Global Natural Emissions Estimates from MPAS-CMAQ

The recent decline of anthropogenic air pollution precursors motivates more accurate quantification of natural emissions sources. The U.S. EPA’s Community Multiscale Air Quality (CMAQ) model currently estimates natural contributions to tropospheric burdens of biogenic VOCs, soil NO, windblown dust, stratospheric ozone, lightning NO, sea spray aerosols, marine halogens, and dimethyl sulfide (DMS). Coupling the Model for Prediction Across Scales (MPAS) with CMAQ (MPAS-CMAQ) allows for the first global accounting of CMAQ’s online emissions. Here, we present estimates of natural sources from CMAQ and contextualize regional and seasonal performance with ranges from other modeling studies. We quantify sensitivities to resolution, meteorological variability, and configuration options.

Results show that CMAQ’s biogenic emissions module MEGAN v3.2 overestimates some BVOC species, such as monoterpenes, and underestimates others, such as isoprene. Soil NO emissions range from underestimated to overestimated depending on configuration options selected. The windblown dust parameterization produces annual emissions of coarse mode soil ranging from 173-284 Tg/yr. Annual stratospheric ozone transport into the troposphere averages a reasonable 524 Tg/yr. Coarse mode sea salt aerosols, dominated by the Southern Hemisphere, range from 955-982 Tg/yr. Annual marine halogen emissions compare well with the global annual estimates in published studies, including 562 Gg of CHBr3, 1401 Gg of inorganic iodine, and 16,494 Gg of sulfur (GgS) from DMS. We discuss planned improvements to each of these parameterizations within CMAQ.

Disclaimer: The views expressed in this abstract are those of the authors and do not necessarily represent the views or policies of the U.S. Environmental Protection Agency (EPA).