Night‐time NO₃ and OH radical concentrations in the United Kingdom inferred from hydrocarbon measurements

Abstract

Abstract The hydrocarbon decay method (Rivett et al. , 2003 ) has been used to analyse hydrocarbon data from four contrasting sites in the United Kingdom to estimate night‐time levels of NO 3 and OH. Remarkably consistent results emerge using alkenes, revealing NO 3 and OH levels in the range of 0.01–10 ppt and 1 × 10 4 − 1 × 10 6 molecule cm −3 , respectively. Weak seasonal cycles are observed where NO 3 levels peak in spring and OH in summer. Analysis using alkanes suggests that Cl atom levels of around 2 × 10 4 molecule cm −3 may be present. How Cl may be formed at night in such high quantities is unknown and may not be the answer to the disparity between the two methods. Copyright © 2008 Royal Meteorological Society