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Air Quality in New England Contents:
There currently exist several air quality monitoring programs aimed at developing quantitative measures of air quality through the analysis of a variety of chemical species in the atmosphere. Among these are the National Atmospheric Deposition Program (NADP), which has been monitoring the acidity and chemical content of precipitation throughout the United States for the past two decades and the Environmental Protection Agency's -Photochemical Assessment Monitoring Stations (PAMS), which provide an air quality data base for dealing with ozone and other criteria pollutants . Programs such as these, in combination with several smaller scale research and monitoring projects, provide the basis for monitoring the quality of the air we breathe. Tracking Air-Masses Affecting New England Using Chemical Tracers While many atmospheric parameters (such as temperature, sunlight, precipitation, humidity, etc.) influence the composition of air-masses, natural and anthropogenic emissions in the source regions remain one of the most critical for determining the chemical fingerprint of an air-mass. Air chemistry monitoring therefore represents a valuable tool for identifying the source region for various air-masses. To better identify the source regions for air-masses traveling to New England and their influence on the region's air quality, aerosol and precipitation chemistry is currently being investigated at the Mount Washington Observatory and on the New Hampshire Seacoast at Odiorne Point, Rye by the Climate Change Research Center. Below we provide several examples of the intimate link between air-mass source regions and air chemistry in New England. Aerosol Chemistry on New Hampshire's Seacoast The New Hampshire seacoast lies downwind of the major metropolitan centers and transportation corridors in New England, and therefore provides a suitable site to investigate the impact of both local and distant sources of pollution. At Odiorne Point, aerosols are collected daily on Teflon filters and analyzed for their soluble major ion chemistry (sodium, ammonium, potassium, magnesium, calcium, chloride, nitrate and sulfate). Aerosols with distinct chemical compositions originate from different source regions and can therefore be used to "fingerprint" different air-masses. Daily weather maps made available by the National Oceanic and Atmospheric Administration (NOAA) are also analyzed to determine air flow patterns and thereby identify potential source regions. Through this combined approach of investigating physical and chemical climate, air chemistry data can be used to determine the source regions of various air-masses. Figure 4.1 shows some of our preliminary results from aerosol samples collected over two months during the spring of 1998. Marine air-masses (those coming from the east) show high levels of sea salt (composed primarily of sodium and chloride); air-masses from the eastern seaboard south of New England show high levels of acidic species, indicative of anthropogenic emissions from the burning of fossil fuels in the mid-Atlantic states; and air-masses from Canada show very low sea-salt, indicative of their continental origin, but high sulfate, perhaps originating from the smelting of sulfur rich ores in the Sudbury region of Ontario (Clark, 1980). Air-masses from the northwest (i.e., those originating in Canada) also show high levels of ammonium, likely reflecting agricultural sources from rural areas to the northwest of New Hampshire's seacoast (Lefer, 1997). Rime-Ice Chemistry on Mount Washington In February of 1998, rime-ice samples were collected at the summit of Mount Washington to investigate how air-masses from different geographic regions affect the precipitation chemistry, and hence air quality, over Mount Washington. The summit of Mount Washington was chosen as a study site because it is one of the most remote locations in New England and is situated at the intersection of three of North America's major storm tracks. As such, the summit of Mount Washington is an ideal location to study how emissions emanating from other regions of the country affect the chemical climate of northern New England. The results from the Mount Washington study are complementary to those from Odiorne Point. There was a distinct change in concentration of sea-salt, nitrate, non sea-salt (nss) sulfate, and ammonium in rime-ice at Mount Washington on 21 February 1998 (Figure 4.2). The change in rime-ice chemistry is due to a shift in air-mass source region from a southwest trajectory out of the Ohio River Valley during the morning to a west-northwest trajectory out of Ontario, Canada in the afternoon. Rime-ice from the southwesterly derived air-mass contained elevated concentrations of nitrate and nss sulfate likely reflecting emissions from coal- and oil-burning power plants and mobile sources (e.g., cars and trucks) in the Ohio River Valley. The shift to a west-northwest air-mass trajectory was coincident with a decrease in the concentration of nitrate and an increase in concentration of nss sulfate, perhaps reflecting anthropogenic sources in the Great Lakes industrial region and/or Sudbury, Ontario. This "Canadian" air-mass also shows higher levels of ammonium, consistent with agricultural sources to the northwest of Mount Washington. Continued monitoring of a wide variety of air quality parameters on the seacoast, at Mount Washington, and at several other sites throughout the state will allow us to develop a much better understanding of the relationship between air quality in New England and the transport of pollution from upwind sources into the region. Acid rain and the Environmental Impact of the Clean Air Act Precipitation chemistry records derived from a Greenland ice core (Figure 1.3, Mayewski et al., 1990) reveal a dramatic increase in the concentrations of sulfate and nitrate following the industrial revolution (approximately 1900 AD), as mentioned in Chapter One. The Greenland ice core record also shows a leveling off of sulfate and nitrate concentrations after 1970 when the National Ambient Air Quality Standards (NAAQS) were established as part of the Clean Air Act . The 1970 amendments to the Federal Clean Air Act were developed to protect the public's health and welfare by controlling air pollution at its source through the establishment of primary and secondary NAAQS. Since 1970 several amendments have been made establishing stricter primary and secondary NAAQS as a result of a better understanding of the impact that air pollutants have on human health and the environment. Acid rain is caused primarily by the emission of sulfur dioxide (SO2) and nitrogen oxides (NOx) from the combustion of fossil fuels that we use to heat our homes, power our cars, generate electricity, and run our factories. Here in the Northeast, this phenomenon has caused lakes and stream to become unsuitable for many fish (Baker and Schofield, 1985; Park, 1987). Acid rain has been known to leach heavy metals such as mercury from rocks, thereby causing contamination of water supplies and introducing human health risks (Brakke et al., 1988). Acid rain can also alter soil chemistry in agricultural and forested lands and causes significant damage to human made structures, especially those consisting of limestone and marble. In addition to contributing to acid rain, sulfate aerosols also play a significant role in Earth's radiation balance. The increase in sulfate aerosol in the troposphere adjacent to industrial regions of the globe over the past century has in fact served to cool climate on a regional scale (Charlson et al., 1992; Mayewski et al., 1993, IPCC, 1995). How has the Clean Air Act affected the acid rain problem in the northeast? Aerosol chemistry samples from Whiteface Mountain in upstate New York show a strong correlation between the decrease in SO2 emissions in the mid-western states since 1970 and the decrease in average sulfate concentrations in the Northeast (Husain et al., 1998). The deposition of sulfate in precipitation in northern New England measured at four locations has decreased on the order of 30% since the early 1980s ( Figure 4.3a ). In addition, the longest precipitation chemistry record in New England, measured at Hubbard Brook in northern New Hampshire, shows that the average pH of precipitation has increased since 1970 from approximately 4.1 to 4.3 standard pH units ( Figure 4.4 ), indicating that the acidity of precipitation is slowly decreasing. The same cannot be said for the deposition of nitrate, which has shown no significant change since the early 1980s (Figure 4.3b ). The decrease in sulfate deposition and precipitation acidity can be directly linked to the reduction in SO2 emissions as a result of the Clean Air Act. In fact, annual SO2 emissions from anthropogenic sources in the U.S. have decreased from 28.3 million metric tons in 1970 to 17.4 million metric tons in 1996 (Figure 4.5 ). This is due primarily to a reduction in sulfur emissions from electric utilities, which are responsible for approximately two-thirds of the nation's sulfur emissions. At the same time, nitrogen oxides emission rates have increased from 19.7 million metric tons in 1970 to 21.3 million metric tons in 1996. This increase can largely be related to the more than doubling of vehicle miles traveled over the past three decades. (U.S.EPA, 1977). Motor vehicles currently account for approximately 30% of all nitrogen oxides emissions. Clearly, the Clean Air Act Amendments have been successful in reducing sulfur oxides emission rates and sulfate deposition via precipitation. On the other hand, nitrogen oxides emission rates have continued to increase, albeit slowly, and wet deposition of nitrate has remained relatively constant. Amendments to the Clean Air Act that were designed to reduce emissions of criteria pollutants further were passed in 1990 and were phased in starting in 1995. Ongoing air quality monitoring and research programs will evaluate the effect of the 1995 amendments on air quality in coming years. Ozone in New England Ozone is a very important chemical in our atmosphere. It is found in the troposphere (near the earth's surface, where our weather occurs) as well as in the stratosphere (above the troposphere). Ozone in the stratosphere protects us from ultraviolet radiation. Scientists are concerned about the depletion of this ozone layer, particularly the ozone "hole" over Antarctica, as well as the more recent depletion in northern latitudes. Ozone in the troposphere affects us very differently. Tropospheric ozone, a component of urban smog, causes health problems for humans and ecosystems. In high concentrations for periods of a few hours, ozone can damage lung tissue, reduce lung function, irritate eyes, and is also harmful to plants. Tropospheric ozone is a pollutant which affects large geographical areas when weather conditions are favorable for its formation. Ozone at ground-level is a secondary pollutant which forms in the atmosphere as a by-product of chemical reactions that take place between other chemical compounds (i.e. ozone precursors) emitted from automobiles, diesel trucks and industrial sources. Specifically, these ozone precursors are volatile organic compounds (VOCs) and oxides of nitrogen (NOx). These compounds react together when exposed to strong ultraviolet radiation from the sun during hot summer weather. Ozone, NOx , and VOCs are currently monitored by State Environmental Agencies. Several stations have been established in New England since several cities in the region (including the Dover-Portsmouth-Rochester region) are designated as "serious non-attainment zones" for ozone by the EPA. Very high ozone levels occur in the seacoast regions of Maine, New Hampshire, and Massachusetts during the summer due to a combination of factors. These areas are densely populated and produce an abundance of pollution themselves. The area also tends to be sunny in spring and summer because of the sea breeze effect, which inhibits cloud formation. However, ozone levels tend to rise to their highest and most unhealthy levels when pollutants are transported into New England from regions to the southwest along what is known as the ozone transport corridor. In 1997, the EPA changed its criteria for unhealthy ozone levels. Instead of hourly ozone levels exceeding 120 parts per billion (ppb), an 8-hour average of over 80 ppb is now considered an "exceedance". Some individuals may be affected by short periods of very high ozone, but it is more harmful for most people and for plants to be exposed for longer periods of time, even at a lower level. This change in standards resulted in more events being classified as very unhealthy (Figure 4.6 ). The high number of unhealthy ozone days in 1988 is remarkable. This is primarily attributed to a circulation pattern which brought several periods of hot sunny weather to the Northeast. This circulation pattern was linked to a phenomenon in the southern Pacific ocean called La Niña , which often follows a prolonged El Niño event. Interestingly, climate events halfway around the world have a significant effect on our region's air quality. On average, southern New Hampshire and coastal Maine experience 3 to 5 days per year of very unhealthy ozone levels, with some years (e.g., 1988) that are considerably worse. However, high ozone levels are not restricted to these areas. In fact, very unhealthy levels of ozone have also been measured by the Appalachian Mountain Club (AMC) at the summit of Mount Washington. What is the anatomy of a high ozone event in New England? Below, we provide 3 examples of ozone events in New Hampshire to illustrate what we know and what we do not concerning the causes of high ozone events in the region. 1. High Ozone along the East Coast, June 28-July 1, 1997 : On 28 June a high pressure center to the west of New England yielded sunny skies (Figure 4.7a ). Pollutants from the seacoast reacted with sunlight to form ozone. However, by 1 July, ozone levels increased by an additional 50%. Why this increase? As the high pressure system moved eastwards, the prevailing winds shifted from a northwest to a southwest direction, transporting pollutants and already-formed ozone from other industrial areas to the southwest and along the east coast of the U.S. ( Figure 4.7b ), adding to already high ozone levels. The influence of ozone transported into coastal New Hampshire and Maine is clearly illustrated in Figure 4.8 . Ozone and its precursors move with the weather systems and ozone formed as a result of New York or Boston emissions can impact populations in New Hampshire and Maine on a hot summer day. The highest ozone levels of the day typically occurs late in the afternoon at monitoring stations most susceptible to long range transport. Coastal ozone monitors in New Hampshire and Maine usually record the highest ozone concentrations as a result of transport over the open ocean from the big cities to the south. Wind direction on a hot summer afternoon will determine if ground-level ozone is going to be a problem on a particular day. In addition, peak values for ozone rise steadily from 28 June to 1 July, as more polluted air is transported into the region ( Figure 4.9 ). Note that the trend in NO2, one chemical compound which contributes to ozone formation, shows a trend which is opposite to that for ozone (i.e., low values during the afternoon when ozone levels are greatest). This illustrates NO2 consumption during the series of reactions that lead to the formation of ozone. 2. High Ozone at Portsmouth and Mt. Washington, 11 July 1988: This was a period of very high ozone on the seacoast as well as on the summit of Mount Washington ( figure 4.10 ). As usual, the seacoast levels drop dramatically at night as tropospheric ozone was effectively removed from the atmosphere close to the ground and because it is not produced after the sun goes down. Atop Mount Washington, though, the readings remained very high, actually peaking in the early morning on the 11th, and not dropping below 70 ppb for three straight days. The White Mountain region is not a major pollutant source, and therefore the ozone was probably carried in on westerly winds. The lack of a diurnal variation is explained by the fact that there is very little ground surface at the summit of Mt. Washington, so ozone is not readily removed from the atmosphere. Note that ozone levels at the base of the mountain were much lower than at the summit, day and night, even though it is only four miles away. The dense forest environment at the base serves to rapidly remove ozone from the atmosphere. 3. High ozone only on Mount Washington, 4-5 July, 1989: Ozone levels on the summit of Mt. Washington peaked early on 5 July at about 130 ppb, well above normal and healthy levels. However, ozone levels at the base of the mountain and on the seacoast never exceeded 60 ppb. (figure 4.11 ) Why the difference between sites, and why did it peak in the early morning when ozone formation is normally highest in the afternoon? Perhaps a disturbance in the layer that separates the troposphere from the stratosphere allowed ozone from the stratosphere ("good" ozone, our protective shield) to accumulate for a short period at the summit of Mt. Washington, but was not transported to low elevations such as the base of Mt. Washington or the seacoast. This peak may also represent the long-range transport of ozone from the west or southwest at elevations of 5000 - 6000 feet (i.e., the summit elevation of Mount Washington), which would not influence ozone concentration on the seacoast. Future monitoring of a variety of both gas phase and aerosol chemistry will provide the data necessary to answer these and other important scientific questions regarding air quality in New England. Why continue to investigate air quality in New England? Clearly, our general understanding of chemical climate in New England over the past two decades improved substantially - especially with respect to acid rain and ozone. However, many of the specifics regarding air quality issues remain poorly understood. In conjunction with ongoing air quality monitoring programs in the region, we plan to develop a detailed air quality/air-mass trajectory data base in order to address several specific scientific questions, including:
References Baker, J.P., and Schofield, C.L. 1985. Acidification Impacts on Fish Populations: A Review. In D.D. Adams and W.P. Page (eds), Acid Deposition: Environmental, Economic and Political Issues. Plenum Press: New York. Charlson, R.J., Schwartz, S.E., Hales, J.M., Cess, R.D., Coakley, J.A., Hansen, J.E., and Hoffman, D.J., 1992, Climate forcing by anthropogenic aerosols, Science 255:423-430. Clark, T.L. 1980. Annual anthropogenic pollutant emissions in the United States and southern Canada east of the Rocky Mountains. Atmos. Environ. 14:961-970. Husain, L., Dutkiewicz, V.A., and Das, M. 1998. Evidence for Decrease in Atmospheric Sulfur Burden in the Eastern United States Caused by Reduction in SO2 Emissions. Geophysical Research Letters 25:967-970. Intergovernmental Panel on Climate Change (IPCC) 1995. Climate Change 1995: The Science of Climate Change. Cambridge University Press. Lefer, B. 1997. The Chemistry and Dry Deposition of Atmospheric Nitrogen at a Rural Site in the Northeastern United States. Ph.D. Dissertation, University of New Hampshire: Durham, New Hampshire. Mayewski, P.A., Lyons, W.B., Spencer, M.J., Twickler, M.S., Buck, C.F. and Whitlow, S. 1990. An Ice Core Record of Atmospheric Response to Anthropogenic Sulphate and Nitrate. Nature 346: 554-556. Mayewski, P.A., Holdsworth, G., Spencer, M.J., Whitlow, S., Twickler, M., Morrison, M., Ferland, K., and Meeker, L.D. 1993. Ice-core Sulfate from Three Northern Hemisphere Sites: Source and Temperature Forcing Implications. Atmospheric Environment 27A:2915-2919. Park, C.C. 1987. Acid Rain: Rhetoric and Reality. Methuen: London. U.S. EPA. 1997. National Air Pollutant Trends, 1900-1996. Office of Air Quality Planning and Standards, Research Triangle Park, NC, EPA-454/R-97-011. Report by: Dr. Cameron Wake, Research Assistant Professor in the Climate Change Research Center in the Institute for the Study of Earth, Oceans and Space and the Department of Earth Sciences. Mr. Kevan Carpenter, Research Technician, Climate Change Research Center in the Institute for the Study of Earth, Oceans and Space. Mr. Justin Cox, Iola Hubbard Climate Change Endowment Undergraduate Summer Fellow. Mr. Joe Souney, Iola Hubbard Climate Change Graduate Summer Fellow. Mr. Paul Sanborn, New Hampshire Department of Environmental Services. Mr. Mark Rodgers, Department of Chemistry, University of New Hampshire. |
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