Abstract
Abstract. Interaction of anthropogenic particles with radiation and clouds plays an important role in Arctic climate change. The mixing state of aerosols is a key parameter to influence aerosol radiation and aerosol–cloud interactions. However, little is known of this parameter in the Arctic, preventing an accurate representation of this information in global models. Here we used transmission electron microscopy with energy-dispersive X-ray spectrometry, scanning electron microscopy, nanoscale secondary ion mass spectrometry, and atomic forces microscopy to determine the size and mixing state of individual sulfate and carbonaceous particles at 100 nm to 2 µm collected in the Svalbard Archipelago in summer. We found that 74 % by number of non-sea-salt sulfate particles were coated with organic matter (OM); 20 % of sulfate particles also had soot inclusions which only appeared in the OM coating. The OM coating is estimated to contribute 63 % of the particle volume on average. To understand how OM coating influences optical properties of sulfate particles, a Mie core–shell model was applied to calculate optical properties of individual sulfate particles. Our result shows that the absorption cross section of individual OM-coated particles significantly increased when assuming the OM coating as light-absorbing brown carbon. Microscopic observations here suggest that OM modulates the mixing structure of fine Arctic sulfate particles, which may determine their hygroscopicity and optical properties.
Highlights
Surface temperatures are rising faster in the Arctic than the rest of globe (IPCC, 2013)
OM can be divided into primary organic matter (POM) and secondary organic matter (SOM)
SOM is produced from the chemical oxidation of volatile organic compounds (VOCs) and often exhibits OM coating on S-rich particles (Li et al, 2016; Moffet et al, 2013; Riemer et al, 2019)
Summary
Surface temperatures are rising faster in the Arctic than the rest of globe (IPCC, 2013). Increased humaninduced emissions of long-lived greenhouse gases are certainly one of the driving factors, air pollutants, such as aerosols and ozone, are important contributors to climate change in the Arctic (Law and Stohl, 2007; Shindell, 2007). H. Yu et al.: Organic coatings on secondary sulfate particles al., 2013). Yu et al.: Organic coatings on secondary sulfate particles al., 2013) These studies show that regional pollutants and local natural aerosol production affect sea ice albedo and the heat balance of the atmosphere, especially in the summer when mid-latitude transport is not as frequent relative to that during the winter–spring Arctic Haze season (Hansen and Nazarenko, 2004; Jacob et al, 2010; Shindell, 2007)
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