Determination of photolysis frequencies of ozone and nitrogen dioxide during SANA 2: The influence of tropospheric aerosol particles

Abstract

Photolysis of ozone and nitrogen dioxide is of vast importance for tropospheric chemistry. Model calculations of photolysis frequencies are available only for cloudless sky and some cases of stratiform cloud cover, whereas direct measurements using photoelectric detectors can provide data for all atmospheric conditions. Half-hourly mean values of ozone (j(O1D) and nitrogen dioxide (j(NO2)) photolysis frequencies for the period of the SANA 2 campaign at Melpitz are presented. j(O1D) was measured directly with a time resolution of one minute, while j(NO2) was evaluated by a parameterization using measured global radiation data. For low elevation above sea level, as given at Melpitz (about 80 m a.s.l.), a linear relationship between global radiation and j(NO2) is found. Maximum 30-minute averages at noontime reach 1.5·10-5 s-1 for j(O1D) and 1.0·10-2 s-1 for j(NO2), while the one minute maximum of j(O1D) exceeds 1.6·10-5 s-1. A period of high atmospheric aerosol load shows a distinct influence of atmospheric turbidity on measured ozone photolysis frequency near the ground. A comparison with model calculations provides a good agreement regarding the zenith angle dependence of j(O-1D) due to changes in the aerosol optical thickness τ. Absolute values of j(O1D) and j(NO2) determined in this work agree within the given uncertainties with measurements and model calculations published before. In addition, the effect of uncertainties in existing O(1D) quantum yield data on the determination of j(O1D) is discussed.

Keywords

• photolysis
• ozone
• photoelectric
• atmospheric turbidity
• photolyse
• ozon
• photoelektrisch
• atmosphärische trübung
• melpitz
• germany