Abstract
Although removal of tropospheric methyl bromide (CH3Br) is dominated by the reaction with the seasonally varying hydroxyl (HO) radical concentration, the anticipated corresponding seasonal dependence of CH3Br, as found for other gases with major HO sinks, has been sought previously without success [WMO, 1995]. Our observations of northern hemispheric boundary layer CH3Br concentrations do reveal substantial seasonal changes. The high latitude CH3Br North/South interhemispheric concentration ratio (IHR) varies from a maximum of 1.35±0.04 (1σ) in March–April to 1.10±0.04 in September, with an equal area and seasonally (EAS) weighted average IHR of 1.21±0.03. These observations suggest northern hemispheric emissions are about 15 kilotons/year less than when an IHR of 1.3 is considered [WMO, 1995]. The observed seasonality also partially explains the differences in the IHR reported by several research groups [WMO, 1995] and places needed constraints on the magnitude and seasonality of sources and sinks of CH3Br.
Highlights
Average background concentrations in Alaska and the northernhemisphere(NH) from the March period and 5 other Methyl bromide,with a globalatmosphericmixing ratio of seasonal collections (Table 1 and Figure 2) can be fitted about9 pptv,accountsfor about sinusoidall(yR2 valuesof 0.96and0.98,withpeakto valley half of the total carbon-bondedbromine in the troposphere amplitudesof 2.5 pptv and 1.5 pptv for Alaska and the NH, [WMO, 1995]
CH3Br Interhemispheric Ratios temperatures coupled with high chlorophyll production [Comiso et al, 1993] could lead to large summertimeCH3Br emissions at high southern latitudes [Anbar et al, 1996]
In the limited casesexamined here, the 1.3 interhemispheric concentration ratio CH3Br Seasonal Variability (IHR) always results in about 15 kt/y additional NH CH3Br emissions
Summary
About 15 kilotons/year less than when an IHR of 1.3 is the CH3Br concentrations were substantially enhanced considered [WMO, 1995]. Average background concentrations in Alaska and the northernhemisphere(NH) from the March period and 5 other Methyl bromide,with a globalatmosphericmixing ratio of seasonal collections (Table 1 and Figure 2) can be fitted about9 pptv (partsper trillion by volume),accountsfor about sinusoidall(yR2 valuesof 0.96and0.98,withpeakto valley half of the total carbon-bondedbromine in the troposphere amplitudesof 2.5 pptv and 1.5 pptv for Alaska and the NH, [WMO, 1995].
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