Measurements of gaseous H2SO4 by AP-ID-CIMS during CAREBeijing 2008 Campaign
1Department of Atmospheric Sciences, Texas A&M University, College Station, TX 77843-3150, USA
2State Key Joint Laboratory of Environmental Simulation and Pollution Control, College of Environmental Sciences and Engineering, Peking University, Beijing 100871, China
3Key Laboratory for Urban Habitat Environmental Science and Technology, Shenzhen Graduate School of Peking University, Shenzhen 518055, China
4Leibniz Institute for Tropospheric Research, Permoserstrasse 15, Leipzig 04318, Germany
5Institute für Energie- und Klimaforschung Troposphäre (IEK-8), Forschungszentrum Jülich, 52425 Jülich, Germany
Abstract. As part of the 2008 Campaign of Air Quality Research in Beijing and Surrounding Regions (CAREBeijing 2008), measurements of gaseous sulfuric acid (H2SO4) have been conducted at an urban site in Beijing, China from 7 July to 25 September 2008 using atmospheric pressure ion drift – chemical ionization mass spectrometry (AP-ID-CIMS). This represents the first gaseous H2SO4 measurements in China. Diurnal profile of sulfuric acid is strongly dependent on the actinic flux, reaching a daily maximum around noontime and with an hourly average concentration of 5 × 106 molecule cm−3. Simulation of sulfuric acid on the basis of the measured sulfur dioxide concentration, photolysis rates of ozone and nitrogen dioxide, and aerosol surface areas captures the trend of the measured H2SO4 diurnal variation within the uncertainties, indicating that photochemical production and condensation onto preexisting particle surface dominate the observed diurnal H2SO4 profile. The frequency of the peak H2SO4 concentration exceeding 5 × 106 molecule cm−3 increases by 16% during the period of the summer Olympic Games (8–23 August 2008), because of the implementation of air quality control regulations. Using a multivariate statistical method, the critical nucleus during nucleation events is inferred, containing two H2SO4 molecules (R2 = 0.85). When neither nucleation nor precipitation occurs, the condensation rate of H2SO4 correlates with the daytime sulfate mass concentration of the Aitken mode, but not with that of the accumulation mode aerosols.