Abstract
Abstract. As demonstrated in a number of investigations, gaseous sulfuric acid plays a central role in atmospheric aerosol formation. Using chemical ionization mass spectrometer the gas-phase sulfuric acid and OH concentration were measured in Hyytiälä, SMEAR II station, Southern Finland during 24 March to 28 June 2007. Clear diurnal cycles were observed as well as differences between new particle formation event days and non-event days. Typically, the daily maximum concentrations of gas phase sulfuric acid varied from 3×105 to 2×106 molec cm−3 between non-event and event days. Noon-time OH concentrations varied from 3-6×105 molec cm−3 and not a clear difference between event and non-events was detected. The measured time series were also used as a foundation to develop reasonable proxies for sulfuric acid concentration. The proxies utilized source and sink terms, and the simplest proxy is radiation times sulfur dioxide divided by condensation sink. Since it is still challenging to measure sulfuric acid in ambient concentrations, and due to its significant role in atmospheric particle formation, reasonable proxies are needed. We use all together three different proxies and one chemical box model and compared their results to the measured data. The proxies for the sulfuric acid concentration worked reasonably well, and will be used to describe sulfuric acid concentrations in SMEAR II station, when no measured sulfuric acid data is available. With caution the proxies could be applied to other environments as well.
Highlights
An important phenomenon associated with the atmospheric aerosol system is the formation of new atmospheric aerosol particles
The aim of this study is to present results from a field campaign conducted in Hyytiala, Finland, and to develop physically sound proxies, and investigate their capabilities to predict ambient sulfuric acid concentrations
Higher sulfuric acid concentrations are measured during new particle formation event days since during these days clear sky prevails, which promote photochemical activity
Summary
An important phenomenon associated with the atmospheric aerosol system is the formation of new atmospheric aerosol particles. Atmospheric aerosol formation consists of a complicated set of processes that include the production of nanometer-size clusters from gaseous vapors, the growth of these clusters to detectable sizes, and their simultaneous removal by coagulation with the pre-existing aerosol particle population (Kerminen et al, 2001; Kulmala, 2003). It has been proposed, and confirmed by observations, that atmospheric new particle formation depends on the sulfuric acid concentration (Weber et al, 1996, 1997; Kulmala et al, 2006). A number of field campaigns have been performed that allow us to look at connections between the gas-phase sulfuric acid concentration and aerosol formation rate, both in laboratory and atmospheric conditions
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