Impact of a new condensed toluene mechanism on air quality model predictions in the US

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

Annual application and evaluation of the online coupled WRF–CMAQ system over North America under AQMEII phase 2

“…Options in WRF include the Morrison microphysics scheme (Morrison et al, 2009), version 2 of the KaineFritsch (KF2) cumulus cloud parameterization (Kain, 2004), the Asymmetric Convective Model version 2 (ACM2) for the planetary boundary layer (Pleim, 2007a, b), the Pleim-Xiu land-surface model (Xiu and Pleim, 2001), and the Rapid Radiative Transfer Model for GCMs (RRTMG) (Clough et al, 2005). Options in CMAQ include the CB05-TU chemical mechanism (Whitten et al, 2010;Sarwar et al, 2011a), the AERO6 three mode aerosol module (Appel et al, 2013; also see Simon and Bhave, 2012;Carlton et al, 2010;Foley et al, 2010;Byun and Schere, 2006;Binkowski and Roselle, 2003), wet deposition as described in Byun and Schere (2006) and dry deposition as described in Pleim and Ran (2011).…”

Extending the Community Multiscale Air Quality (CMAQ) modeling system to hemispheric scales: overview of process considerations and initial applications

“…The 2005 Carbon Bond Mechanism with updated toluene chemistry (CB05TU; Sarwar et al, 2011), commonly used in regional CMAQ applications, was also used for initial hemispheric-scale applications. Important enhancements to CB05TU were implemented to improve (1) its ability to represent multi-day chemistry associated with cycling of NO x through reservoir organic nitrate species in the mechanism and (2) representation of chemical sinks for tropospheric O 3 due to halogen-mediated chemistry in marine environments.…”

Isoprene and monoterpene emissions in south-east Australia: comparison of a multi-layer canopy model with MEGAN and with atmospheric observations

“…The chemistry scheme is the extended Carbon Bond 5 mechanism (CB05) (Sarwar et al, 2008(Sarwar et al, , 2011, consisting of 65 gas phase species, 19 aerosol species and 172 reactions. The organic species are lumped according to their carboncarbon bonding type.…”