Abstract

Abstract. A new condensed toluene mechanism is incorporated into the Community Multiscale Air Quality Modeling system. Model simulations are performed using the CB05 chemical mechanism containing the existing (base) and the new toluene mechanism for the western and eastern US for a summer month. With current estimates of tropospheric emission burden, the new toluene mechanism increases monthly mean daily maximum 8-h ozone by 1.0–3.0 ppbv in Los Angeles, Portland, Seattle, Chicago, Cleveland, northeastern US, and Detroit compared to that with the base toluene chemistry. It reduces model mean bias for ozone at elevated observed ozone concentrations. While the new mechanism increases predicted ozone, it does not enhance ozone production efficiency. A sensitivity study suggests that it can further enhance ozone if elevated toluene emissions are present. While it increases in-cloud secondary organic aerosol substantially, its impact on total fine particle mass concentration is small.

Highlights

  • Toluene is an important aromatic compound that can affect ozone (O3) and secondary organic aerosol (SOA) in the atmosphere

  • Toluene chemistry in CB05 was retained from the Carbon Bond IV (CB-IV) chemical mechanism

  • This study examines the impact of the new condensed toluene mechanism on air quality model predictions in the US

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Summary

Introduction

Toluene is an important aromatic compound that can affect ozone (O3) and secondary organic aerosol (SOA) in the atmosphere. Whitten et al (2010) proposed a new condensed toluene mechanism for CB05 mechanism They performed simulations using the existing CB05 mechanism as well as the new CB05 mechanism containing the new condensed toluene mechanism for 38 environmental chamber experiments involving different combinations of toluene and oxides of nitrogen (NOx). They used four different performance metrics to compare model predictions with chamber data: maximum O3, maximum (NO-O3), NOx crossover time, and cresol concentrations (NO = nitric oxide). The new toluene mechanism provided better results than the existing toluene chemistry in simulating chamber data.

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