Abstract
Abstract. Biomass burning represents both a significant and highly variable source of NOx to the atmosphere. This variability stems from both the episodic nature of fires, and from fire conditions such as the modified combustion efficiency of the fire, the nitrogen content of the fuel and possibly other factors that have not been identified or evaluated by comparison with observations. Satellite instruments offer an opportunity to observe emissions from wildfires, providing a large suite of measurements which allow us to study mean behavior and variability on the regional scale in a statistically rigorous manner. Here we use space-based measurements of fire radiative power from the Moderate Resolution Imaging Spectroradiometer in combination with NO2 tropospheric column densities from the Ozone Monitoring Instrument to measure mean emission coefficients (ECs in g NO MJ−1) from fires for global biomes, and across a wide range of smaller-scale ecoregions, defined as spatially-distinct clusters of fires with similar fuel type. Mean ECs for all biomes fall between 0.250–0.362 g NO MJ−1, a range that is smaller than found in previous studies of biome-scale emission factors. The majority of ecoregion ECs fall within or near this range, implying that under most conditions, mean fire emissions of NOx per unit energy are similar between different regions regardless of fuel type or spatial variability. In contrast to these similarities, we find that about 24% of individual ecoregion ECs deviate significantly (with 95% confidence) from the mean EC for the associated biome, and a similar number of ecoregion ECs falls outside the range of all mean biome ECs, implying that there are some regions where fuel type-specific global emission parameterizations fail to capture local fire NOx emissions.
Highlights
Biomass burning emissions induce a variety of effects to climate and air quality
In Mebust et al (2011) we found that the relative differences between grass, shrub and forest fire emission coefficient (EC) derived from Ozone Monitoring Instrument (OMI) and Moderate Resolution Imaging Spectroradiometer (MODIS) data reproduced similar relative differences in EFs measured for primarily North American fires in situ
We present biome- and ecosystem-resolved NOx ECs, based on satellite measurements of tropospheric NO2 from OMI and of fire radiative power (FRP) from MODIS, for several different biome and ecosystem categories
Summary
Biomass burning emissions induce a variety of effects to climate and air quality. They impact the global radiative budget directly by absorbing or reflecting incoming radiation, e.g. CO2 and aerosols, and/or indirectly by influencing the chemistry or physics of climate forcers, e.g. nitrogen oxides (NOx = NO + NO2) and CO acting as ozone (O3) precursors or aerosol indirect impacts on clouds (Bowman et al, 2009; Fiore et al, 2012; Jaffe and Wigder, 2012). Current models of fire emissions rely on a biomass-burned approach: to estimate the mass of a compound emitted, an emission factor (EF in g kg−1 biomass burned) derived from in situ measurements of smoke is multiplied by an estimate of the total biomass burned, often calculated as the product of other factors, e.g. burn area, fuel loading, combustion completeness (Andreae and Merlet, 2001; Wiedinmyer et al, 2006; van der Werf et al, 2010) This strategy has weaknesses, as the uncertainty in biomass burned for a particular fire is high, and even aggregate estimates at lower spatial and temporal resolution can have significant biases (van der Werf et al, 2010; Granier et al, 2011). We focus on emissions of NOx, which
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