Global modeling of the C1–C3 alkyl nitrates using STOCHEM-CRI

The atmospheric global budget and distribution of C 1 –C 3 alkyl nitrates have been investigated using a global three-dimensional chemistry transport model, STOCHEM-CRI. Alkyl nitrates (RONO 2 ) are significant NO x reservoir species and the more detailed VOC oxidation mechanism (CRI v2-R5) leads to greater photochemical production. RONO 2 are significant sources of NO x in regions remote from NO x sources. The study shows that the global burden and the atmospheric life-time of C 1 –C 3 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 CH 3 ONO 2 mixing ratios up to 20 ppt over the Amazon rainforest. Up to 15, 10, 2, and 5 ppt of modelled CH 3 ONO 2 , C 2 H 5 ONO 2 , n-C 3 H 7 ONO 2 and i-C 3 H 7 ONO 2 have been found in the northern hemisphere over regions with large anthropogenic emissions of NO x and VOCs. The combination of atmospheric production and long-range transport led to high alkyl nitrate levels at high latitudes. The model performance for C 1 –C 3 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 CH 3 ONO 2 , in both hemispheres are discussed.