Abstract
Biomass-burning (BB) aerosols, acting as cloud condensation nuclei (CCN), can influence cloud microphysical and radiative properties. In this study, we present CCN measured near the BB source regions over northern Southeast Asia (Doi Ang Khang, Thailand) and at downwind receptor areas (Lulin Atmospheric Background Station, Taiwan), focusing exclusively on 13–20 March 2013 as part of 2013 spring campaign of the Seven SouthEast Asian Studies (7-SEAS) intensive observation. One of the campaign’s objectives is to characterize BB aerosols serving as CCN in SouthEast Asia (SEA). CCN concentrations were measured by a CCN counter at 5 supersaturation (SS) levels: 0.15%, 0.30%, 0.45%, 0.60%, and 0.75%. In addition, PM2.5 and black carbon mass concentrations were analyzed by using a tapered element oscillating microbalance and an aethalometer. It was found the number-size distributions and the characteristics of hygroscopicity (e.g., activation ratio and κ) of BB aerosols in SEA have a strong diurnal pattern, and different behaviors of patterns were characterized under two distinct weather systems. The overall average κ value was low (0.05–0.1) but comparable with previous CCN studies in other BB source regions. Furthermore, a large fraction of UV-absorbing organic material (UVBC) and high Delta-C among BB aerosols were also observed, which suggest the existence of substantial particulate organic matter in fresh BB aerosols. These data provide the most extensive characterization of BB aerosols in SEA until now.
Highlights
Biomass-burning (BB) activity is a major contributor to global fine particles and particle precursors (Crutzen and Andreae, 1990; Andreae et al, 2004; Aiken et al, 2010)
We present cloud condensation nuclei (CCN) measured near the BB source regions over northern Southeast Asia (Doi Ang Khang, Thailand) and at downwind receptor areas (Lulin Atmospheric Background Station, Taiwan), focusing exclusively on 13–20 March 2013 as part of 2013 spring campaign of the Seven SouthEast Asian Studies (7-SEAS) intensive observation
Near the BB source region, the rise of CN concentration potentially indicates the increasing of number of neighboring fire events, which is evidenced by the fire counts recorded by Terra and Aqua (Fig. S2)
Summary
Biomass-burning (BB) activity is a major contributor to global fine particles and particle precursors (Crutzen and Andreae, 1990; Andreae et al, 2004; Aiken et al, 2010). In addition to aerosol’s direct radiative effects, such as backscattering and absorption of solar radiation (Bhawar and Rahul, 2013; Wang et al, 2015; Sayer et al, 2016; Pani et al, 2016a, b), BB aerosols have indirect influence on the radiation budget and the regional water cycle by acting as cloud condensation nuclei (CCN). Model simulations have demonstrated that BB aerosols are a major global source of CCN (Pierce et al, 2007; Spracklen et al, 2011). The main parameters governing CCN activation and initial cloud droplet growth are the number, size, and hygroscopicity of aerosol particles, as well as updraft velocity at the cloud base and the resulting water vapor supersaturation (SS) (Reutter et al, 2009). The number fraction of CN activated to CCN at a specific SS (AR(SS)) is determined as: Hsiao et al, Aerosol and Air Quality Research, 16: 2742–2756, 2016
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