Emissions Background and Rationale North American SO 2 Emission Rates North American NO x Emission Rates Contact: Bret Schichtel,

Background and Rationale Knowledge of PM emissions is used for source apportionment and control measures The majority of the PM2.5 mass over the US is of secondary origin, formed within the atmosphere through gas-particle conversion of precursor gases such as sulfur oxides, nitrogen oxides and organics. Precursor emissions that are well defined include sulfur (SO2) and nitrogen (NOx) while the emissions of other species such as organics, soil, and soot are poorly defined.

North American SO 2 Emission Rates The highest emission rates occur over the Ohio River Valley, eastern seaboard, and urban locations, such as Atlanta and St. Louis.

US American NO x Emission Rates Area source NO x emissions are highest near cities. Point source emissions are highest over the Industrial Midwest.

On the Origin PM2.5 in the Atmosphere - [Fragment] At this time, the most reliable means of identifying the origin of PM2.5 is the chemical analysis of the the PM samples which reveals that most of PM2.5 is composed of secondary sulfates, organics and nitrates. Identifying the PM2.5 precursor sources is elusive since they occur 100 or 1000 miles from the receptor. Also, the chemical transformations involve many factors including photochemical oxidants and cloud interactions. Primary PM2.5 such as soot and fine dust can be traced based on chemical signatures since each PM source type produces particles with specific physical, chemical and optical signature. Contact: Rudolf Husar,

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