Spatial and temporal variability of nonmethane hydrocarbon mixing ratios and their relation to photochemical lifetime

Abstract

The relationship between temporal and spatial variability of C2‐C8 nonmethane hydrocarbon mixing ratios and their HO lifetimes (τ) is presented for samples collected during the 1993 North Atlantic Regional Experiment (NARE) and from other urban and remote sites. The C2‐C4 alkanes, acetylene and benzene typically define a trend of the form slnx = Aτ−b where slnx is the standard deviation of the ln of the mixing ratio. The relationship extended over a wider range of hydrocarbons in winter. The exponent b ranged in value from 0.28±0.023 for winter urban data where C2‐C8 hydrocarbons defined a strongly correlated trend, to 0.56±0.15 for C2‐C4 hydrocarbons at a coastal site in Nova Scotia during NARE. The trends are significantly different from that given by the Junge relationship [Junge, 1974]. Data from the Azores do not display such a trend and were likely influenced by local emissions. Variance trends are a useful analytical tool for examining the validity of hydrocarbon measurements.