Open AccessSensitivity of the NO y budget over the United States to anthropogenic and lightning NO x in summer
Author(s) -
Fang Y.,
Fiore A. M.,
Horowitz L. W.,
Levy H.,
Hu Y.,
Russell A. G.
Publication year - 2010
Publication title -
journal of geophysical research: atmospheres
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.67
H-Index - 298
eISSN - 2156-2202
pISSN - 0148-0227
DOI - 10.1029/2010jd014079
Subject(s) - chemical transport model , environmental science , lightning (connector) , troposphere , atmospheric sciences , middle latitudes , plume , ozone , nitrogen oxides , tropospheric ozone , nitrogen oxide , reactive nitrogen , latitude , emission inventory , deposition (geology) , nox , meteorology , climatology , nitrogen , air quality index , geography , geology , chemistry , physics , power (physics) , waste management , engineering , paleontology , geodesy , quantum mechanics , combustion , organic chemistry , sediment
We examine the implications of new estimates of the anthropogenic and lightning nitrogen oxide (NO x ) source for the budget of oxidized nitrogen (NO y ) over the United States in summer using a 3‐D global chemical transport model (Model of Ozone and Related Tracers‐4). As a result of the Environmental Protection Agency (EPA) State Implementation call, power plant NO x emissions over the eastern United States decreased significantly, as reflected by a 23% decrease in summer surface emissions from the 1999 U.S. EPA National Emissions Inventory to our 2004 inventory. We increase the model lightning NO x source over northern midlatitude continents (by a factor of 10) and the fraction emitted into the free troposphere (FT, from 80% to 98%) to better match the recent observation‐based estimates. While these NO x source updates improve the simulation of NO x and O 3 compared to the Intercontinental Chemical Transport Experiment‐North America aircraft observations, a bias in the partitioning between nitric acid (HNO 3 ) and peroxyacetylnitrate (PAN) remains especially above 8 km, suggesting gaps in the current understanding of upper tropospheric processes. We estimate a model NO y export efficiency of 4%−14% to the North Atlantic in the FT, within the range of previous plume‐based estimates (3%−20%) and lower than the 30% exported directly from the continental boundary layer. Lightning NO x contributes 24%−43% of the FT NO y export from the U.S. to the North Atlantic and 28%−34% to the NO y wet deposition over the United States, with the ranges reflecting different assumptions. Increasing lightning NO x decreases the fractional contribution of PAN to total NO y export, increases the O 3 production in the northern extratropical FT by 33%, and decreases the regional mean ozone production efficiency per unit NO x (OPE) by 30%. If models underestimate the lightning NO x source, they would overestimate the background OPE in the FT and the fractional contribution of PAN to NO y export. Therefore, a model underestimate of lightning NO x would likely lead to an overestimate of the downwind O 3 production due to anthropogenic NO x export. Better constraints on the lightning NO x source are required to more confidently assess the impacts of anthropogenic emissions and their changes on air quality over downwind regions.