The part of the solar spectrum with the highest influence on the formation of SOA in the continental boundary layer

[摘要] The relationship between nucleation events and spectral solar irradiance wasanalysed using two years of data collected at the Station for Measuring ForestEcosystem-Atmosphere Relations (SMEAR II) in Hyytiälä, Finland. We analysed thedata in two different ways. In the first step we calculated ten nanometer averagevalues from the irradiance measurements between 280 and 580 nm and explored ifany special wavelengths groups showed higher values on event days compared to aspectral reference curve for all the days for 2 years or to reference curves for everymonth. The results indicated that short wavelength irradiance between 300 and340 nm is higher on event days in winter (February and March) compared to the monthlyreference graph but quantitative much smaller than in spring or summer. By buildingthe ratio between the average values of different event classes and the yearlyreference graph we obtained peaks between 1.17 and 1.6 in the short wavelengthrange (300--340 nm). In the next step we included number concentrations of particlesbetween 3 and 10 nm and calculated correlation coefficients between the differentwavelengths groups and the particles. The results were quite similar to thoseobtained previously; the highest correlation coefficients were reached for the spectralirradiance groups 3--5 (300--330 nm) with average values for the single event classesaround 0.6 and a nearly linear decrease towards higher wavelengths groups by30%. Both analyses indicate quite clearly that short wavelength irradiance between 300and 330 or 340 nm is the most important solar spectral radiation for the formation ofnewly formed aerosols. In the end we introduce a photochemical mechanism as onepossible pathway how short wavelength irradiance can influence the formation of SOAby calculating the production rate of excited oxygen. This mechanism shows in whichway short wavelength irradiance can influence the formation of new particles eventhough the absolute values are one to two magnitudes smaller compared to irradiancebetween 400 and 500 nm.

[学科分类] 大气科学