There have been dramatic changes in the chemistry of the troposphere over the period of rapid industrialisation during this century. There is evidence that tropospheric ozone has doubled in the Northern Hemisphere in this time, and modelling studies have suggested significant changes in the ability of the atmosphere to remove pollutants (the `oxidising capacity'). Direct measurements of photooxidant chemistry have, however, only been made in recent years, whilst measurements of the trace gases which drive this chemistry extend back only to the late 1970s.
This project aims to use "firn air" - air trapped in deep polar snow - to examine the record of trace gases in both the Northern and Southern hemispheres over the last 80 to 100 years. Unlike ice cores, firn extraction yields large volumes (tens of litres) of air for analysis. This allows samples to be circulated between laboratories for repeated analysis of different suites of trace gases at ultra-trace levels. This will enable a detailed picture of the atmospheric composition to be built up in air of different ages. Extensive modelling studies will then be conducted to determine the trends of short-lived reactive species such as ozone, hydroxyl radical, peroxide, formaldehyde, and reactive oxides of nitrogen. Hence we will determine the extent of human impact on the trace gas composition and photooxidant chemistry of the troposphere.
In summary, the objectives of FIRETRACC/100 are as follows
- To determine the global trends of trace gases relevant to troposphericchemistry over the 20th century. These will include CO, the isotopiccomposition of CO, hydrocarbons, alkyl nitrates, numerous OH-reactivehalocarbons (such as methyl chloride, methyl chloroform, methyl bromide,hydrochlofluorocarbons, etc.), and sulphur gases (COS, CS2, etc.). Trends oflonger lived gases will also be determined for dating purposes (CO2, CFCs,SF6, perfluorocarbons, etc.)
- Determine the evolution of inter-hemispheric ratios of OH-sensitive speciesto constrain modelled global OH fields
- Examine ratios of parent hydrocarbons to alkyl nitrates to place constraintson NOX fields in models
- Elucidate the sources of CO from isotopic studies and use to deconvoluteCO/methane coupling in models
- Reconstruct the history of ozone, OH and tropospheric oxidising capacity overthe past 100 years using full chemistry 2-D models
- Determine the influence of 20th century industrialisation on the gas phasecomposition and chemistry of the lower atmosphere
Funding SchemeCSC - Cost-sharing contracts
CB3 0ET Cambridge