NATURAL EMISSIONS OF OXIDANT PRECURSORS

This paper provides an overview of the sources, the estimation methodo logy, and the relative amounts of natural hydrocarbon and NO(x) emissi ons. The most recent estimate of natural nonmethane hydrocarbon (NMHC) emissions for the United States is 28 Tg yr-1. This compares with 20 Tg yr-1 for anthropogenic NMHC sources. The southeastern and southcent ral portions of the United States account for approximately 43% of the annual U.S. natural NMHC estimate. These emissions exhibit strong diu rnal and seasonal dependencies related to temperature, solar radiation , and active biomass. Forests are the primary vegetative source of hyd rocarbons. The major sources of natural NO(x) emissions in North Ameri ca are biomass burning, lightning, and microbial activity in soil. We present a comparison of hourly gridded NO(x) emissions from lightning, soil, and man-made sources for the northeastern United States. We als o provide results from preliminary investigations of the sensitivity o f O3 predictions from the U.S. Environmental Protection Agency's Regio nal Oxidant Model to natural NMHC and nitric oxide emissions. Disclaim er: This paper has been reviewed in accordance with the U.S. Environme ntal Protection Agency's peer and administrative review policies and a pproved for presentation and publication. Mention of trade names or co mmercial products does not constitute endorsement or recommendation fo r use.