Size‐segregated measurements of cloud condensation nucleus activity and hygroscopic growth for aerosols at Cape Hedo, Japan, in spring 2008

Abstract

[1] Size-segregated measurements of cloud condensation nucleus (CCN) activity and hygroscopic growth were performed simultaneously for sulfate-rich aerosols at Cape Hedo, Okinawa, Japan, in spring 2008. The CCN fractions as functions of particle size at water vapor supersaturations of 0.44%, 0.25%, and 0.10% had nearly stepwise increases, and the diameters for 50% activation of its maximum (d act ) were close to that of (NH 4 ) 2 SO 4 . The size-resolved hygroscopic growth factor g measured using a hygroscopicity tandem differential mobility analyzer at 85% relative humidity (RH) mainly showed unimodal and highly hygroscopic characteristics. The observed characteristics as well as aerosol mass spectrometer data suggest the dominance of internally mixed ammoniated sulfate-rich particles. A clear negative correlation between d act and median g (g median ) was observed for Aitken-mode particles, and backward air mass trajectories indicate lower d act and higher g of the aerosols from China and the Pacific and the opposite tendency for those from Korea and Japan. The size dependence of g median suggests that less hygroscopic carbonaceous components were more enriched in Aitkenmode particles and therefore affect the CCN activity and hygroscopicity. The CCN activation diameters were predicted on the basis of g median using a core-shell model. The modeled activation diameters reasonably agreed with measured d act , suggesting that the surface tension lowering effect due to organics and the enhancement of bulk hygroscopicity at high RH due to sparingly soluble or polymeric compounds were small. The results suggest that CCN activity of sulfate-rich aerosol particles is predicted well in regional and global aerosol models without incorporating these effects.

Simultaneous Measurement of CCN Activity and Chemical Composition of Fine-Mode Aerosols at Noto Peninsula, Japan, in Autumn 2012

“…The mean organic mass fraction of 0.49 was larger than that of Jeju Island (0.41; Topping et al, 2004), Okinawa Island (0.17 to 0.20;Takami et al, 2007;Miyoshi et al, 2013). This result is consistent with the smaller κ values as compared to those of Jeju Island and Okinawa Island (Mochida et al, 2010). The mean organic mass fraction was comparable with that for Fukue Island (0.45; Takami et al, 2005).…”

“…However, the κ CCN values were clearly smaller than those of previous studies in East Asia. The previously reported values such as 0.49 ± 0.09 for Jeju Island, Korea and 0.50 ± 0.05 for Okinawa Island, Japan (Mochida et al, 2010) were closer to the value of κ of pure (NH 4 ) 2 SO 4 (0.61; Petters and Kreidenweis, 2007). Note that κ CCN values at other sites were calculated by the same method as used in this study, using the CCN activation diameter reported in the literature Mochida et al, 2010).…”

“…Thus, simultaneous measurement of sizesegregated CCN activity and chemical composition of the ambient aerosols under controlled SS conditions is an effective method for better characterizing CCN activity of the ambient aerosols (e.g., Gunthe et al, 2009;Mochida et al, 2010;Rose et al, 2010).…”

“…The pollutants are transported by the prevailing wind (mainly westward or northwest-ward) as the "Asian outflow", and may impact the regional climate. To investigate the characteristics of CCN properties or chemical compositions of fine-mode aerosols in the Asian outflow, several observations have been conducted in remote monitoring sites in East Asia such as Jeju Island, Korea (e.g., Topping et al, 2004;, Okinawa Island, Japan (e.g., Takami et al, 2007;Mochida et al, 2010) and Fukue Island, Japan (e.g., Takami et al, 2005). Indeed, these remote super-sites are well located for characterizing the Asian outflow directly downwind of central or south China where industrial activity is particularly concentrated (Fig.…”

Assessment of cloud condensation nucleus activation of urban aerosol particles with different hygroscopicity and the application to the cloud parcel model

“…Hereafter, the CCNC-derived d act and σ are expressed as d act , CCN and σ CCN , respectively. The SS in the CCNC was calculated to be 0.18%, 0.49%, and 0.95% from d act,CCN of ammonium sulfate particles, using the Köhler equation and incorporating the Pitzer model as described by Mochida et al [2010].…”