Assessing the roles emission sources and atmospheric processes play in simulating δ 15 N of atmospheric NO x and NO 3 − using CMAQ (version 5.2.1) and SMOKE (version 4.6)

[摘要] Nitrogen oxides (NO x = nitric oxide (NO) + nitrogen dioxide(NO 2 )) are important trace gases that affect atmospheric chemistry, airquality, and climate. Contemporary development of NO x emissionsinventories is limited by the understanding of the roles of vegetation (netNO x source or net sink), vehicle emissions from gasoline- anddiesel-powered vehicles, the application of NO x emission controltechnologies, and accurate verification techniques. The nitrogen stableisotope composition ( δ 15 N) of NO x is an effective tool toevaluate the accuracy of the NO x emission inventories, which are basedon different assumptions. In this study, we traced the changes in δ 15 N values of NO x along the “journey” of atmospheric NO x ,driven by atmospheric processes after different sources emit NO x into theatmosphere. The 15 N was incorporated into the emission input dataset,generated from the US EPA trace gas emission model SMOKE (Sparse MatrixOperator Kernel Emissions). Then the 15 N-incorporated emission inputdataset was used to run the CMAQ (Community Multiscale Air Quality) modelingsystem. By enhancing NO x deposition, we simulated the expected δ 15 N of NO 3 - , assuming no isotope fractionation duringchemical conversion or deposition. The simulated spatiotemporal patterns inNO x isotopic composition for both SMOKE outputs (simulations underthe “emission only” scenario) and CMAQ outputs (simulations under the “emission + transport + enhanced NO x loss” scenario) were compared withcorresponding measurements in West Lafayette, Indiana, USA. The simulationsunder the emission + transport + enhanced NO x loss scenario werealso compared to δ 15 N of NO 3 - at NADP (NationalAtmospheric Deposition Program) sites. The results indicate the potentialunderestimation of emissions from soil, livestock waste, off-road vehicles,and natural-gas power plants and the potential overestimation of emissionsfrom on-road vehicles and coal-fired power plants, if only considering thedifference in NO x isotopic composition for different emission sources.After considering the mixing, dispersion, transport, and deposition ofNO x emission from different sources, the estimation of atmospheric δ 15 N(NO x ) shows better agreement (by ∼  3 ‰) with observations.

[学科分类] 土木及结构工程学