In-Situ Measurements of HCN and CH3CN In the Pacific Troposphere: Sources, Sinks, and Comparisons with Satellite Observations

A new capillary gas chromatographic method using a Reduction Gas Detector was developed to measure HCN and CH3CN in the remote troposphere. This instrumental configuration was deployed for the very first time in the Trace-P field mission performed during the spring of 2001. The NASA DC-8 aircraft afforded an opportunity to measure HCN and CH3CN in polluted and pristine environments over the Pacific to a maximum altitude of 12 km. These are some of the first in situ measurements of the distribution of HCN and CH3CN over the Pacific. Large background concentrations of both nitriles were found to be present and significant variability was observed. The abundance of HCN and CH3CN was strongly impacted by outflow of pollution from Asia. In general there appeared to be a direct but nonlinear relationship between the mixing ratios of HCN and CH3CN. The vertical structure of these chemicals shows direct evidence of the presence of a significant oceanic sink. These observations will be compared with the column content HCN data from satellites and other available measurements. A large body of data have been collected and are being analyzed, both statistically and with the help of models, to better understand the sources and sinks of these nitriles. These results will be presented.