Spatiotemporal variation in nonagricultural open fire emissions in China from 2000 to 2007

摘要

Open fires such as those within forests and grasslands, as well as crop residue burning in fields, contribute considerable amounts of trace gases and particulate matter to the atmosphere and therefore play an important role in climate change and atmospheric chemistry. Emissions from open fires in China are estimated at a medium resolution of 1 km~2 from April 2000 to March 2007 (seven fire years). Burned areas and land use types at 1 km spatial resolution are defined using the L3JRC product from the Systeme Probatoire pour l'Observation de la Terre (SPOT) satellite and the Global Land Cover 2000 data sets for China, respectively. The 500-m burned area product (MCD45A1) from the Moderate Resolution Imaging Spectroradiometer (MODIS) is compared with the L3JRC burned area product in China. On an average, the total burned areas from L3JRC product are 16 times those from MCD45A1 product. Interannual changes of burned area are in accordance with the records reported in official statistics. Aboveground biomass densities are characterized by vegetation type and province. Fuel moisture content is considered to calculate the combustion factors by using time series of normalized difference vegetation index (MOD13A3). Crop residue burning accounts for the most biomass burning in China, but we find that it is not detected efficiently by the available burned area algorithms. Both burned area and emission data reveal significant spatial patterns and seasonal variation during the seven fire years. Total nonagricultural fire emissions are concentrated in north and southwest China, especially in the spring and autumn. Forest fires are determined to be the primary contributor to nonagricultural fire emissions. The annual emissions are estimated as follows for China during the seven study years: 137.8 (range from 108.8 to 172.9) Tg a~(-1) CO_2, 7.0 (5.5-8.7) Tg a~(-1) CO, 0.25 (0.22-0.34) Tg a~(-1) NO_x, 0.90 (0.71-1.1) Tg a~(-1) PM_(2.5), 0.06 (0.05-0.07) Tg BC, and 0.56 (0.44-0.7) Tg a~(-1) OC.