GLOBAL NOX, HNO3, PAN, AND NOY DISTRIBUTIONS FROM FOSSIL-FUEL COMBUSTION EMISSIONS - A MODEL STUDY

The 11-level Geophysical Fluid Dynamics Laboratory global chemical transport model (GCTM) which explicitly treats NO(x), HNO3, and PAN as transported species has been used to assess the impact of fossil fuel combustion emissions on the distribution of reactive nitrogen compounds (NO(y)) in various regions of the troposphere. The GCTM is driven by 6-hour time-averaged wind and total precipitation fields derived from a parent general circulation model. PAN production rates are calculated using background, two-dimensional ethane and propane fields, which are then adjusted to parameterize the effect of short-lived hydrocarbons over continental regions. From an analysis of our model results, we conclude that (1) the model reproduces the observed spatial patterns of wet deposition near the major fossil fuel combustion source regions. Wet and dry deposition in source regions account for 30% and 40-45% of the emissions, respectively, with the remainder being exported over the adjacent ocean basins; (2) the fossil fuel source accounts.for a large fraction of the observed surface concentrations and wet deposition fluxes of HNO3 in the extra tropical North Atlantic; (3) while it appears that a significant fraction of NO(y) observed in the marine free troposphere during the NASA Global Tropical Experiment/CITE 2 experiment in the eastern North Pacific cannot be explained in terms of the fossil fuel source, this may simply indicate that in this region subgrid-scale transport from adjacent continental source regions is not being adequately resolved by the model; (4) at the more remote Mauna Loa, Hawaii site, less than 30% of the observed NO(y) during May 1988, appears to be due to distant fossil fuel sources; (5) even with the explicit treatment of PAN as a transported species, the fossil fuel source has only a minor impact on NO(y) levels in the remote tropics and in the southern hemisphere; (5) model calculations indicate that the relatively high levels of NO(y) observed over western Alaska during the ABLE 3A experiment in July-August 1988, cannot be explained in terms of long-range transport of fossil fuel combustion emissions from the northern hemisphere mid-latitude surface source regions; and (6) away from source regions, PAN is a major component of fossil fuel NO(y), and is the dominant component poleward of 45-degrees-N. However, the relative impact of this sequestered PAN on regional spring time NO(x) levels has yet to be established.