AAAR 33rd Annual Conference
October 20 - October 24, 2014
Rosen Shingle Creek
Orlando, Florida, USA
Abstract View
Reactions Between Water-Soluble Organic Acids and Nitrates in Atmospheric Aerosols: Recycling of Nitric Acid and Formation of Organic Salts
BINGBING WANG, Alexander Laskin, Pacific Northwest National Laboratory
Abstract Number: 119 Working Group: Aerosol Chemistry
Abstract Atmospheric aerosol particles often include a complex mixture of inorganic and organic materials. Nitrate as an important inorganic component can be chemically formed in the atmosphere. For example, formation of sodium nitrate (NaNO$_3) and calcium nitrate (Ca(NO$_3)$_2) occurs when nitrogen oxides and nitric acid (HNO$_3) react with sea salt and calcite, respectively. Organic acids contribute a significant fraction of photochemically formed secondary organics that can condense on the preexisting particles. We present here a systematic microanalysis study on chemical composition of laboratory-generated particles composed of water soluble organic acids and nitrates (NaNO$_3 and Ca(NO$_3)$_2) using elemental X-ray analysis and fourier transform infrared micro-spectroscopy analysis. Results show that water soluble organic acids can react with nitrates and release gaseous HNO$_3 during the dehydration process. These reactions are attributed to acid displacement of nitrate with weak organic acids driven by the evaporation of HNO$_3 into gas phase because of its relatively high volatility. The reactions result in significant nitrate depletion and formation of organic salts in mixed organic acids/nitrate particles that, in turn, may affect their physical and chemical properties relevant to atmospheric environment and climate. The results indicate a potential mechanism of HNO$_3 recycling that may further affect atmospheric chemistry.