Model analysis of trace gas measurements and pollution impact during INDOEX

An analysis of acetone (CH3COCH3) and acetonitrile (CH3CN) measurements, pe rformed during the Indian Ocean Experiment (INDOEX), using a chemistry gene ral circulation model is presented. A comparison with measurements indicate s that the model simulates realistic CO and acetone distributions, except t oward the Indian west coast near the surface. The latter may be related to a sea breeze circulation at the Indian west coast, which is not resolved by the model. A comparison of the measured and modeled correlation between CO and acetone indicates the presence of a background marine acetone source. A model sensitivity study suggests a global marine emission strength of 15- 20 Tg acetone yr(-1), which is a significant contribution to the estimated global acetone source of 56 (37-80) Tg acetone yr(-1). The comparison of me asured and modeled CO-acetonitrile correlation from surface measurements in dicates that a model sink of acetonitrile in the marine boundary layer is m issing. A model sensitivity study suggests that this could be dry depositio n (deposition velocity estimate: 0.01-0.05 cm s(-1)) on the ocean surface. A comparison of measured and modeled tropospheric acetonitrile indicates th at the model overestimates the free tropospheric acetonitrile mixing ratios up to a factor of 3, which points to a missing free tropospheric sink of a cetonitrile in the model. A possible explanation may be stratospheric loss and subsequent stratosphere-troposphere exchange, which was not included in the model.