissions, 1982–2001** 

120,000 In 1985, EP A refined its methods f or estimating emissions

. Fuel Comb ustion Tr anspor tation Industr ial Processes Miscellaneous 2 4 6 8 10 12 14

0 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 00 01 **CO Air Quality ,**  **1982–2001** Based on Ann ual 2nd Maxim um 8-hour A v er age

**NAA QS**  218 Sites

10% of sites ha v e concentr ations belo w this line 90% of sites ha v e concentr ations belo w this line

Av e r age

**1982–01: 62%**  **decrease 1992–01:**  **38% decrease**  nontranspor tation fuel comb ustion, and natural sour ces such as wildfir es. P eak CO concentrations typically occur dur ing the colder months of the year when CO automoti v e emissions ar e g r eater and nighttime in v e r sion conditions (wher e air pollutants ar e trapped near the g r ound beneath a la

yer of wa r m air) ar e mor e fr equent. **Health and Envir onmental Ef**  **fects** CO enter s the b loodstr eam thr ough the lungs and r educes oxygen deli v e r y to the body’ s organs and tissues. The health thr eat fr om le v els of CO sometimes found in the ambient air is most ser ious for those who suffer fr om cardiovascular disease , such as ang ina pector is. At much higher le v els of exposur e not commonly found in ambient air , CO can be poisonous, and e v en health y indi viduals ma y be affected. Visual impair ment, r educed w ork capacity , r educed man ual dexter ity , poor lear ning ability , a nd difficulty in perfor ming complex tasks ar e all associated with exposur e to ele vated CO le v els. **Tr ends in CO Levels and Emissions**  Nationally , the 2001 ambient a v erage CO concentration is almost 62 per cent lo wer than that for 1982 and is the lo west le v el r ecor ded dur ing the past 20 y ear s. CO emissions fr om transpor tation sour ces, the major contr ib utor to ambient CO concentration, ha v e decr eased slightly dur ing this per iod. Between 1992 and 2001, ambient CO concentrations decr eased 38 per cent. This air quality impr ov ement occur r ed despite an appr o x imately 35 per cent incr ease in v ehicle miles tra v eled in the United States dur ing this 10-y ear per iod and an incr ease in total CO emissions of 6 per cent. The r ecent incr ease in CO emissions was caused by an extr emely ser ious wildfir e season in 2000. Nearly twice the n umber of U

. S

. acr es b u r ned in 2000 compar ed to the a v erage year since 1982.

**1982–01: 0%**  **c hang**  **e 1992–01:**  **6% increase 15** Six Principal Pollutants **LEAD (Pb)**

**Natur e and Sour**  **ces of the Pollutant** In the past, automoti v e sour ces we r e the major contr ib utor of lead emissions to the atmospher e . As a r esult of EP A’

s r egulator y effor ts to r educe the content of lead in gasoline , h owe v e r , the contr ib ution of air emissions of lead fr om the transpor tation sector , and par ticularly the automoti v e sector , has gr eatly declined ov er the past tw o decades. T oda y

, industr ial pr ocesses, pr imar ily metals pr ocessing, ar e the major sour ce of lead emissions to the atmospher e . The highest air concentrations of lead ar e usually found in the vicinity of smelter s and batter y man uf actur er s. **Health and Envir onmental Ef**  **fects** Exposur e to lead occur s mainly thr ough inhalation of air and ingestion of lead in food, water , soil, or dust. It accumulates in the b l ood, bones, and soft tissues and can adv er sely affect the kidne ys, li v e r , ner vous system, and other organs. Excessi v e exposur e to lead ma y cause neur olo g ical impair ments such as seizur es, mental r etar dation, and beha vioral disorder s. Ev en at lo w doses, lead exposur e is associated with damage to the ner vous systems of fetuses and young childr en, r esulting in lear ning deficits and lowe r ed IQ

. Recent studies also show that lead ma y be a f actor in high b lood pr essur e and subsequent hear t disease

. Lead can also be deposited on the lea v es of plants, pr esenting a hazard to g razing animals and humans thr ough ingestion. **Tr ends in Lead Levels and Emissions**  Because of the phaseout of leaded gasoline , lead emissions and concentrations decr eased shar ply dur ing the 1980s and early 1990s. The 2001 av erage air quality concentration for lead is 94 per cent lower than in 1982. Emissions of lead decr eased 93 per cent ov er that same 20-year per iod. T oda y

, the only violations of the lead NAA QS occur near large industr ial sour ces such as lead smelter s and batter y man uf actur er s. V a r i ous enfor cement and r egulator y actions ar e being acti v ely pur sued b y EP A and the states for cleaning up these sour ces. Air quality concentr ations do not alw ays tr ac k nationwide emissions

. For a detailed explanation, see page 3. 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 00 01 0.0 **Lead Air Quality ,**  **1982–2001** Based on Ann ual Maxim um Quar ter ly A v er ag e

**NAA QS** 

1.0 1.5 2.0

0.5Concentration,μg/m3 39 Sites

10% of sites ha v e concentr ations belo w this line 90% of sites ha v e concentr ations belo w this line

Av e r age

**1982–01: 94%**  **decrease 1992–01:**  **25% decrease** 

85 92 93 94 95 96 97 98 99 00 01 82 0Short Tons **Lead Emissions, 1982–2001** 

In 1985, EP A refined its methods f or estimating emissions

.

**1982–01: 93%**  **decrease** 20,000 40,000 60,000 80,000 Fuel Comb ustion Tr anspor tation Industr ial Processes**16** 

# Acid Rain

**Natur e and Sour**  **ces of the Pr oblem**  Acidic deposition or “acid rain” occur s when emissions of sulfur dioxide and nitr o gen oxides in the atmospher e r eact with water , o xygen, and oxidants to for m acidic compounds. These

**Acid Rain SO**  **2 NO**  **x Acid Rain Formation** 

Coal-fired electr ic utilities and other sources that b u r n fossil fuels emit S O 2 and N O x . **SO 2**  **Emissions Co vered under**  **the Acid Rain Pr ogram**  20 18 16 14 12 10 8 6 4 2 2000 1999 1998 1997 1996 1995 1990 1985 1980

Phase II units not aff ected f or NO x Phase II NO x aff ected units (1,046) Projected NO x emissions without the Acid Rain Prog r a m 2000 1999 1998 1997 1996 1995 1990 4.48 4.82 5.29 5.49 5.44 5.54 5.53 5.11 5.49 5.97 6.04 5.91 6.09 6.66 8.1 6.7 **NO x**  **Emissions Co vered under**  **the Acid Rain Pr ogram**  compounds f all to the Ear th in either dr y for m (gas and par ticles) or wet for m (rain, snow , and fo g). Some ar e car r ied b y the wind, sometimes hundr eds of miles, acr oss state and national border s. In the United States, about 64 per cent of ann ual SO 2 emissions and 26 per cent of NO x emissions ar e pr oduced b y electr ic utility plants that b u r n fossil fuels. **Health and Envir onmental Ef**  **fects** In the en vir onment, acid deposition causes soils and waterbodies to acidify (making the water unsuitab le for some fish and other wildlife) and damages some tr ees, par ticularly at high ele vations. It also speeds the deca y of b uildings, statues, and sculptur es that ar e par t of our national her itage

. The nitr o gen por tion of acid deposition contr ib utes to eutr ophication in coastal ecosystems, the symptoms of which include algal b looms (some of which ma y be toxic), fish kills, and loss of plant and animal di v e r sity

. Finally , acidification of lak es and str eams can incr ease the amount of meth yl mer cur y a vailab le in aquatic systems. Most exposur e to mer cur y comes fr om eating contaminated fish. Reductions in SO 2 and NO x ha v e begun to r educe some of these negati v e en vir onmental effects and ar e leading to significant impr ov ements in pub lic health (descr ibed pr e viously). **Pr ogram Structur**  **e** The goal of EP A’

s Acid Rain Pr o g ram, estab lished by the Clean Air Act, is to impr ov e pub lic health and the en vir onment b y r educing emissions of SO 2 and NO x . The pr o g ram was implemented in tw o phases: Phase I for SO 2 began in 1995 and targeted the largest and highest-emitting coal-fir ed po we r plants. Phase I for NO x began in 1996. Phase II for both pollutants began in 2000 and sets r estr ictions on Phase I plants as well as smaller coal-, gas-, and oil-fir ed plants. Ov er 2,000 sour ces ar e now affected b y the Acid Rain Pr o g ram. The Acid Rain Pr o g ram will r educe ann ual SO 2 emissions b y 10 million tons fr om 1980 le v els by 2010. The pr o g ram sets a per manent cap of 8.95 million tons on the total amount of SO 2 that ma y be emitted b y po wer plants nationwide , about half the amount emitted in 1980. It emplo ys an emissions trading pr o g ram to r each that emissions cap mor e efficiently and cost-effecti v ely

. Sour ces ar e allocated allo wances efficiently each y ear (one allo wa nce equals 1 ton of SO 2 emissions), which can be bought or sold or bank ed for futur e use .Million TonsNOxMillion TonsSO2

0

9 8 7 6 5 4 3 2 1 0This appr oach g i v es sour ces the flexibility and incenti v e to r educe emissions at the lowest cost while ensur ing that the emission cap is met. The NO x component of the Acid Rain Pr o g ram limits the emission rate for all affected utilities, r esulting in a 2 million ton NO x r eduction fr om 1980 le v els b y 2000. Ther e is no cap on total NO x emissions, b ut under this pr o g ram a sour ce can choose to ov er-contr ol at units wher e it is technically easier to contr ol emissions, a v erage these emissions with those at their other units, and ther eb y achie v e ov erall emissions r eductions at lo wer cost. **Emissions and Atmospheric T r**  **ends** SO 2 emissions r eductions ha v e been significant in the fir st 6 y ear s of EP A’

s Acid Rain Pr o g ram. The fir st year of compliance with Phase II of the Acid Rain Pr o g ram was 2000. Sour ces in the Acid Rain Pr

o g ram emitted 11.2 million tons in 2000, down fr

om 16 million tons in 1990. Emissions of SO 2 dr

opped 1 million tons between 1999 and 2000. Sour ces began dra wing do wn the bank of un used allowances in 2000, r esulting in emissions le v els gr eater than the allo wances allocated in 2000 b u t still lo wer than emissions dur ing an y pr e vious year . Actual NO x emissions, as shown in the g raph on the bottom left of page 16, ha v e also declined since 1990. NO x emissions decr eased steadily fr om 6 tons in 1997 to just ov er 5 tons in 2000. The mor e than 1,000 sour ces affected b y Phase II emitted 4.5 tons in 2000, ov er 1 million tons (almost 20 per cent) less than the y did in 1990. NO x emissions in 2000 we r e some what lower (7 per cent) than in 1999 and almost half of what emissions we r e pr ojected to ha v e been in 2000 without the Acid Rain Pr o g ram. F or all year s fr om 1995 thr ough 2000, sulf ate deposition exhibited dramatic and unpr ecedented r eductions ov er a large ar ea of the easter n United States. A v erage sulf ate deposition in 1996–2000 compar ed to 1990-1994 was 10 per cent lowe r nationwide and 15 per cent lower in the East. Similarly , sulf ate air concentrations, which contr ib ute to human health and visibility pr ob lems, we re r educed significantly , especially in the East. Nitrate deposition decr eased slightly in some places b ut incr eased in other s, causing an ov erall a v erage incr ease in nitrate deposition between 1990–1994 and 1996–2000 of 3 per cent. These r eductions in acid pr ecipitation ar e dir ectly r elated to the large r e g ional decr eases in SO 2 and NO x emissions r esulting fr om the Acid Rain Pr

o g ram. The largest r eductions in sulfate concentrations occur r ed along the Ohio Ri v er V alle y and in states immediately downwind. The largest r eductions in wet sulf ate deposition occur r ed acr oss the Mid-Appalachian and Nor theast r e g ions of the countr y . Reductions in the East in h ydr o gen ion concentrations, the pr imar y indicator of pr ecipitation acidity , wer e similar to those of sulf ate concentrations, both in magnitude and location. The largest r eductions in wet nitrate deposition we r e in the nor theaster n United States, Michigan, and T exas. The Midwest, the Southeast, and Califor nia showed the highest incr eases in deposition e v en though emissions fr om acid rain sour ces ha v e not incr eased substantially ther e . Acid rain sour ces account for only one-third of nationwide nitr o gen emissions, so emissions tr ends in other sour ce categor ies, especially ag r icultur e and mobile sour ces, affect air concentrations and deposition.

**17**Acid Rain **Chang e in Deposition fr**  **om Precipitation 1990–1994 to 1996–2000** 

**Sulfate**

**Nitrate**

Source: U

. S

. EP A anal ysis of National Atmospher ic Deposition Progr am data.**18** 

# Visibility

In 2000, the IMPROVE Monitoring Network, used to track visibility trends at national parks and wilderness areas, started an expansion from 30 to 110 monitoring sites. The expansion work was completed in the fall of 2001. However , due to thelevel of resources required to complete the network expansion, reporting of 2000 IMPROVE data will occur while this brochure is being finalized. Therefore, no update is provided for visibility trends reported in the 1999 Status and T rends Brochure . Reporting of 2000 and 2001 visibility trends are scheduled to be included in U.S. EP A

’ s 2001 National Air Quality and Emission T rends Report

.

**Natur e and Sour**  **ces of the Pr oblem**  Visibility impair ment is one of the most obvious effects of air pollution and occur s at man y of the best known and most tr easur ed natural parks and wilder ness ar eas, such as the Grand Can yon, Y

osemite , Y ellowstone , Mount Rainier , Shenandoah, and the Gr eat Smoky Mountain National P ark, as well as in urban ar eas. Visibility impair ment r esults fr om the scatter ing and absor ption of light b y air pollution, including par ticles and gases. The scatter ing and absor ption by air pollution limits the distance we can see and can also deg rade the color , clar ity , and contrast of scenes. The same fine par ticles that ar e link ed to ser ious health effects and pr ematur e death can also significantly affect our ability to see

. Some par ticles that contr ib ute to visibility impairment ar e emitted dir ectly into the atmospher e fr

om their sour ces, such as dust fr om r oads or elemental carbon (soot) fr om w ood comb ustion. In other cases, par ticles ar e for med in the atmospher e fr om pr imar y gaseous emissions such as SO 2 emissions fr om power plants and other industr ial f acilities and nitrates for med fr om NO x emissions fr om power plants, automobiles, and other types of comb ustion sour ces. These types of par ticles ar e r efer r ed to as secondar ily for med par ticles. In the easter n United States, r educed visibility is mainly attr ib utab le to secondar ily for med sulf ates. Although these secondar ily for med par ticles still account for a significant amount of par ticulate loading in the W est, pr imar y emissions fr om sour ces lik e w ood smok e contr ib ute a larger percentage of the total par ticulate loading than in the East. Also , humidity can significantly incr ease the effect of pollution on visibility , causing some par ticles to become mor e efficient at scatter ing light and causing visibility impair ment. Ann ual a v erage r elati v e humidity le v els ar e 70 to 80 per cent in the East as compar ed to 50 to 60 per cent in the W est. P oor summer visibility in the easter n United States is pr imar ily the r esult of high sulfate concentrations combined with high humidity le v els. **East W**  **est** Sulf ates 60–86% 25–50% Organic Carbon 10–18% 25–40% Nitrates 7–16% 5–45% Elemental Carbon (soot) 5–8% 5–15% Cr ustal Mater ial (soil dust) 5–15% 5–25% This tab le shows pollutants that contr ib ute to visibility impair ment in the easter n and wester n par ts of the United States

. Sulf ates are gener all

y the largest contr ib utor in both the East and the W est. **Pr ogram Structur**  **e** The Clean Air Act pr ovides for the pr otection of visibility in national parks and wilder ness ar eas, also known as Class I ar eas. The Clean Air Act’ s national goal calls for r emedying existing visibility impair ment and pr e v enting futur e impair ment in these 156 Class I ar eas acr oss the countr y . **Class I Areas**



### The Clean Air Act provides for the protection of visibility in our national parks and wilder ness areas , also known as Class I areas

. There are 156 Class I areas across the United States as shown.
In 1987, the IMPR O

VE visibility netw ork wa s estab lished as a cooperati v e effor t among EP A, states, National P ark Ser vice , U.S

. F or est Ser vice , Bur eau of Land Management, and U

. S

. Fish and Wildlife Ser vice

. Data ar e collected and analyzed fr

om this netw ork to deter mine the type of pollutants pr imar ily r esponsib le for r educed visibilityand to track pr o g r ess towa rd the Clean Air Act’ s national goal. In Apr il 1999, EP A initiated a ne w r e g ional haze pr

o g ram. The pr o g ram addr esses visibility impairment in national parks and wilder ness ar eas caused by n umer ous sour ces located ov er br oad r e g ions. The pr o g ram sets a frame w ork for states to de v elop goals for impr oving visibility on the w o r st visibility da

ys each year and to adopt emission strateg ies to meet these goals. Because fine par ticles ar e fr equently transpor ted hundr eds of miles, pollution that occur s in one state ma y contr ib ute to the visibility impair ment in another state

. F or this r eason, EP A encourages states to coordinate thr ough r e g ional planning organizations to de v elop re g ional strateg ies to impr ov e visibility and to r educe pollutants that contr i b ute to fine par ticles and g r ound-le v el ozone

. States ar e also r equir ed to r e vie w pr o g r ess e v er y 5 year s and r e vise an y strateg ies as necessar y . **V isibility T**  **r ends**  Without the effects of pollution, a natural visual range in the United States is appr o ximately 75 to 150 km (45 to 90 miles) in the East and 200 to 300 km (120 to 180 miles) in the W est. Data collected b y the IMPR O

VE netw ork show visibility impair ment for the w o r st visibility in the W est is similar to da ys with the best visibility in the East. In 1999, mean visual range for the

**19**Visibility Shenandoah National P ark under bad and good visibility conditions

. The visual r ange in the top photo is 25 km while the visual r ange in the bottom photo is 180 km. Y osemite National P ark under bad and good visibility conditions

. The visual r ange in the top photo is 111 km while the visual r ange in the bottom photo is greater than 208 km.

50 100 150 200 250

0
**Y ear**  **Visibility T**  **rends f or Eastern**  **U .S.**  **Class I Areas, 1992–1999** Visual Range (km)

92 93 94 95 96 97 98 99 Best visibility r ange is 79-90 km Mid-r ange visibility is 42-48 km W orst visibility r ange is 20-23 km

W orst Visibility Mid-Range Best Visibility

Visibility Metr ics . C ompar isons of extinction (Mm -1 ), deciviews (dv), and visual r a nge (km). Notice the difference in the three scales: 10 Mm -1 cor responds to about 400 km visual r ange and 0.0 dv , while 1,000 Mm -1 is about 4 km visual r ange and 46 dv . wo r st da ys in the East was only 24 km (14.4 miles) compar ed to 84 km (50.4 miles) for the best visibility

. In the W est, visibility impair ment for the w o r st da ys r emained r elati v ely unchanged ov er the 1990s, with the mean visual range for 1999 (80 km) nearly the same as the 1990 le v el (86 km).

50 100 150 200 250

0
**Y ear**  **Visibility T rends**  **f or**  **W estern**  **U .S.**  **Class I Areas, 1990–1999** Visual Range (km)

90 91 92 93 94 95 96 97 98 99 Best visibility r ange is 177-208 km Mid-r ange visibility is 118-133 km W orst visibility r ange is 73-85 km W orst Visibility

Mid-Range Best Visibility**20** 

# To xic Air P ollutants

**Natur e and Sour**  **ces of the Pr oblem**  Toxic air pollutants, or air toxics, ar e those pollutants that cause or ma y cause cancer or other ser ious health effects, such as r epr oducti v e effects or bir th defects. Air toxics ma y also cause adv er se en

vir onmental and ecolo g ical effects. Examples of toxic air pollutants include benzene , found in gasoline; per chlor oeth ylene , emitted fr om some dr y cleaning f acilities; and meth ylene chlor ide , used as a solv ent b y a n umber of industr ies. Most air to xics or ig inate fr om man-made sour ces, including mobile sour ces (e .g., car s, tr ucks, constr uction equipment) and stationar y sour ces (e .g., f actor ies, r efiner ies, power plants), as well as indoor sour ces (e .g., some b uilding mater ials and cleaning solv ents). Some air to xics ar e also r eleased fr om natural sour ces such as volcanic er uptions and for est fir es. The Clean Air Act identifies 188 air toxics fr om industr ial sour ces. EPA has identified 20 of these pollutants that ar e associated with mobile sour ces and one additional mobile sour ce air toxic designated “diesel par ticulate matter and diesel exhaust organic gases. ” **Health and Envir onmental Ef**  **fects** P eople exposed to toxic air pollutants at sufficient concentrations ma y exper ience va r ious health effects, including cancer , damage to the immune system, as well as neur olo g ical, r epr oducti v e (e .g., r educed fer tility), de v elopmental, r espirator y , and other health pr ob lems. In addition to exposur e fr

om br eathing air toxics, r isks also ar e associated with the deposition of toxic pollutants onto soils or surf ace water s, wher e the y ar e tak en up b y plants and ingested b y animals and e v entually magnified up thr ough the food chain. Lik e humans, animals ma y exper ience health pr ob lems due to air toxics exposur e . **Tr ends in T**  **oxic Air Pollutants** EP A and states do not maintain an extensi v e nationwide monitor ing netw ork for air toxics as the y do for man y of the other pollutants discussed in this r epor t. While EP A, states, tr ibes, and local air r egulator y agencies collect monitor ing data for a nu mber of toxic air pollutants, both the chemicals monitor ed and the geo g raphic cov e rage of the monitor s va r y fr

om state to state
. E P A

is w orking with these r egulator y par tner s to b uild upon the existing monitor ing sites to cr eate a national monitor ing netw ork for a n umber of to xic air pollutants. The goal is to ensur e that those compounds that pose the g r eatest r isk ar e measur ed. The a vailab le monitor ing data help air pollution contr ol agencies track tr ends in toxic air pollutants in va r ious locations ar ound the countr y . EP A began a pilot city monitor ing pr oject in 2001 and is scheduled to include at least 12 months of sampling in four urban ar eas and six small city/r ural ar eas (see map below). This pr o g ram is intended to help ans wer se v eral impor tant national netw ork design questions (e .g., sampling and analysis pr ecision, sour ces of va r iability , and minimal detection le v els). In addition, an initial 11-city tr ends netw ork is being estab lished that will help de v e lop national tr ends for se v eral pollutants of concer n. F or the latest infor mation on national air toxics monitor ing, see www .epa.g o v/ttn/ amtic/air txfil.html

. EP A also compiles an air toxics in v entor y as par t of the National Emissions In v entor y (NEI, for merly the National T o xics In v entor y) to estimate and track national emissions tr ends for the 188 toxic air pollutants r egulated under the Clean Air Act. In the NEI, EP A di vides emissions into four types of sector s:

San J T Detroit Cedar Rapids

San J Gr Seattle

Char

uan ampa acinto and J Pro vidence

Rio Rancho

unction leston

Map of 10 cities in monitor ing pilot project**Risk Assessment** EP A has de v eloped a National-Scale Air T oxics Assessment, which is a nationwide analysis of air to xics. It uses computer modeling of the 1996 NEI air toxics data as the basis for de v eloping health r isk estimates for 33 toxic air pollutants (a subset of the Clean Air Act’ s list of 188 air to xics plus diesel PM). The national-scale assessment is intended to pr

ovide state , local, and tr ibal agencies and other s with a better under standing of the r isks fr om inhalation exposur e to to xic air pollutants fr om outdoor sour ces. It will help EP A and states pr ior itize data and r esear ch needs to better assess r isk in the futur e and will pr ovide a baseline to help measure future tr ends in estimated health r isks. The next national-scale analysis will focus on 1999 data and will be r e leased b y the end of 2003.
**21** Tr ends for indi vidual air toxics va r y fr

om pollutant to pollutant. Benzene , which is the most widely monitor ed toxic air pollutant, is emitted fr om car s, tr ucks, oil r efiner ies, and chemical pr ocesses. The g raph below shows measur ements of benzene tak en fr om 95 urban monitor ing sites ar ound the countr y . These urban ar eas generally ha v e higher le v els of benzene than other ar eas of the countr y . Measur ements tak en at these sites sho w , on a v erage , a 47 per cent dr op in benzene le v els fr om 1994 to 2000. Dur ing this per iod, EP A phased in ne w (so-called “tier 1”) car emission standar ds; r equir ed man y cities to beg in using cleaner b u r ning gasoline; and set standar ds that r equir ed significant r eductions in benzene and other pollutants emitted fr

om oil r efiner ies and chemical pr ocesses. EP A estimates that, nationwide , benzene emissions fr om all sour ces dr opped 20 per cent fr om 1990 to 1996.Toxic AirPollutants (1) major (large industr ial) sour ces; (2) ar ea and other sour ces, which include smaller industr ial sour ces lik e small dr y cleaner s and gasoline stations, as well as natural sour ces lik e wildfir es; (3) onr oad mobile sour ces, including highwa y v ehicles; and (4) nonr oad mobile sour ces lik e aircraft, locomoti v es, and constr uction equipment. As shown in this pie char t, based on 1996 estimates, the most r ecent year of a vailab le data, the emissions of toxic air pollutants ar e r elati v ely equally di vided between the four types of sour ces. Howe v e r , this distr ib ution va r ies fr om city to city

.

**Ambient Benz ene**  **, Ann**  **ual A vera**  **g e**  **Urban Concentrations,**  **Nationwide ,**  **1994–2000**

0 1 2 3 4 5 6 7

94 95 96 97 98 99 00 10% of sites ha v e concentr ations belo w this line 90% of sites ha v e concentr ations belo w this line

Av e r age

**1994–00: 47%**  **decrease**Concentration,μg/m3 **National Air T**  **o xics Emissions,**  **1996** 4.7M T ons

Onroad

31% Area/Other 25% Major 24% Nonroad

20%

Baseline (1990–1993)Million Tons **National Air T**  **o xics Emissions**  T

otal f or 188 T o xic Air P ollutants

1996 0 1.0 2.0 3.0 4.0 5.0 6.0 7.0

33 urban air to xics 155 other air to xics

Based on the data in the NEI, estimates of nationwide air toxics emissions ha v e dr opped appr ox imately 24 per cent between baseline (1990–1993) and 1996. Thir ty-thr ee of these air toxics, which pose the g r eatest thr eat to pub lic health in urban ar eas, ha v e similarly dr opped 31 per cent. Although changes in how EP A compiled the national in v entor y ov er time ma y account for some differ ences, EP A and state r egulations, as well as voluntar y r eductions b y industr y , ha v e clearly achie v ed large r eductions in ov erall air toxic emissions.**22**Toxic AirPollutants

**Pr ograms to Reduce Air T**  **oxics** Since 1990, EP A’

s technolo gy-based emission standards for industr ial sour ces (e .g., chemical plants, oil r efiner ies, and dr y cleaner s) ha v e pr ov en extr emely successful in r educing emissions of air toxics. Once fully implemented, these standards will cut ann ual emissions of toxic air pollutants by nearly 1.5 million tons fr om 1990 le v els. EP A has also put into place impor tant contr ols for motor v ehicles and their fuels, including intr oduction of r efor mulated gasoline and low sulfur diesel fuel, and is contin uing to tak e additional steps to r educe air to xics fr om v ehicles. Fur ther mor e , air to xics emissions will fur ther decline as the motor v ehicle fleet tur ns ov er , with ne wer v ehicles r eplacing older higher emitting v ehicles. By the year 2020, these r equir ements ar e expected to r educe emissions of a n umber of air toxics (benzene , for maldeh yde , acetaldeh yde , and 1,3-b utadiene) fr om highwa y

motor v ehicles b y about 75 per cent and diesel PM b y ov er 90 percent fr om 1990 le v els. EP A has begun to look at the r isk r emaining (i.e ., the r esidual r isk) after emission r eductions for industr ial sour ces tak e effect and is also in

v estigating ne w standards for nonr oad eng ines such as constr uction equipment. In addition to national r egulator y effor ts, EP A’

s pr

o g ram includes w ork with communities on compr ehensi v e local assessments, as well as federal and r e g ional acti vities associated with pr otecting waterbodies fr om air toxics deposition (e .g., the Gr eat W ater s pr o g ram, which includes the Gr eat Lak es, Lak e Champlain, Chesapeak e Ba y

, and man y coastal estuar ies) and EP A initiati v es concer ning mer cur y and other per sistent and bioaccumulati v e toxics. F or indoor air to xics, EP A’

s pr o g ram has r elied on education and outr each to achie v e r eductions. Infor mation about indoor air acti vities is a vailab le at www .epa.g o v/iaq/

. F or mor e infor mation about EP A’

s air toxics pr

o g ram, visit the Agency’ s W eb site at www .epa.g o v/ttn/atw

. The following map shows a patter n of the distr ib ution of r elati v e cancer r isk acr oss the continental United States as estimated b y the national-scale assessment. The highest ranking 20 per cent of counties in ter ms of r isk (622 counties) contain almost thr ee-four ths of the U

. S

. population. Thr ee air toxics (chr omium, benzene , and for maldeh yde) appear to pose the g r eatest nationwide car cino genic r isk. This map does not include the potential r isk fr om diesel exhaust emissions. This is because existing health data ar e not sufficient to de v elop a n umer ical estimate of cancer r isk for this pollutant. Howe v e r , exposur e to diesel exhaust is widespr ead and EP A has concluded that diesel exhaust is a lik ely human car cino gen andranks with the other substances that the nationalscale assessment suggests pose the g r eatest r elati v e r isk. One air toxic , acr olein, is estimated to pose the highest potential nationwide for significant chr onic adv er se effects other than cancer

. F or mor e infor mation, visit www .epa.g o v/ttn/atw/nata

.

This technical assessment r epr esents an impor tant step towa rd character izing air toxics nationwide

. It is designed to help identify general patter ns in air toxics exposur e and r isk acr oss the countr y and is not r ecommended as a tool to character ize or compar e r isk at local le v els (e .g., to compar e r isks fr

om one par t of a city to another). Mor e localized assessments, including monitor ing and modeling, ar e under wa y

to help character ize local-le v el r isk. 0.0E+000 to 2.2E-005 2.2E-005 to 2.5E-005 2.5E-005 to 2.8E-005 2.8E-005 to 3.5E-005 3.5E-005 to 1.9E-005 **Median County Risk County Risk Comparison**  Estimated b y National-Scale Assessment

Highest

Lo w est**23** 

# Stratospher ic Ozone

thr ough the lo wer par t of the atmospher e , called the tr opospher e , and into the stratospher e . Ther e , str

ong solar radiation r eleases chlor ine and br omine atoms that attack pr otecti v e ozone molecules. Scientists estimate that one chlor ine atom can destr o

y

100,000 ozone molecules. **Health and Envir onmental Ef**  **fects** Some UV -b radiation r eaches the Ear th’ s surf ace ev en with nor mal ozone le v els. Howe v e r , because the ozone la yer nor mally absorbs most UV -b radiation fr om the sun, ozone depletion is expected to lead to incr eases in har mful effects associated with UV -b radiation. In humans, UV -b radiation is link ed to skin cancer , including melanoma, the for m of skin cancer with the highest f a tality rate

. It also causes cataracts and suppr ession of the immune system. The effects of UV -b radiation on plant and aquatic ecosystems ar e not we ll under stood. Howe v e r , the gr

o wth of cer tain food plants can be slowe d b y excessi v e UV -b radiation. In addition, some scientists suggest that mar ine ph ytoplankton, which ar e the base of the ocean food chain, ar e alr eady under str ess fr om UV -b radiation. This str ess could ha v e adv er se consequences for human food supplies f r om the oceans.

**Pr ograms to Restor**  **e the Stratospheric Ozone Layer**  In 1987, 27 countr ies, including the United States, signed the Montr eal Pr otocol, a tr eaty that r eco gnized the inter national natur e of ozone depletion and committed the w orld to limiting the production of ozone-depleting substances. T oda y

, mor e than 180 nations ha v e signed the Pr otocol, which has been str engthened fi v e times and now calls for the elimination of those chemicals that deplete stratospher ic ozone

. The 1990 Clean Air Act Amendments estab lished a U

. S

. r egulator y pr o g ram to protect the stratospher ic ozone la ye r . In J a n uar y 1996, U

. S

. production of man y

ozone-depleting substances vir tually ended, including CFCs, carbon tetrachlor ide , and meth yl chlor ofor m. Pr oduction of halons ended in J a n uar y 1994. Man y ne w pr oducts that either Monthl y av er age total oz one measured in Dobson units (DU) at four mid-latitude stations across the United States from 1979 to 1997. The trend line shows a 3.4 percent decrease in av er age total oz one ov er mid-latitudes in the United States since 1979. The large annual va r iation shown in eac h of the four cities is a result of oz one tr anspor t processes that cause increased lev els in the winter and spr ing and lower oz one lev els in the summer and f all at these latitudes

. **Natur e and Sour**  **ces of the Pr oblem**  The stratospher e , located about 6 to 30 miles abov e the Ear th, contains a la yer of ozone gas that pr

otects li ving organisms fr om har mful ultra violet radiation (UV -b) fr om the sun. Ov er the past thr ee decades, howe v e r , it has become clear that this pr

otecti v e shield has been damaged. Each year , a n “ozone hole” for ms ov er the Antar ctic , and ozone le v els ther e can f all to 60 per cent below nor mal. Ev en ov er the United States, ozone le v els ar e about 3 per cent below nor mal in the summer and 5 per cent below nor mal in the winter

. As the ozone la y er thins, mor e UV -b radiation r eaches the Ear th. The 1998 Scientific Assessment of Stratospher ic Ozone fir mly estab lished the link between decr eased ozone and incr eased UV -b radiation. In the 1970s, scientists had link ed se v eral substances associated with human acti vities to ozone depletion, including the use of chlorofluor ocarbons (CFCs), halons, carbon tetrachlor ide , meth yl br omide , and meth yl chlor ofor m. These chemicals ar e emitted fr om commer cial air conditioner s, r efr igerator s, insulating foam, and some industr ial pr ocesses. Str ong winds car r y them

96 92 88 90 86 84 80 82 78Total Ozone (DU)

275 300 325 350 375 400

225 98 94 **T rend:**  **3.4% decrease** 

Y ear Boulder ,

CO W allops Is

. F resno , CA Nashville , TN

Source: National Oceanic and Atmospher ic Administr ation (NO AA), 1998.**24**Stratospheric Ozone

do not affect or are less damaging to the ozone layer are now gaining popularity. For example, computer makers are using ozone-safe solvents to clean circuit boards, and automobile manufacturers are using HFC-134a, an ozone-safe refrigerant, in new motor vehicle air conditioners. In some industries, the transition away from ozone-depleting substances has already been completed. EPA is also emphasizing new efforts like the UV Index, a daily forecast of the strength of UV radiation to which people may be exposed outdoors, to educate the public about the health risks of overexposure to UV radiation and the steps they can take to reduce those risks. **Tr ends in Stratospheric Ozone Depletion**  Scientific evidence shows that the approach taken under the Montreal Protocol has been effective to date. Measurements have shown that atmospheric concentrations of methyl chloroform are falling, indicating that emissions have been greatly r educed. Concentrations of other ozone-depleting substances in the upper layers of the atmosphere, like CFCs, are also beginning to decrease. It takes several years for these substances to reach the stratosphere and release chlorine and bromine. F or this reason, stratospheric chlorine levels are currently peaking and are expected to slowly decline in the years to come. Because of the stability of most ozone-depleting substances, chlorine will be released into the stratosphere for many years, and the ozone layer will not fully r ecover until the second half of this century.All nations that signed the Protocol must complete implementation of ozone protection programs if full repair of the ozone layer is to happen. A 1996 study using satellite-based analyses of UV-b trends demonstrated that UV-b level had increased at ground level. This figure shows the percent increases in average annual UV-b reaching the surface from 1986 to 1996. UV-b incidence is strongly dependent on latitude.At latitudes that cover the United States, UV-b levels are 4 to 5 percent higher than they were in 1986. **UV-b Radiation Increases by Latitude**

65N: 6.8% 55N: 7.3% 45N: 5.0% 35N: 3.9% 25N: 1.2% 15N: 0.1%

Equator 15S: 2.3% 25S: 2.6% 35S: 2.9% 45S: 5.5% 55S: 9.9% 65S: 11.0% DC Edmonton

Buenos Aires Johannesburg London Moscow

Melbourne**25** 

# Conclusions

The Clean Air Act has resulted in many improvements in the quality of the air in the United States. Scientific and international developments continue to have an effect on the air pollution programs that are implemented by the U.S. EnvironmentalProtection Agency and state, local, and tribal agencies. New data help identify sources of pollutants and the properties of these pollutants.Although much progress has been made to clean up ourair, work must continue to ensure steady improvements in air quality, especially because our lifestylescreate more pollution sources. Many of the strateg ies for air quality improvement will continue to be developed through coordinated efforts with EPA, state, local and tribal governments, as well as industry and other environmental organizations.**26** 

### Acronyms CFCs chlorofluorocarbons CO 2 carbon dioxide CO carbon monoxide DU Dobson units EPA U.S. Environmental Protection Agency FCCC Framework Convention on Climate Change IMPROVE Interagency Monitoring of Protected Visual Environments IPCC Intergovernmental Panel on Climate Change km kilometers NAAQS National Ambient Air Quality Standards NAS National Academy of Sciences NCDC National Climatic Data Center NEI National Emissions Inventory NESDIS National Environmental Satellite Data and Information Service NO 2 , NO x nitrogen dioxide, nitrogen oxides NO nitric oxide NOAA National Oceanic and Atmospheric Administration O 3 ozone Pb lead PM 10 , PM 2.5 particulate matter (10 μm or less, 2.5 μm or less in diameter) ppm parts per million SO 2 , SO x sulfur dioxide, sulfur oxides VOCs volatile organic compounds UV ultraviolet**27** 

### For Further information Detailed information on Air Pollution Trends: www.epa.gov/airtrends Real-Time Air Quality Maps and Forecasts: www.epa.gov/airnow On-line Air Quality Data: www.epa.gov/air/data/index.html Office of Air and Radiation: www.epa.gov/oar Office of Air Toxics: www.epa.gov/ttn/atw Office of Air Quality Planning and Standards: www.epa.gov/oar/oaqps Office of Transportation and Air Quality: www.epa.gov/otaq Office of Atmospheric Programs: www.epa.gov/air/oap.html Office of Radiation and Indoor Air: www.epa.gov/air/oria.html Global Warming Emissions Information: www.epa.gov/globalwarming/index.html Acid Rain Web site: www.epa.gov/airmarkets/arplindex.html Acid Rain Hotline: (202) 564-9620 Energy Star (Climate Change) Hotline: (888) STAR-YES Mobile Sources National Vehicles and Fuel Emissions Lab: (734) 214-4200 Ozone Depletion Web site: www.epa.gov/ozone/**United States Environmental Protection** **Agency**Office of Air Quality and StandardsAir Quality Strategies and Standards DivisionResearch Triangle Park, NCEPA Publication No. EPA 454/K-02-001