Sulfates and Nitrates

Sulfates and Nitrates are compounds of varying harmfulness found everywhere in the atmosphere. They are produced by nature as well as by man. Man-made sulfates have their origin in sulfur dioxide while nitrates have theirs in nitrogen oxides. Fine particulate compounds, including sulfates and nitrates are formed from chemical reactions between sulfur dioxide or nitrogen dioxide emitted into the air and other substances present there. These fine particulate compounds have a long atmospheric residence time, can be transported in the air for long distances, and are capable of penetrating deeply into the human respiratory tract.

Epidemiological studies of populations exposed to particulate sulfates have shown that atmospheric sulfates, more than sulfur dioxide gas or total suspended particulates, are related to aggravation of asthma, aggravation of heart and lung disease in the elderly, and impairment of lung function in school children. This evidence was obtained from EPA's Community Health and Environmental Surveillance System (CHESS). From these studies, estimates of sulfate threshold for adverse health effects have been derived, as shown in Table 21. However, these epidemiological studies have not been substantiated by laboratory studies.

Both sulfates and nitrates are considered to be contributors to the acid deposition problem. There are currently no standards for levels of sulfates or nitrates in ambient air.

Sulfate and nitrate levels are currently measured at six sites in Maine as part of the overall analysis of filters used in the speciated particulate network in Maine . The six monitors, which are part of the IMPROVE (Interagency Monitoring of Protected Visual Environments), are located in Bridgton, Freeport , Bar Harbor, Old Town , Baring and Presque Isle. In addition, there is a continuous sulfate monitor operated at the site in Bar Harbor . Data from the continuous monitor in Bar Harbor is available on the air quality web site. Data collected by the IMPROVE program can be viewed at the IMPROVE web site, at http://vista.cira.colostate.edu/impr o ve/Data/data.htm . IMPROVE and other haze related data are also available on the VIEWS web site, at http://vista.cira.colostate.edu/views / .

 

 

 

 

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