Enhancement of PM_2.5 Concentrations by Aerosol‐Meteorology Interactions Over China

Abstract

Aerosol‐meteorology interactions can change surface aerosol concentrations via different mechanisms such as altering radiation budget or cloud microphysics. However, few studies investigated the impacts of different mechanisms on temporal and spatial distribution of PM2.5 concentrations over China. Here we used the fully coupled Weather Research and Forecasting model with online chemistry (WRF‐Chem) to quantify the enhancement of PM2.5 concentrations by aerosol‐meteorology feedback in China in 2014 for different seasons and separate the relative impacts of aerosol radiation interactions (ARIs) and aerosol‐cloud interactions (ACIs). We found that ARIs and ACIs could increase population‐weighted annual mean PM2.5 concentration over China by 4.0 μg/m3 and 1.6 μg/m3, respectively. We found that ARIs play a dominant role in aerosol‐meteorology interactions in winter, while the enhancement of PM2.5 concentration by ARIs and ACIs is comparable in other three seasons. ARIs reduced the wintertime monthly mean wind speed and planetary boundary layer (PBL) height by up to 0.1 m/s and 160 m, respectively, but increased the relative humidity by up to 4%, leading to accumulation of pollutants within PBL. Also, ARIs reduced dry deposition velocity of aerosols by up to 20%, resulting in an increase in PM2.5 lifetime and concentrations. ARIs can increase wintertime monthly mean surface PM2.5 concentration by a maximum of 30 μg/m3 in Sichuan Basin. ACIs can also increase PM2.5 concentration with more significant impacts in wet seasons via reduced wet scavenging and enhanced in‐cloud chemistry. Dominant processes in PM2.5 enhancement are also clarified in different seasons. Results show that physical process is more important than chemical processes in winter in ARIs, while chemical process of secondary inorganic aerosols production may be crucial in wet seasons via ACIs.

The impact of aerosol–radiation interactions on the effectiveness of emission control measures

“…The Morrison microphysics scheme simulates ACI via linking prognostic aerosols to cloud condensation nuclei. We use a prescribed cloud droplet number concentration (CDNC) of 10 cm −3 in the Morrison microphysics scheme to exclude ACI as well as anthropogenic impacts on clouds (Zhao et al 2017, Zhang et al 2018. Although the CDNC value of 10 cm −3 does not represent the BTH condition, sensitivity simulations with CDNC of 200 cm −3 as will be discussed below show minor changes on our results.…”

“…Here we use the coupled meteorology-chemistry model WRF-Chem to address this issue. A recent WRF-Chem modeling study has found that the ACI effects are much smaller than ARI over the BTH region in fall and winter (Zhang et al 2018), when severe haze episodes occur frequently. Besides, ACI effects are highly uncertain in current models (Boucher et al 2013).…”

“…Previous studies have shown that aerosolmeteorology interactions can strongly impact PM 2.5 concentrations during pollution episodes (Wang et al 2014) as well as for monthly averages (Zhao et al 2017, Zhang et al 2018. One question remaining largely unexplored is that how these interactions would respond to temporary emission control measures.…”

Air quality and climate change, Topic 3 of the Model Inter-Comparison Study for Asia Phase III (MICS-Asia III) – Part 2: aerosol radiative effects and aerosol feedbacks

“…Studies examining how aerosols interact with weather and climate remain uncertain and limited. Recently, with the rapid development of coupled meteorology and chemistry models, many new studies have been conducted to investigate the aerosol direct and indirect effects and feedbacks (Baklanov et al, 2017;Forkel et al, 2015;Gao et al, 2016Gao et al, , 2017Grell et al, 2005;Han, 2010;Huang et al, 2016;Jacobson et al, 2007;Saide et al, 2012;Yang et al, 2011;Zhang et al, 2010). In highly polluted regions like Asia, aerosol feedbacks can be particularly important (Gao et al, 2016(Gao et al, , 2017.…”

The Impact of the Aerosol Direct Radiative Forcing on Deep Convection and Air Quality in the Pearl River Delta Region

“…Moreover, the aerosol‐meteorology interactions can in turn change surface aerosol concentrations. Recent studies reveal that both aerosol‐radiation and aerosol‐cloud interactions increase surface aerosol concentration (Wang, Wang, et al, ; Zhang et al, , ). Nevertheless, the underlying mechanism is rarely discussed in the PRD region and needs to be further investigated.…”