Significant contribution of organics to aerosol liquid water content in winter in Beijing, China

Abstract

Abstract. The aerosol liquid water (ALW) content (ALWC), an important component of atmospheric particles, has a significant effect on atmospheric optical properties, visibility and multiphase chemical reactions. In this study, ALWC is determined from aerosol hygroscopic growth factor (GF) and particle number size distribution (PNSD) measurements and is also simulated by ISORROPIA II, a thermodynamic equilibrium model, with measured aerosol chemical composition data taken at an urban site in Beijing from 8 November to 15 December 2017. Rich measurements made during the experiment concerning virtually all aerosol properties allow us not only to derive the ALWC but also to study the contributions by various species for which little has been done in this region. The simulated ALWC including the contribution of organics and the calculated ALWC are highly correlated (coefficient of determination R2=0.92). The ALWC contributed by organics (ALWCOrg) accounts for 30 %±22 % of the total ALWC during the sampling period. These results suggest a significant contribution of organics to ALWC, which is rather different from previous studies that showed negligible contributions by organics. Our results also show that ALWC correlates well with the mass concentrations of sulfate, nitrate, and secondary organic aerosols (SOAs) (R2=0.66, 0.56 and 0.60, respectively). We further noted that accumulation mode particles play a key role in determining ALWC, dominating among all the aerosol modes. ALWC is an exponential function of ambient relative humidity (RH), whose strong diurnal variation influence the diurnal variation of ALWC. However, there is a 3 h lag between the extremes of ALWC and RH values, due to the diurnal variations in PNSD and aerosol chemical composition. Finally, a case study reveals that ALWCOrg plays an important role in the formation of secondary aerosols through multiphase reactions at the initial stage of a heavy-haze episode.

Improved 1 km resolution PM<sub>2.5</sub> estimates across China using enhanced space–time extremely randomized trees

“…Most meteorological variables contribute more to PM 2.5 estimates, especially BLH, ET and TEM, with average importance scores of 9.6 %, 7.7 % and 7.3 %, respectively. The PM 2.5 -AOD relationship might largely depend on the compositions (e.g., aerosol water; Reddington et al, 2019;Jin et al, 2020). High RH conditions and precipitation should have large influences on the production and removal of PM 2.5 (Sun et al, 2014;Zheng et al, 2015).…”

“…Numerous studies have illustrated that high PM 2.5 concentrations adversely affect human health (Peng et al, 2009;Bartell et al, 2013;Chowdhury and Dey, 2016;Crippa et al, 2019;Song et al, 2019), severely impair the atmospheric environment (Z. Li et al, 2017), and significantly influence cloud and precipitation systems through aerosol radiative and microphysical effects (Koren et al, 2014;Seinfeld et al, 2016). Silva et al (2013) showed that about 2.1 million people have died each year, resulting from increasing PM 2.5 concentrations around the world.…”

Importance of gas-particle partitioning of ammonia in haze formation in the rural agricultural environment

“…NH 3 emission sources include agricultural practices, onroad vehicles (Chang et al, 2016;Sun et al, 2017), and biomass burning (Lamarque et al, 2010;Paulot et al, 2017). Recent field measurements and modeling work reveal that agricultural practices (i.e., animal manure and fertilizer application) contribute to 80 %-90 % of total NH 3 emissions in China (Zhang et al, 2018;Kang et al, 2016;Huang et al, 2011). Globally, NH 3 emissions are projected to continue to rise along with an increasing demand in chemical fertilizers due to the growing human population (Erisman et al, 2008;Stewart et al, 2005) and in part because limiting NH 3 emissions has not been targeted as a priority in most countries.…”

Hygroscopicity of Different Types of Aerosol Particles: Case Studies Using Multi-Instrument Data in Megacity Beijing, China

“…Understanding the mechanism of changes in aerosol characteristics in the atmosphere is of great significance for studying their effects on the Earth's climate and its changes. A key factor influencing aerosol properties is water vapor, which may be uptaken by aerosol particles [4,5] to alter their optical and microphysical properties, especially scattering and absorption [6].…”