In 1996, Massachusetts discontinued lead (Pb) monitoring because air quality levels were well below the NAAQS and at the lowest levels of method detection. In 1997, nitrogen dioxide (NO2) measurements were made at thirteen monitoring sites throughout the Commonwealth. The highest annual average concentrations were recorded in the Metropolitan Boston area, Worcester, and Springfield. The lowest concentrations were recorded at the rural sites of Newbury-Plum Island and Quabbin Summit. The rural sites recorded average annual concentrations of 0.007 ppm and 0.009 ppm, respectively. The Kenmore Square monitoring station recorded the highest 1997 average annual NO2 concentration of 0.030 ppm. Yearly variability for the Massachusetts average annual NO2 data is small. Also, over the past ten years, there has been no apparent upward or downward trend for the sites.
Sixteen ozone monitoring sites were operated and maintained during the 1997 summer ozone season. Three monitoring sites recorded ozone concentrations above the NAAQS. Ozone concentrations recorded in 1997 were generally higher than those recorded in 1996. The higher ozone concentrations in 1997 may be due to the warmer, drier summer of that year. The highest ozone concentrations were recorded at the Quabbin Summit (0.151 ppm) and Fairhaven (0.145) monitoring sites. Over the past ten years, the maximum concentration of ozone and the frequency of concentration in excess of the ozone NAAQS have fluctuated. This has been due to changes in the emission of ozone precursors and changes in meteorology.
There are sixteen particulate matter (PM10) monitoring sites in Massachusetts. All of the sites, with the exception of the Quabbin Summit and Sudbury sites, are located within urban areas of the Commonwealth. The highest annual average concentrations of PM10 were recorded in Springfield-East Columbus (29 µg/m3), Boston-Columbus (26 µg/m3), and Boston-Kenmore Square (25 µg/m3). The highest maximum and second highest maximum 24-hour PM10 concentrations were recorded at Boston-One City Square (110 µg/m3). In contrast, the lowest annual concentration was recorded at Quabbin Summit (11 µg/m3). Over the past 10 years, the concentrations of PM10 at the urban sites have shown considerable data variability. The Boston-Kenmore Square and Worcester sites have shown a general downward trend in PM10 concentrations. The other sites, excluding the non-urban sites, have shown significant year-to-year variability with no apparent upward or downward visible trends. The Quabbin Summit site has shown a general reduction in the average annual concentration of PM10.
Nineteen sulfur dioxide (SO2) monitoring sites were operated in Massachusetts during 1997. There were no violations recorded of the annual, 24-hour (primary) or 3-hour (secondary) NAAQS for SO2. The highest short-term (3-hour) SO2 concentrations were recorded at the Swansea monitoring site (108 ppb). The Chelsea site recorded the maximum 24-hour concentration of 55 ppb. The second maximum 24-hour concentration of 44 ppb was recorded at the Swansea site. The lowest annual average SO2 concentration, recorded at several sites, was 4 ppb. The highest annual SO2 concentration was recorded in Boston-Kenmore Square (9 ppb). Over the past ten years, all SO2 monitoring sites in Massachusetts have shown a general decline in SO2 levels.