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 emissio n of nitrogen- and sulfur-containing compounds into the atmosphere. Precipi tation is an important process by which compounds are scavenged from the at mosphere and deposited onto the earth's surface. The purpose of this paper is to compare the emissions of nitrogen oxides (NOx) and sulfur dioxide (SO 2) in each of the 48 contiguous states in the USA with measured wet deposit ion 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 nitr ate 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 (Ver mont, Maine, Arkansas, Nebraska, and South Dakota). The median value of wet deposition of sulfate/SO2 emissions was 0.34. In North Carolina, dry depos ition of sulfate was estimated to represent an additional 21% of emissions, so that total deposition accounted for 60% of S emissions. Net transport o f N and S is likely an important part of the discrepancy between emissions and deposition.