Comparison of emissions of nitrogen and sulfur oxides to deposition of nitrate and sulfate in the USA by state in 1990

Many naturally occurring and human-induced activities result in the emission of nitrogen- and sulfur-containing compounds into the atmosphere. Precipitation is an important process by which compounds are scavenged from the atmosphere and deposited onto the earth's surface. The purpose of this paper is to compare the emissions of nitrogen oxides (NOx) and sulfur dioxide (SO2) in each of the 48 contiguous states in the USA with measured wet deposition of nitrate (NO3-) and sulfate (SO42-) in each state for the year 1990. With one exception (Vermont), wet deposition of N as nitrate was less than emissions of N as nitrogen oxides on a statewide basis in 1990. The median wet N deposition/emission value was 0.21. Wet plus dry N deposition of nitrate was estimated to represent 43% of NOx emissions in North Carolina. Wet deposition of S was less than emissions in 1990 in all but five states (Vermont, Maine, Arkansas, Nebraska, and South Dakota). The median value of wet deposition of sulfate/SO2 emissions was 0.34. In North Carolina, dry deposition of sulfate was estimated to represent an additional 21% of emissions, so that total deposition accounted for 60% of S emissions. Net transport of N and S is likely an important part of the discrepancy between emissions and deposition.