Distinct diurnal variation in organic aerosol hygroscopicity and its relationship with oxygenated organic aerosol

Abstract

Abstract. The hygroscopicity of organic aerosol (OA) is important for investigation of its climatic and environmental impacts. However, the hygroscopicity parameter κOA remains poorly characterized, especially in the relatively polluted environment on the North China Plain (NCP). Here we conducted simultaneous wintertime measurements of bulk aerosol chemical compositions of PM2.5 and PM1 and bulk aerosol hygroscopicity of PM10 and PM1 on the NCP using a capture-vaporizer time-of-flight aerosol chemical speciation monitor (CV-ToF-ACSM) and a humidified nephelometer system which measures the aerosol light-scattering enhancement factor f(RH). A method for calculating κOA based on f(RH) and bulk aerosol chemical-composition measurements was developed. We found that κOA varied in a wide range with significant diurnal variations. The derived κOA ranged from almost 0.0 to 0.25, with an average (±1σ) of 0.08 (±0.06) for the entire study. The derived κOA was highly correlated with f44 (fraction of m∕z 44 in OA measured by CV-ToF-ACSM), an indicator of the oxidation degree of OA (R=0.79), and the relationship can be parameterized as κOA=1.04×f44-0.02 (κOA=0.3×O:C-0.02, based on the relationship between the f44 and O∕C ratio for CV-ToF-ACSM). On average, κOA reached the minimum (0.02) in the morning near 07:30 local time (LT) and then increased rapidly, reaching the peak value of 0.16 near 14:30 LT. The diurnal variations in κOA were highly and positively correlated with those of mass fractions of oxygenated OA (R=0.95), indicating that photochemical processing played a dominant role in the increase in κOA in winter on the NCP. Results in this study demonstrate the potential wide applications of a humidified nephelometer system together with aerosol composition measurements for investigating the hygroscopicity of OA in various environments and highlight that the parameterization of κOA as a function of OA aging processes needs to be considered in chemical transport models for better evaluating the impacts of OA on cloud formation, atmospheric chemistry, and radiative forcing.

Mass spectral characterization of primary emissions and implications in source apportionment of organic aerosol

“…One explanation is that f 60 depends on biomass fuels, burning conditions (e.g., flaming or smoldering), and also chemical aging (Hennigan et al, 2011;Schneider et al, 2006;Collier et al, 2016). In addition, we also observed relatively high fractions of C x H y N + z in BBOA (4.2 %-10.2 %) and high N/C ratios (0.014-0.039), consistent with the observations of abundant nitrogen-containing organic compounds, e.g., N-heterocyclic alkaloid compounds, amines, and nitrated phenols from biomass burning (Reyes-Villegas et al, 2018b;Bottenus et al, 2018;Wang et al, 2017;Laskin et al, 2009;Desyaterik et al, 2013). Compared with SV-AMS, the BBOA spectra of CV-ACSM are overall similar (R 2 = 0.93-0.96, Fig.…”

Characteristics, primary sources and secondary formation of water-soluble organic aerosols in downtown Beijing

“…The correlation pattern of another monoterpene SOA tracer, cis-pinonic acid, was different from that of 3-hydroxyglutaric acid. Chamber studies showed that cis-pinonic acid could be produced through gas-phase reactions of monoterpenes (Yu et al, 1999;Larsen et al, 2001), which significantly contributed to the newly nucleated particles (Zhang et al, 2012). Previous field observations also found that cis-pinonic acid was closely associated with the nucleation processes in the first step of the SOA formation from organic vapors (Alier et al 2013;van Drooge et al, 2018).…”

Tropospheric aerosol hygroscopicity in China

“…A variety of instruments have been developed to measure CCN number concentrations (Twomey, 1963;Sinnarwalla and Alofs, 1973;Fukuta and Saxena, 1979;Hudson, 1989;Ji et al, 1998;Chuang et al, 2000;McMurry, 2000;Nenes et al, 2001;Otto et al, 2002;VanReken et al, 2004;Roberts and Nenes, 2005;Frank et al, 2007;Kreidenweis and Asa-Awuku, 2014). Currently, the most widely used one is the continuous-flow streamwise thermal gradient CCN counter based on the design of Roberts and Nenes (2005) and Lance et al (2006) and commercialized by Droplet Measurement Technologies. Mode details of this instrument can be found elsewhere (Roberts and Nenes, 2005;Lance et al, 2006).…”

“…Currently, the most widely used one is the continuous-flow streamwise thermal gradient CCN counter based on the design of Roberts and Nenes (2005) and Lance et al (2006) and commercialized by Droplet Measurement Technologies. Mode details of this instrument can be found elsewhere (Roberts and Nenes, 2005;Lance et al, 2006).…”

“…Measurements of size-resolved CCN activities have been discussed in a number of previous studies (Lance et al, 2006;Frank et al, 2007;Petters et al, 2007;Rose et al, 2008;Good et al, 2010;Moore et al, 2010;Rose et al, 2010;Bougiatioti et al, 2011). In many studies, an aerosol flow sampled from the ambient air, after being dried to < 20 % RH, is passed through an aerosol neutralizer and then a DMA to produce quasi-monodisperse aerosols.…”