Sherri W. Hunt

A preliminary synthesis of modeled climate change impacts on U.S. regional ozone concentrations.

This paper provides a synthesis of results that have emerged from recent modeling studies of the potential sensitivity of U.S. regional ozone (O3) concentrations to global climate change (ca. 2050). This research has been carried out under the auspices of an ongoing U.S. Environmental Protection Agency (EPA) assessment effort to increase scientific understanding of the multiple complex interactions among climate, emissions, atmospheric chemistry, and air quality. The ultimate goal is to enhance the ability of air quality managers to consider global change in their decisions through improved characterization of the potential effects of global change on air quality, including O3 The results discussed here are interim, representing the first phase of the EPA assessment. The aim in this first phase was to consider the effects of climate change alone on air quality, without accompanying changes in anthropogenic emissions of precursor pollutants. Across all of the modeling experiments carried out by the differe...

Updating the Conceptual Model for Fine Particle Mass Emissions from Combustion Systems

Abstract Atmospheric transformations determine the contribution of emissions from combustion systems to fine particulate matter (PM) mass. For example, combustion systems emit vapors that condense onto existing particles or form new particles as the emissions are cooled and diluted. Upon entering the atmosphere, emissions are exposed to atmospheric oxidants and sunlight, which causes them to evolve chemically and physically, generating secondary PM. This review discusses these transformations, focusing on organic PM. Organic PM emissions are semi -volatile at atmospheric conditions and thus their partitioning varies continuously with changing temperature and concentration. Because organics contribute a large portion of the PM mass emitted by most combustion sources, these emissions cannot be represented using a traditional, static emission factor. Instead, knowledge of the volatility distribution of emissions is required to explicitly account for changes in gas-particle partitioning. This requires updating how PM emissions from combustion systems are measured and simulated from combustion systems. Secondary PM production often greatly exceeds the direct or primary PM emissions; therefore, secondary PM must be included in any assessment of the contribution of combustion systems to ambient PM concentrations. Low-volatility organic vapors emitted by combustion systems appear to be very important secondary PM precursors that are poorly accounted for in inventories and models. The review concludes by discussing the implications that the dynamic nature of these PM emissions have on source testing for emission inventory development and regulatory purposes. This discussion highlights important linkages between primary and secondary PM, which could lead to simplified certification test procedures while capturing the emission components that contribute most to atmospheric PM mass.

Synthesis of the Southeast Atmosphere Studies: Investigating Fundamental Atmospheric Chemistry Questions

AbstractThe Southeast Atmosphere Studies (SAS), which included the Southern Oxidant and Aerosol Study (SOAS); the Southeast Nexus (SENEX) study; and the Nitrogen, Oxidants, Mercury and Aerosols: Distributions, Sources and Sinks (NOMADSS) study, was deployed in the field from 1 June to 15 July 2013 in the central and eastern United States, and it overlapped with and was complemented by the Studies of Emissions, Atmospheric Composition, Clouds and Climate Coupling by Regional Surveys (SEAC4RS) campaign. SAS investigated atmospheric chemistry and the associated air quality and climate-relevant particle properties. Coordinated measurements from six ground sites, four aircraft, tall towers, balloon-borne sondes, existing surface networks, and satellites provide in situ and remotely sensed data on trace-gas composition, aerosol physicochemical properties, and local and synoptic meteorology. Selected SAS findings indicate 1) dramatically reduced NOx concentrations have altered ozone production regimes; 2) indica...