[Wildfire smoke injection heights in China based on multi-angle imaging spectroradiometer (MISR) observations]

Smoke injection height is a key driving factor for plume transport, which determines the lifetime of smoke aerosol in the atmosphere, transport path and diffusion along with the wind, and impacts on atmospheric environment. In this study, raw data obtained from the latest multi-angle imaging spectroradiometer (MISR) plume height project was extracted and analzyed. The variation of smoke injection heights of wildfire in China was investigated with statistical analysis methods. The effects of fire characteristics (combustion biomass type and fire radiative power) on the smoke injection height were explored. Meanwhile, the influence of smoke injection heights on the atmospheric environment was discussed based on the proportion of higher injection height plumes and the value of smoke aerosol optical depth (AOD). The results showed that smoke injection heights from wildfire ranged from 345 to 7719 m, with 57.1% of which ranging from 500 to 1000 m. Except for an abnormally high value of smoke injection height from a large grassland fire, the rest of smoke injection heights were lower than 3000 m. The biomass type for combustion was an important factor affecting smoke injection heights. The injection heights of the plume caused by forest fire were the highest and had the greatest variability. Smoke injection heights increased with the fire radiation power, but with obvious dispersion (R²=0.19). By setting a simple threshold, the proportion of higher injection plumes which might cause long-distance transportation of air pollutants in China was 10.5%. Combined with the analysis of smoke AOD, it was found that the average smoke injection height from cropland burning was the lowest, but their smoke caused the highest regional air pollution. In contrast, although forest fires could produce the highest smoke injection height, their smoke had a lower average value of AOD, which indicated a relatively weak impact of forest fires on regional air quality.