Abstract
Gas- and aerosol-phase measurements of oxidants, biogenic volatile organic
compounds (BVOCs) and organic nitrates made during the Southern Oxidant and Aerosol Study (SOAS campaign, Summer 2013) in central Alabama show
that a
nitrate radical (NO3) reaction with monoterpenes leads to significant
secondary aerosol formation. Cumulative losses of NO3 to terpenes are
correlated with increase in gas- and aerosol-organic nitrate concentrations
made during the campaign. Correlation of NO3 radical consumption to
organic nitrate aerosol formation as measured by aerosol mass spectrometry and thermal dissociation laser-induced fluorescence suggests a molar yield
of aerosol-phase monoterpene nitrates of 23–44 %. Compounds observed via
chemical ionization mass spectrometry (CIMS) are correlated to predicted
nitrate loss to BVOCs and show C10H17NO5, likely a hydroperoxy
nitrate, is a major nitrate-oxidized terpene product being incorporated into
aerosols. The comparable isoprene product C5H9NO5 was observed to
contribute less than 1 % of the total organic nitrate in the aerosol phase
and correlations show that it is principally a gas-phase product from nitrate
oxidation of isoprene. Organic nitrates comprise between 30 and 45 % of the
NOy budget during SOAS. Inorganic nitrates were also monitored and
showed that during incidents of increased coarse-mode mineral dust,
HNO3 uptake produced nitrate aerosol mass loading at a rate comparable to that
of organic nitrate produced via NO3 + BVOCs.
Citation
ID:
190602
Ref Key:
ayres2015atmosphericorganic