Anne K. Rhodes
Refining/Petrochemical Editor
The U.S. Environmental Protection Agency (EPA) recently reported the air quality trends for six pollutants for which it has issued National Ambient Air Quality Standards (Naaqs).
The analyses are based on data from some 4,000 air pollution monitors throughout the U.S. The 1993 data disclose changes for the 1984-93 period and indicate significant improvements in the concentrations of all pollutants tested:
- Ground-level ozone decreased 12%.
- Lead decreased 89%.
- Sulfur dioxide (SO2) dropped 26%.
- Carbon monoxide (CO) declined 37%.
- Nitrogen dioxide (NO2) levels fell 12%.
- Particulate matter smaller than 10 Y (PM-10) has decreased 20% since 1988.
The report, titled "National Air Quality and Emissions Trends Report, 1993," also reveals that 1993 was the second consecutive year in which no U.S. cities violated the NO2 standard.
NONATTAINMENT AREAS
When the Clean Air Act Amendments of 1990 were passed, 140 million Americans were living in areas out of attainment for ground-level ozone. That number has since fallen to 43 million.
Of the 91 areas designated nonattainment" for smog in 1990, 48 now meet the standard. In addition, 28 of the original 38 areas designated nonattainment for CO now meet that standard.
The EPA says these areas are eligible for redesignation to attainment status." To date, however, only a handful of areas have actually been redesignated.
Since the original Naaqs designations, the 16 areas redesignated to "attainment" include:
- Five for ozone (Kansas City; Cherokee County, S.C.; Greensboro, N.C.; Knoxville, Tenn.; and Raleigh-Durham, N.C.)
- Four for CO (Cleveland; Duluth, Minn.; Syracuse, N.Y.; and Memphis)
- Seven for SO2 (Colbert County, Ala.; Green Bay, Wis.; Lauderdale County, Ala.; Dane County, Wis.; Milwaukee County, Wis.; Washington County, Ohio; and Morgan County, Ohio).
In contrast, 13 new areas have been designated nonattainment for PM-10 (including New York City and Sacramento and San Bernadino Counties in California), and three areas have been added to the list of areas out of attainment for SO2.
The EPA's report says compliance with national air quality standards is only the first step in achieving attainment status:
"Attainment is a legal definition that determines whether an area is subject to cleanup requirements of the Clean Air Act. Before these areas can be officially redesignated to attainment, EPA must approve their state clean air plans as well as their plans to stay in compliance with the standards for the next 10 years.
"Until these areas get an official attainment designation from EPA, they are still subject to all pertinent requirements of the [Clean Air] Act, such as programs for carpooling, clean fuel, and auto inspection maintenance. EPA plans to work closely with states and review their clean air plans (called state implementation plans, or SIPs) as expeditiously as possible."
OZONE
Ground-level ozone is the primary constituent of smog. And emissions of volatile organic compounds (VOCs) contribute to ozone formation.
Fig. 1(38715 bytes) shows U.S. VOC emissions for the 10-year period. New statistical techniques that take into account meteorological influences were used to determine changes for the period.
Between 1984 and 1993, a decrease of 12% was calculated for the second-highest daily maximum value collected during I hr. Over the 1992-93 period, the data indicated a 2% increase in that value. EPA attributes this increase to the fact that 1992 was a relatively low year for ozone.
In terms of the number of days during which the maximum was exceeded, a 60% decrease was calculated for the 10-year period.
EPA says VOC emissions have decreased 9% for the 10-year period, and increased 1% for the 1992-93 period.
Table 1(46444 bytes) shows VOC emissions by source category. The contribution of highway vehicles to total VOC emissions has declined from 37% in 1984 to 26% in 1993. The absolute reduction in VOC emissions from highway vehicles totaled more than 3 million tons/year over the I O-year period.
The contribution of petroleum and related industries to VOC emissions decreased from almost 5% in 1984 to 3% in 1993.
LEAD
Lead concentrations in ambient air have declined 89% for the 10-year period and 11% for the most recent 1-year period. Total lead emissions decreased 88% for the 10 years and increased 3% for the I-year period.
Over the same periods, lead emissions from transportation sources have decreased, respectively, 96% and 3%.
Thirteen areas remain designated nonattainment for lead. "Current lead nonattainment problems are associated with point sources, such as smelters, battery plants, and solid waste disposal," said EPA. "Consequently, EPA's lead attainment strategy targets airborne emissions from these stationary sources of lead."
Fig. 2 (33839 bytes) shows the trend in the annual average of quarterly maximum lead concentrations.
SULFUR DIOXIDE
Mean air concentrations of SO2 have decreased 26% over the 10-year study period, and 1% over the most recent year.
SOx emissions have decreased 6% for the 10-year period and increased 1 % for the 1-year period.
The reason air concentrations have improved out of proportion to the decrease in emissions, according to EPA, is that ambient air monitors are located in urban areas, while major emission sources tend to be in less populated areas.
The recent emissions increase was the result of increased fuel usage - primarily coal - in the electric utility industry. This increase was largely offset by reduced combustion of industrial fuel and decreased estimates of highway vehicle emissions.
EPA says almost all its urban areas meet Naaqs for 502. There are still, however, 47 areas designated nonattainment for SO2.
CARBON MONOXIDE
CO air concentration exceedances for 8-hr monitoring periods decreased 97% for the 10-year period. EPA also collects "8-hr second high" values, which decreased 37% for the 10 years and 5% for the most recent 1-year period.
CO emissions have declined 15% for the 10-yea period and increased 1% for the most recent 1-year period. The increase is due t vehicles - both highway an off-highway-and wildfires according to the report.
EPA says these improvements agree closely with it estimated 2% reduction i emissions from highway vehicles. In addition, these improvements occurred despite a 33% increase in the number of miles traveled during the past 10 years.
Fig. 3 (37053 bytes) shows CO emissions for the 10-year period ending in 1993. In 1993, says EPA, transportation sources accounted for 77% of total U.S. CO emissions.
Table 2 (47486 bytes) shows CO emissions by source category. The contribution of highway vehicles to total CO emissions decreased from 69% in 1984 to about 62% in 1993.
Petroleum and related industries contributed less than 0.5% to the total during the entire study period.
PARTICULATE MATTER
Data for the 10-year period show a 20% decrease in air concentrations of particulate matter and a 10% decrease in emissions (excluding miscellaneous and natural sources). For the 1992-93 period, decreases of 3% in air concentrations and 2% in emissions are reported.
The EPA report states "Progress in reducing particulate matter emissions i most noticeable in the area of highway vehicles, particularly diesel vehicles, and residential wood combustion."
Additionally, says EPA "Nationally, fugitive sources such as emissions from agricultural tilling, construction,
and unpaved roads contribute six to eight times more PM-10 emissions than sources historically included in emission inventories."
NITROGEN DIOXIDE
Air concentrations of NO2 have decreased 12% for the 10-year period and 2% for the 1-year period. NO, emissions for the two periods have increased, respectively, 1% and 2%.
According to the report, emissions from highway vehicles have declined 11% since 1984, while fuel combustion emissions increased by 3%. "About 76% of the increase in NOx emissions between 1992 and 1993 is attributable to increased emissions from coal-fired electric utilities," said EPA in the report. Off-highway sources are responsible for the remainder of the increase.
Although Los Angeles is the only area designated nonattainment for NO2, 1993 was the second consecutive r that all met the federal standard.
Recent information has shown that control of NO emissions is necessary to effectively reduce ozone in many areas, according to the report. Thus, said EPA "Even though the NO2 standards are now being met a all monitoring locations throughout the country, NO, emissions and their control are important factors for addressing the current widespread violations of the ozone Naaqs."
PROGRESS
These data indicate substantial progress toward meeting air quality goals. EPA Administrator Carol Browner said, "This year's trends report is encouraging news that our efforts are yielding results." These remarkable results were achieved before widespread use of oxygenated and reformulated gasolines. But, despite this progress, attainment statuses have changed little, and EPA continues to impose the strictest possible controls as though the environment were continuing to deteriorate.
EPA says it is using new information to continue improving air quality monitoring networks, air quality standards, and statistical techniques.
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