Analysis of meteorology–chemistry interactions during air pollution episodes using online coupled models within AQMEII phase-2

Abstract

This study reviews the top ranked meteorology and chemistry interactions in online coupled models recommended by an experts' survey conducted in COST Action EuMetChem and examines the sensitivity of those interactions during two pollution episodes: the Russian forest fires 25 Jul–15 Aug 2010 and a Saharan dust transport event from 1 Oct to 31 Oct 2010 as a part of the AQMEII phase-2 exercise. Three WRF-Chem model simulations were performed for the forest fire case for a baseline without any aerosol feedback on meteorology, a simulation with aerosol direct effects only and a simulation including both direct and indirect effects. For the dust case study, eight WRF-Chem and one WRF-CMAQ simulations were selected from the set of simulations conducted in the framework of AQMEII. Of these two simulations considered no feedbacks, two included direct effects only and five simulations included both direct and indirect effects. The results from both episodes demonstrate that it is important to include the meteorology and chemistry interactions in online-coupled models. Model evaluations using routine observations collected in AQMEII phase-2 and observations from a station in Moscow show that for the fire case the simulation including only aerosol direct effects has better performance than the simulations with no aerosol feedbacks or including both direct and indirect effects. The normalized mean biases are significantly reduced by 10–20% for PM10 when including aerosol direct effects. The analysis for the dust case confirms that models perform better when including aerosol direct effects, but worse when including both aerosol direct and indirect effects, which suggests that the representation of aerosol indirect effects needs to be improved in the model

Simulating aerosol–radiation–cloud feedbacks on meteorology and air quality over eastern China under severe haze conditionsin winter

“…Several studies under the Air Quality Model Evaluation International Initiative (AQMEII) project suggested that the aerosol indirect effect dominated in aerosol feedbacks on solar radiation, temperature, and PBL height (Forkel et al, 2012Kong et al, 2014;Makar et al, 2014a). Different from these studies, we find that aerosol indirect effects have little influence on the downward shortwave flux at the ground, 2 m temperature, 10 m wind speed, and PBL height (not shown here).…”

Sensitivity of feedback effects in CBMZ/MOSAIC chemical mechanism

“…Also we found similar values of cloud fraction, 93% in case of NONFBITand 90% for FBES3. This strong decrease of the cloud liquid water content and the associated increase in global radiation can be observed for WRF-Chem not only for the MOSAIC aerosol module but also when the MADE/SORGAM aerosol module , Kong et al, 2015 as it results mainly from the definition of the baseline conditions.…”

Impacts of aerosol-radiation feedback on local air quality during a severe haze episode in Nanjing megacity, eastern China

“…Forkel et al (2015) performed several simulations with different aerosol feedbacks for a Russian wildfire episode; they found that the inclusion of aerosol-cloud interactions led to lower cloud droplet number and higher downward solar radiation by almost 50% for regions with low aerosol concentrations. But Kong et al (2015) pointed out that the representation of aerosol indirect effects is incomplete in current models and needs to be further improved. In the future work, both the direct and indirect aerosol radiative forcing should, therefore, be taken into account when assessing the aerosol effects on atmospheric chemistry.…”

“…Since then, numerous new generations of on-line-coupled models have been developed worldwide, such as Multiscale Climate Chemistry Model (MCCM) (Grell et al, 2000), Weather Research and Forecasting-Chemistry (WRF-Chem) (Grell et al, 2005) and Global Environmental Multi-scale-Modeling Air quality and CHemistry (GEM-MACH) (Moran et al, 2010). These models have been widely used for Europe and North America and they found that the interactions between meteorology and chemistry can be significant during strong air pollution episodes (Grell et al, 2011;Konovalov et al, 2011;Wong et al, 2012;Chen et al, 2014;Kong et al, 2015;Liu et al, 2016).…”

“…However, the neglect of aerosol-chemistry feedbacks in off-line models is expected to cause noticeable biases in both meteorological and chemical forecasts (Jacobson, 1997;Wong et al, 2012;Kong et al, 2015;Makar, Gong, Milbrandt et al, 2015). Jacobson (1997) was first to develop a fully-coupled on-line model to account for the radiation feedback of size-resolved aerosols on photolysis and temperature profiles.…”