Abstract
Abstract. Water vapor has been proposed to amplify the severe haze pollution in China by enhancing the aerosol–radiation feedback (ARF). Observations have revealed that the near-surface PM2.5 concentrations ([PM2.5]) generally exhibit an increasing trend with relative humidity (RH) in the North China Plain (NCP) during 2015 wintertime, indicating that the aerosol liquid water (ALW) caused by hygroscopic growth could play an important role in the PM2.5 formation and accumulation. Simulations during a persistent and heavy haze pollution episode from 5 December 2015 to 4 January 2016 in the NCP were conducted using the WRF-Chem Model to comprehensively quantify contributions of the ALW effect to near-surface [PM2.5]. The WRF-Chem Model generally performs reasonably well in simulating the temporal variations in RH against measurements in the NCP. The factor separation approach (FSA) was used to evaluate the contribution of the ALW effect on the ARF, photochemistry, and heterogeneous reactions to [PM2.5]. The ALW not only augments particle sizes to enhance aerosol backward scattering but also increases the effective radius to favor aerosol forward scattering. The contribution of the ALW effect on the ARF and photochemistry to near-surface [PM2.5] is not significant, being generally within 1.0 µg m−3 on average in the NCP during the episode. Serving as an excellent substrate for heterogeneous reactions, the ALW substantially enhances the secondary aerosol (SA) formation, with an average contribution of 71 %, 10 %, 26 %, and 48 % to near-surface sulfate, nitrate, ammonium, and secondary organic aerosol concentrations. Nevertheless, the SA enhancement due to the ALW decreases the aerosol optical depth and increases the effective radius to weaken the ARF, reducing near-surface primary aerosols. The contribution of the ALW total effect to near-surface [PM2.5] is 17.5 % on average, which is overwhelmingly dominated by enhanced SA. Model sensitivities also show that when the RH is less than 80 %, the ALW progressively increases near-surface [PM2.5] but commences to decrease when the RH exceeds 80 % due to the high occurrence frequencies of precipitation.
Highlights
Atmospheric aerosols or fine particle matter (PM2.5) influences the climate directly by scattering and absorbing the solar radiation and indirectly by serving as cloud condensation nuclei and ice nuclei
The attenuation of incoming solar radiation caused by the aerosol liquid water (ALW) decreases the photolysis rates, being unfavorable for photochemical activities and lowering the atmospheric oxidation capability (AOC)
Field measurements show that a large fraction of secondary aerosols (SA) in PM2.5 has been observed in the North China Plain (NCP) during wintertime (Sun et al, 2013; Guo et al, 2014; Xu et al, 2015)
Summary
Atmospheric aerosols or fine particle matter (PM2.5) influences the climate directly by scattering and absorbing the solar radiation and indirectly by serving as cloud condensation nuclei and ice nuclei High levels of PM2.5 in the atmosphere cause severe haze pollution, impairing visibility and exerting deleterious effects on the ecological system and human health (Chan and Yao, 2008; Zhang et al, 2013; Kurokawa et al, 2013; Weinhold, 2008; Parrish and Zhu, 2009). In addition to anthropogenic emissions, the poor air quality is generally influenced by stagnant meteorological situations with weak winds and high relative humidity RH, as an important meteorological factor in the atmosphere, considerably affects the formation, chemical composition, and physical properties of atmospheric aerosols (Seinfeld et al, 2001; Hallquist et al, 2009; Poulain et al, 2010; Nguyen et al, 2011)
Sign-in/Register to view highlights & summary Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
