Trace gas mixing ratio variability versus lifetime in the troposphere and stratosphere: Observations

B T Jobson,D R Blake,F C Fehsenfeld,A H Goldstein,S M Schauffler,D D Parrish,J W Elkins,S A Mckeen

doi:10.1029/1999jd900126

Abstract

Several archived data sets have been reviewed to examine the relationship between mixing ratio variability and lifetime for hydrocarbon and halocarbon species in the troposphere and stratosphere. The dependence on lifetime was described by the power law relationship slnX = Aτ−b where slnX is the standard deviation of the ln of the mixing ratios, A is a proportionality coefficient, and b is an exponent that relates to the dominance of sink terms in the regional variability budget. At the Harvard forest ground site, winter and summer data displayed the same lifetime dependence, τ−0.18, which was significantly weaker than the τ−0.5 dependence of remote tropospheric data, indicating that source terms dominated regional variability at Harvard. In addition, the ratio of summer to winter slnX values was found to be similar for all species except ethane, averaging 1.54±0.04. This ratio is consistent with a factor of 11 seasonal change in the species lifetimes, given a τ−0.18 lifetime dependence. Stratospheric data displayed a stronger lifetime dependence than tropospheric trends, indicating a more dominant role for sink terms in describing spatial variability in this region of the atmosphere. We show that a unique power law relationship between slnX ratios for two species Xi and Xj and the kinetic slope of ln(Xi) versus ln lpar;Xj) correlation plots is found to hold in both observations and theory. Thus knowledge of the coefficient b allows for a clearer understanding of the relationship between observed slopes of ln (Xi) versus ln (Xj) correlation plots and the ratio of the species lifetimes.

Highlights

The relationshipbetweentracegasmixing ratio variability in the atmosphereand atmosphericlifetime has not been widely studiedeither from observationsor from a theoretical standpoint.The mostwidely citedreferenceis Junge [1974], who found an empirical relationship between the global spatialvariability of severaltracegasesin the troposphereand their steadystatelifetimes
Where relative standarddeviation (RSD) is the relative standard deviationand x is the residencetime in years
Jobson et al [1998] examined the variability-lifetime relationshipsfor nonmethanehydrocarbonson a regional scale

Summary

Introduction

The relationshipbetweentracegasmixing ratio variability in the atmosphereand atmosphericlifetime has not been widely studiedeither from observationsor from a theoretical standpoint.The mostwidely citedreferenceis Junge [1974], who found an empirical relationship between the global spatialvariability of severaltracegasesin the troposphereand their steadystatelifetimes. Jobson et al [1998] examined the variability-lifetime relationshipsfor nonmethanehydrocarbonson a regional scale. They proposedusingthe standarddeviationof theIn of themixingratios(SlnXa) sthemeasureof variabilityratherthan the relative standarddeviation (RSD) used by Junge [1974]. Tracer variability- with respecto usingvariability-lifetimerelationshiptso infer lifetime relationships have not been examined in the relative oxidant abundances. Our AtmosphericGas Experiment(GAGE) monitoring network previousanalysis [Jobsonet al., 1998] examinedthe relative [Prinn et al, 1995] provide a referencelifetimeto whichother variability for hydrocarbons that were oxidized by HO long lived gases can be scaled [Prather and exclusively. CH3C1 and CH3Br were scaledto the 4.9 year global mean in this studythe variability of specieslost by HO are compared lifetime of CH3CC13due to removalby HO accordingto with those lost by photolysis and the absolute value of Prather and Spivakovsky[1990]. - z coefficientsusedto calculatelifetimesare given in Table 1, andthe resultinglifetimesare givenin Table 2

Tropospheric Data

StratosphericData

I I CFC-11