Two decades of OH variability as inferred by an inversion of atmospheric transport and chemistry of methyl chloroform

[摘要] We developed an iterative inverse method to infer inter-annual sources andsinks of methyl chloroform (MCF) from atmospheric measurements, on a monthlybasis. The methodology is presented and used to estimate two decades of OHvariability between 1980 and 2000, using varying meteorology. When OHconcentrations are adjusted with loose prior errors and MCF emissions areadjusted within inventory bounds, we show that substantial OH inter-annualvariability (8.5±1.0% of the mean) and trend(-0.7%.yr^-1) are necessary to match MCF observations. Thisresult is confirmed by a series of sensitivity tests addressing mainlimitations of previous studies. However, we show that it is also possible tomatch MCF observations with a 65% reduction of OH year-to-year variationsand a 60% reduction of absolute OH trend, but still a consistency ofinferred emissions with inventory values at a ±2σ level. On theother hand, the phase of inferred OH variations is a more robust feature ofour set of inversions. Overall, MCF inversions can only provide a range of OHvariations unless inventory uncertainties are further reduced.

[学科分类] 大气科学