Sulfuric acid and OH concentrations in a boreal forest site

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. The typical 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. Since it is still challenging to measure sulfuric acid, and due to its significant role in atmospheric particle formation, three different proxies and one chemical box model calculation were compared to the measured data. The proxies for the sulfuric acid concentration worked reasonably, and with caution, could be applied to other environments.