Global modeling of the C1–C3 alkyl nitrates using STOCHEM-CRI. (December 2015) - Khan, M.A.H.
Abstract: The atmospheric global budget and distribution of C1 –C3 alkyl nitrates have been investigated using a global three-dimensional chemistry transport model, STOCHEM-CRI. Alkyl nitrates (RONO2 ) are significant NOx reservoir species and the more detailed VOC oxidation mechanism (CRI v2-R5) leads to greater photochemical production. RONO2 are significant sources of NOx in regions remote from NOx sources. The study shows that the global burden and the atmospheric life-time of C1 –C3 alkyl nitrates are 113 Gg and 9–10 days, respectively, which are in excellent agreement with estimates established by previous studies. The abundance of alkyl nitrates have been found to be higher in the continental atmosphere, with CH3 ONO2 mixing ratios up to 20 ppt over the Amazon rainforest. Up to 15, 10, 2, and 5 ppt of modelled CH3 ONO2, C2 H5 ONO2, n-C3 H7 ONO2 and i-C3 H7 ONO2 have been found in the northern hemisphere over regions with large anthropogenic emissions of NOx and VOCs. The combination of atmospheric production and long-range transport led to high alkyl nitrate levels at high latitudes. The model performance for C1 –C3 alkyl nitrates was established using observations from nine flights and nine field campaigns. The comparison shows a tendency towards model under-prediction of the observations, particularly in the southern hemispheric marine boundary layer, possibly due to the absence of oceanic production mechanisms and air-sea exchange processes in the model. The discrepancies between model and observed seasonal cycles, especially of CH3 ONO2, in both hemispheres are discussed. Highlights: The tropospheric global burden of C1 –C3 alkyl nitrates is found to be 113 Gg. Up to 20 ppt CH3 ONO2 is found over the Amazon rainforest. RONO2 are significant sources of NOx in remote regions. Good agreement between model and observations is found in the upper troposphere.