Abstract
Abstract. While nitrate salts have critical impacts on environmental effects of atmospheric aerosols, the effects of coexisting species on hygroscopicity of nitrate salts remain uncertain. The hygroscopic behaviors of nitrate salt aerosols (NH4NO3, NaNO3, Ca(NO3)2) and their internal mixtures with water-soluble organic acids were determined using a hygroscopicity tandem differential mobility analyzer (HTDMA). The nitrate salt ∕ organic acid mixed aerosols exhibit varying phase behavior and hygroscopic growth depending upon the type of components in the particles. Whereas pure nitrate salt particles show continuous water uptake with increasing relative humidity (RH), the deliquescence transition is still observed for ammonium nitrate particles internally mixed with organic acids such as oxalic acid and succinic acid with a high deliquescence point. The hygroscopicity of submicron aerosols containing sodium nitrate and an organic acid is also characterized by continuous growth, indicating that sodium nitrate tends to exist in a liquid-like state under dry conditions. It is observed that in contrast to the pure components, the water uptake is hindered at low and moderate RH for calcium nitrate particles containing malonic acid or phthalic acid, suggesting the potential effects of mass transfer limitation in highly viscous mixed systems. Our findings improve fundamental understanding of the phase behavior and water uptake of nitrate-salt-containing aerosols in the atmospheric environment.
Highlights
Atmospheric aerosols exert significant impacts on the earth’s radiation balance by absorbing or scattering solar radiation and modifying the properties of clouds, which result in large uncertainty in climate forcing (Haywood and Boucher, 2000; Carslaw et al, 2013)
Crystalline sodium nitrate has a deliquescence point at 74.5 % RH (Tang and Munkelwitz, 1994), the prior studies found that micron and submicron NaNO3 particles formed from aqueous solutions exhibited continuous hygroscopic growth due to initial particles in a metastable or amorphous form, even at zero relative humidity (Gysel et al, 2002; Hoffman et al, 2004; Gibson et al, 2006)
Our results reveal that the nitrate salt / organic acid mixed aerosols exhibit varying phase behavior and hygroscopic growth depending upon the type of components present in the particles
Summary
Atmospheric aerosols exert significant impacts on the earth’s radiation balance by absorbing or scattering solar radiation and modifying the properties of clouds, which result in large uncertainty in climate forcing (Haywood and Boucher, 2000; Carslaw et al, 2013). Due to the considerable influence of anthropogenic sources, the major chemical form of nitrate salts in fine particulate matter is ammonium nitrate generated via the heterogeneous reaction between HNO3 and NH3 in the aerosol phase. The inorganic salts in the particle phase are generally internally mixed with organic compounds that contribute a large fraction of fine particulate matter. The hygroscopic behaviors of internally mixed aerosols composed of atmospherically relevant nitrate salts and water-soluble organic acids are determined under subsaturation conditions with a hygroscopicity tandem differential mobility analyzer (HTDMA) system. The significant effects of water-soluble organic acids with various hygroscopic characteristics on water uptake behaviors of nitrate salts have been confirmed, and relevant atmospheric implications are discussed
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
