Abstract
Abstract. Nitrogen oxides (NOx) play key roles in atmospheric chemistry, air pollution, and climate. While the largest fraction of these reactive gases is released by anthropogenic emission sources, a significant amount can be attributed to vegetation fires. In this study, NO2 from GOME-2 on board EUMETSAT's MetOp-A and OMI on board NASA's Aura as well as fire radiative power (FRP) from the measurements of MODIS on board NASA's Terra and Aqua satellites are used to derive fire emission rates (FERs) of NOx for different types of vegetation using a simple statistical approach. Monthly means of tropospheric NO2 vertical columns (TVC NO2) have been analyzed for their temporal correlation with the monthly means of FRP for five consecutive years from 2007 to 2011 on a horizontal 1° × 1° grid. The strongest correlation is found to be largely confined to tropical and subtropical regions, which account for more than 80% of yearly burned area, on average, globally. In these regions, the seasonal variation of fire intensity, expressed by the FRP data, is similar to the pattern of TVC NO2. As chemical models typically require values for the amount of NOx being released as a function of time, we have converted the retrieved TVC NO2 into production rates of NOx from fire (Pf) by assuming a constant lifetime of NOx. The comparison between Pf and NOx emissions from the Global Fire Emissions Database (GFEDv3.1) over 5 characteristic biomass burning regions in the tropics and subtropics shows good agreement. By separating the monthly means of Pf and FRP according to land cover type, FERs of NOx could be derived for different biomes. The estimated FERs for the dominating types of vegetation burned are lowest for open shrublands and savannas (0.28–1.03 g NOx s−1 MW−1) and highest for croplands and woody savannas (0.82–1.56 g NOx s−1 MW−1). This analysis demonstrates that the strong empirical relationship between TVC NO2 and FRP and the following simplified assumptions are a useful tool for the characterization of NOx emission rates from vegetation fires in the tropics and subtropics. Possible factors affecting the magnitude of the obtained values are discussed.
Highlights
Nitric oxide (NO) and nitrogen dioxide (NO2) are coupled in the atmosphere as NO2 is photolyzed to produce NO and an oxygen atom (O), which reacts with molecular oxygen (O2) to produce ozone (O3)
We derive the gradient of the linear relationship between the converted TVC NO2, here referred to as production rate of Nitrogen oxides (NOx) from fire (Pf), and fire radiative power (FRP) over characteristic tropical and subtropical biomass burning regions
The gradients, here referred to as fire emission rates (FERs) of NOx, for the morning fires are obtained from the relationship between Pf, retrieved from Global Ozone Monitoring Experiment (GOME)-2 (OMI) and converted according to Eqs. (7) and (8), and FRP, retrieved from MODerate resolution Imaging Spectroradiometers (MODIS) on board Terra (Aqua)
Summary
Nitric oxide (NO) and nitrogen dioxide (NO2) are coupled in the atmosphere as NO2 is photolyzed to produce NO and an oxygen atom (O), which reacts with molecular oxygen (O2) to produce ozone (O3). Major sources of NOx are attributed to anthropogenic activities (e.g., high temperature combustion processes), biomass burning (intentional and accidental), soil microbial production from the oxidation of ammonium ions (NH+4 ) and the reduction of nitrate ions (NO−3 ), and lightning strikes (Lee et al, 1997). Minor tropospheric sources of NOx include the oxidation of ammonia (NH3), and the reaction of O(1D), which is produced by the photolysis of O3 in the UVB (280–320 nm) and to a minor extent in the UVA (320–400 nm) with nitrous oxide (N2O) (Olivier et al, 1994). Schreier et al.: Empirical estimates of NOx emission rates from fire
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