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

The relationship between temporal and spatial variability of C 2 ‐C 8 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 C 2 ‐C 4 alkanes, acetylene and benzene typically define a trend of the form s lnx = Aτ −b where s lnx 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 C 2 ‐C 8 hydrocarbons defined a strongly correlated trend, to 0.56±0.15 for C 2 ‐C 4 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.