Inorganic trace gases and peroxy radicals during BERLIOZ at Pabstthum: An investigation of the photostationary state of NOx and O3

Abstract

Meteorological and chemical measurements, including peroxy radicals, made during the Berlin Ozone Experiment (BERLIOZ) in summer 1998 at Pabstthum, a rural site about 50 km NW of the city, are described. The analytical techniques and data quality are discussed, including the comparison of different methods deployed side by side at Pabstthum. The highest concentrations of NOx (>20 ppb) and other precursors were observed on days when relatively young air was advected to Pabstthum from the greater Berlin area. NOx often increased during the night due to emissions from the surrounding soils under stagnant conditions with a shallow boundary layer as is evident in the strong negative correlation between nocturnal NO mixing ratios and product of ozone and wind speed. The ozone production rate (PO3) calculated from the photostationary state (PSS) of NOx and O3 increased with NO and reached values of up to 90 ppb h−1. PO3 calculated from NO and the measured peroxy radical concentrations was much lower, around or below 10 ppb h−1. The lower production rates obtained from the peroxy radical measurements are consistent with the ozone budget in the city plume of Berlin. The new JPL recommendation for the rate coefficient of the reaction of NO with O3 slightly improves the disagreement between PSS and measured peroxy radicals. However, another enhancement of 10–20% in the rate coefficient would be required in order to match the results within the uncertainty of the measurements in the high NOx regime. Even then, PSS remains to overpredict PO3 by a factor of 2 at low NOx concentrations. Hence, a yet unidentified process must exist in the atmosphere that converts NO to NO2 without leading to a net production of ozone. The PSS results from other studies are similar as at Pabstthum, suggesting that the overestimation of peroxy radicals and PO3 by the PSS approach is not a particular feature of the conditions at the site.