A statistical proxy for sulphuric acid concentration
Other literature type, Article
Smith, J. N.
McMurry, P. H.
Lehtinen, K. E. J.
Mauldin III, R. L.
(issn: 1680-7324, eissn: 1680-7324)
Gaseous sulphuric acid is a key precursor for new particle formation in the
atmosphere. Previous experimental studies have confirmed a strong
correlation between the number concentrations of freshly formed particles
and the ambient concentrations of sulphuric acid. This study evaluates a
body of experimental gas phase sulphuric acid concentrations, as measured by
Chemical Ionization Mass Spectrometry (CIMS) during six intensive
measurement campaigns and one long-term observational period. The campaign
datasets were measured in Hyytiälä, Finland, in 2003 and 2007, in
San Pietro Capofiume, Italy, in 2009, in Melpitz, Germany, in 2008, in
Atlanta, Georgia, USA, in 2002, and in Niwot Ridge, Colorado, USA, in 2007.
The long term data were obtained in Hohenpeissenberg, Germany, during 1998
to 2000. The measured time series were used to construct proximity measures
("proxies") for sulphuric acid concentration by using statistical analysis
methods. The objective of this study is to find a proxy for sulfuric acid
that is valid in as many different atmospheric environments as possible. Our
most accurate and universal formulation of the sulphuric acid concentration
proxy uses global solar radiation, SO<sub>2</sub> concentration, condensation sink
and relative humidity as predictor variables, yielding a correlation measure
(<i>R</i>) of 0.87 between observed concentration and the proxy predictions.
Interestingly, the role of the condensation sink in the proxy was only
minor, since similarly accurate proxies could be constructed with global
solar radiation and SO<sub>2</sub> concentration alone. This could be attributed
to SO<sub>2</sub> being an indicator for anthropogenic pollution, including
particulate and gaseous emissions which represent sinks for the OH radical
that, in turn, is needed for the formation of sulphuric acid.