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Improving the Characterization of the Natural Emissions in CMAQ
Citation:
Kang, D., J. Willison, G. Sarwar, M. Madden, C. Hogrefe, R. Mathur, B. Gantt, AND S. Alfonso. Improving the Characterization of the Natural Emissions in CMAQ. EM Magazine. Air and Waste Management Association, Pittsburgh, PA, (10):1-7, (2021).
Impact/Purpose:
Natural emission sources that produce nitrogen oxides (NOx) and biogenic VOCs contribute to the tropospheric ozone (O3) formation and other air quality related processes. To quantify the complex impacts of natural emissions on air quality, chemical transport models must include realistic characterizations of the source strengths, spatial and temporal distributions of the emissions, and evolution of the emitted species from natural sources due to climate change. Recent updates to the U.S. Environmental Protection Agency’s (EPA’s) Community Multiscale Air Quality (CMAQ) modeling system have included improvements to the emission and chemistry of natural emissions.
Description:
The air quality of any given location is the result of complex interactions between meteorology and emissions through dynamical, physical, chemical, and photochemical processes. Of the many sources of air pollution, naturally produced emissions such as nitric oxide (NO) from soil[1] and lightning[2], biogenic volatile organic compounds (BVOCs)[3] from vegetation, and sulfur dioxide (SO2) and carbon dioxide (CO2) from volcanic eruptions[4] constitute a nonnegligible and relatively stable portion of the total emissions of these pollutants. Despite the decreasing trend of anthropogenic emissions in the United States (U.S.), surface-level ozone (O3) concentrations have not subsequently decreased in many regions including the Mountain West and the Pacific Coast[5]. This seemingly contradictory result was further revealed by the lockdowns instituted to control the coronavirus disease 2019 (COVID-19) pandemic. During that period in the Spring of 2020, surface O3 levels increased by up to 50% in some locations despite large and widespread reductions in loading from fossil fuel NO emissions associated with vehicles[6]. In addition to the nonlinear atmospheric chemistry under decreasing anthropogenic emissions, changes in the relative contribution of natural emissions to the total emissions budget in the atmosphere become increasingly important[7]. For example, the oceanic emissions of iodine have tripled since 1950, driven by anthropogenic O3 pollution and rising temperatures, as registered by Arctic and Alpine ice cores and tree ring measurements[8-10]. To quantify the complex impacts of natural emissions on air quality, chemical transport models must include realistic characterizations of the source strengths, spatial and temporal distributions of the emissions, and evolution of the emitted species from natural sources due to climate change. Recent updates to the U.S. Environmental Protection Agency’s (EPA’s) Community Multiscale Air Quality (CMAQ) modeling system have included improvements to the emission and chemistry of natural emissions. In this paper, we summarize the updates to lightning NOx (LNOx), BVOCs, soil NOx (SNOx), and halogen emissions in CMAQ and their impacts on model predicted surface O3.