Hygroscopicity of ambient submicron particles in urban Hangzhou, China

Abstract

In this study, hygroscopicity of size-segregated ambient submicron particles in urban Hangzhou was studied from 28th December 2009 to 18th January 2010, using a hygroscopicity-tandem differential mobility analyzer (H-TDMA). The submicron particles in Hangzhou showed a minor hygroscopic growth at 73% relative humidity (RH), and then grew significantly between 77% and 82% RH. Monomodal distribution accounted for 90% for 30 nm particles, 17% for 50 nm particles, and less than 7% for particles larger than 50 nm at 82% RH. Deconvolution of the bimodal distribution indicated a less hygroscopic group and a more hygroscopic group, with the fraction of the more hygroscopic group increasing with the initial dry particle size and then remaining almost constant for accumulation mode particles. Our results imply that submicron particles in urban Hangzhou were almost entirely externally mixed, and the hygroscopic properties of ambient particles in urban Hangzhou were mainly a function of their size and chemical composition.

An analysis of diurnal cycles in the mass of ambient aerosols derived from biomass burning and agro‐industry

“…[40] A final consideration is that the hygroscopic behavior of particles of mixed composition, containing inorganic species together with soluble organic compounds, can differ from that of single-component aerosols. There is no clear consensus in the literature, with both increases and decreases in DRH values having been reported for mixed aerosols, compared to those containing inorganic substances alone [Choi and Chan, 2002;Miñambres et al, 2010;Wu et al, 2011;Zhang et al, 2011]. The chemical measurements (Table 2) showed that WSOC contributed 66.5%, on average, to the total mass of the soluble aerosol species measured, so that the existence of internal mixtures of inorganic compounds and WSOC could potentially affect aerosol growth rates.…”

Tropospheric aerosol hygroscopicity in China

“…Bimodal hygroscopicity distribution was observed for 50-200 nm aerosols, while unimodal hygroscopicity distribution was observed for 30 nm aerosols (Zhang et al, 2011). The average κ values decreased from 0.121 at 30 nm to 0.065 at 80 nm for the low hygroscopic mode, and a further increase in particle size (up to 200 nm) did not lead to significant change in κ values (Zhang et al, 2011). For comparison, the average κ values increased from 0.303 at 30 nm to 0.343 at 80 nm for the more hygroscopic mode, and a further increase in particle size only resulted in a very small increase in κ values.…”

“…For comparison, the average κ values increased from 0.303 at 30 nm to 0.343 at 80 nm for the more hygroscopic mode, and a further increase in particle size only resulted in a very small increase in κ values. In addition, number fractions of particles in the more hygroscopic mode increased from ∼ 48 % for 30 nm to ∼ 70 % for 100 nm and remained nearly constant for 100-200 nm (Zhang et al, 2011).…”

“…Up to now, only one aerosol hygroscopic growth study was carried out in Hangzhou, at the ZJU site located on the Huajiachi campus of Zhejiang University (30 • 16 N, 120 • 11 E). Aerosol hygroscopic growth was measured at 70 %-90 % RH (mainly at 82 %) in December 2009-January 2010 (Zhang et al, 2011). Bimodal hygroscopicity distribution was observed for 50-200 nm aerosols, while unimodal hygroscopicity distribution was observed for 30 nm aerosols (Zhang et al, 2011).…”

“…Aerosol hygroscopic growth was measured at 70 %-90 % RH (mainly at 82 %) in December 2009-January 2010 (Zhang et al, 2011). Bimodal hygroscopicity distribution was observed for 50-200 nm aerosols, while unimodal hygroscopicity distribution was observed for 30 nm aerosols (Zhang et al, 2011). The average κ values decreased from 0.121 at 30 nm to 0.065 at 80 nm for the low hygroscopic mode, and a further increase in particle size (up to 200 nm) did not lead to significant change in κ values (Zhang et al, 2011).…”