Water uptake by fresh Indonesian peat burning particles is limited by water-soluble organic matter

Abstract

Abstract. The relationship between hygroscopic properties and chemical characteristics of Indonesian biomass burning (BB) particles, which are dominantly generated from peatland fires, was investigated using a humidified tandem differential mobility analyzer. In addition to peat, acacia (a popular species at plantation) and fern (a pioneering species after disturbance by fire) were used for experiments. Fresh Indonesian peat burning particles are almost non-hygroscopic (mean hygroscopicity parameter, κ < 0.06) due to predominant contribution of water-insoluble organics. The range of κ spans from 0.02 to 0.04 (dry diameter = 100 nm, hereinafter) for Riau peat burning particles, while that for Central Kalimantan ranges from 0.05 to 0.06. Fern combustion particles are more hygroscopic (κ = 0.08), whereas the acacia burning particles have a mediate κ value (0.04). These results suggest that κ is significantly dependent on biomass types. This variance in κ is partially determined by fractions of water-soluble organic carbon (WSOC), as demonstrated by a correlation analysis (R = 0.65). κ of water-soluble organic matter is also quantified, incorporating the 1-octanolwater partitioning method. κ values for the water extracts are high, especially for peat burning particles (A 0 (a whole part of the water-soluble fraction): κ = 0.18, A 1 (highly watersoluble fraction): κ = 0.30). This result stresses the importance of both the WSOC fraction and κ of the water-soluble fraction in determining the hygroscopicity of organic aerosol particles. Values of κ correlate positively (R = 0.89) with the fraction of m/z 44 ion signal quantified using a mass spectrometric technique, demonstrating the importance of highly oxygenated organic compounds to the water uptake by Indonesian BB particles. These results provide an experimentally validated reference for hygroscopicity of organicsdominated particles, thus contributing to more accurate estimation of environmental and climatic impacts driven by Indonesian BB particles on both regional and global scales.

Secondary aerosol formation promotes water uptake by organic-rich wildfire haze particles in equatorial Asia

“…S2, demonstrating the validity of our instrument. Further details about the HTDMA are available in Chen et al (2017).…”

“…Hydrocarbon (-like) OA is known to be almost non-hygroscopic, leading to the estimation that the κ value of HOA is 0 (Gysel et al, 2007;Gunthe et al, 2009;Chang et al, 2010). Water uptake by freshly emitted biomass burning particles is generally limited, especially compared with OOA Chang et al, 2010;Chen et al, 2017). Based on our previously measured κ results of fresh Indonesian peatland burning particles, an overall mean value of κ PBOA = 0.04 was used for the fresh PBOA factor, and κ BBOA = 0.06 was applied for the non-peat BBOA factor with mixed vegetation burning mainly of acacia and fern species .…”

“…On one hand, laboratory studies have demonstrated that fresh Indonesian peat burning particles are weakly hygroscopic and almost inactive as cloud condensation nuclei (CCN) (Chand et al, 2005;Dusek et al, 2005;Chen et al, 2017). On the other hand, a field observation showed that the wildfire haze particles were highly hygroscopic during the 1997 Indonesian peatland fires (Gras et al, 1999).…”

“…The high sensitivity to organic fractions has been observed, as inorganic species are much more hygroscopic than most organic compounds. However, the roles of inorganic and organic species in water uptake by Indonesian peatland burning particles have rarely been investigated (Dusek et al, 2005;Chen et al, 2017).…”

“…Such cases have been frequently observed in particles emitted from wildfires (Petters et al, 2009;Cubison et al, 2011;Hallar et al, 2013;. Both theoretical and experimental studies demonstrated that water-soluble organic matter (WSOM) plays the key role in determining the water uptake by organic compounds (Peng et al, 2001;Gysel et al, 2004;Petters and Kreidenweis, 2007;Carrico et al, 2008;Petters et al, 2009;Lathem et al, 2013;Chen et al, 2017). For instance, freshly emitted peat burning particles are known to contain a small fraction of WSOM, which explains their limited hygroscopicity .…”