Sulphuric acid closure and contribution to nucleation mode particle growth

[摘要] Sulphuric acid concentrations were measured and calculated based on pseudosteady state model with corresponding measurements of CO, NO_x, O₃,SO₂, methane and non-methane hydrocarbon (NMHC) concentrations as wellas solar spectral irradiance and particle number concentrations with sizedistributions. The measurements were performed as a part of the EU projectQUEST (Quantification of Aerosol Nucleation in the European Boundary layer)during an intensive field campaign, which was conducted in Hyytiälä,Finland in March–April 2003. In this paper, the closure between measured andcalculated H₂SO₄ concentrations is investigated. Besides that,also the contribution of sulphuric acid to nucleation mode particle growthrates is studied. Hydroxyl and hydroperoxy radical concentrations weredetermined using a pseudo steady state box model including photo stationarystates. The maximum midday OH concentrations ranged between 4.1×10⁵ to1.8×10⁶ molecules cm^-3 and the corresponding values for HO₂were 1.0×10⁷ to 1.5×10⁸ molecules cm^-3.The dominant sourceterm for hydroxyl radicals is the reaction of NO with HO₂ (56%) andthe reaction of CO with OH covers around 41% of the sinks. The sulphuricacid source term is the reaction SO₂ with OH and the sink term iscondensation of sulphuric acid. The closure between measured and calculatedsulphuric acid concentrations is achieved with a high agreement to themeasured values. In sensitivity studies, we used different values for thenon-methane hydrocarbons, the peroxy radicals and nitrogen dioxide. The bestfits between calculated and measured values were found by decreasing theNO₂ concentration when it exceeded values of 1.5 ppb and doubling thenon-methane hydrocarbon concentrations. The ratio, standard deviation andcorrelation coefficient between measured and calculated sulphuric acidconcentrations are 0.99, 0.412 and 0.645, respectively. The maximum middaysulphuric acid concentrations varied between 3×10⁵ to1.9×10⁷ molecules cm^-3 for the measurements and3×10⁵ to 1.4×10⁷ molecules cm^-3for the calculations, respectively. An averageparticipation of sulphuric acid to the nucleation mode particle growth ratesis 8.8%. Classifying the days into two groups – ''polluted'' days withair masses originated over Central Europe or UK, and ''cleaner'' days withair masses originated over the Northern Atlantic or the Polar regions –reflects an equal sulphuric acid contribution to the aerosol growth in bothair mass classes.

[学科分类] 大气科学