Sensitivity of tropospheric chemistry to the source of NO x from lightning : sensitivity simulations with the global 3D chemistry model for atmospheric transport and chemistry MATCH-MPIC

The impact of different assumptions concerning the source magnitude as well as the vertical placement of lightning-produced nitrogen oxides is studied using the global chemistry transport model MATCH-MPIC. The responses of NOx, O3, OH, HNO3 and peroxyacetyl-nitrate (PAN) are investigated. A marked sensitivity to both parameters is found. NOx burdens globally can be enhanced up to 100% depending on the vertical placement and source magnitude strength. The global mean OH concentration and the tropospheric oxidizing efficiency are also strongly sensitive, with effects comparable to, or larger than, those on O3. In all cases, the largest enhancements occur in the tropical upper troposphere, where lifetimes of most trace gases are longer and where they thus become more susceptible to long-range transport by large-scale circulation patterns. Comparison with observations indicate that the 0 and 20 Tg/yr(N) production rates of NOx from lightning are too low and too high a source magnitude, respectively. However, no single intermediate production rate or vertical distribution can be singled out as best fitting the observations due to the large scatter in the datasets. This underscores the need for further measurement campaigns in key regions, particularly in the tropical continents, where lightning is prevalent