# Effects of Agricultural Biomass Burning on Regional Haze in China: A Review
## 1 Introduction  
Biomass burning is a long-standing agricultural practice, but increasing population and demand for agricultural land and food has had a profound effect on the extent of biomass burning. Globally, farmers use fire as a tool for the removal of agricultural waste and excess crop residue from fields [1]. In China, wood fuel and crop residue burning are the major sources of biomass burning, accounting for nearly 90% of the total biomass burning (based on dry weight), whereas grassland burning is only a minor source of biomass burning [2]. Approximately 140 Tg of agricultural straw is burned in fields every year in China [3].  
Biomass burning contributes large quantities of gases and particulate matter to the atmosphere. Emissions of gaseous pollutants and aerosol particles from biomass burning have a significant impact on air quality, human health, and climate [4, 5] and significantly contribute to the tropospheric radiation budgets on local, regional and even global scales [6, 7, 8]. Due to the substantial effect of biomass burning on air quality and climate, biomass burning emissions and their impact on air quality has been extensively studied in China through ground observation [4, 9], satellite remote sensing [10, 11], and model simulation [12, 13]. There are three approaches to estimating biomass burning emissions: (1) combining statistical data (e.g., product of crop production, residue-to-production ratio, dry matter-to-crop residue ratio, the percentage of dry matter burned in fields, etc.) with the correspondingemission factors [14; 15]; (2) based on the burned area detected by satellites [16; 17]; and (3) based on fire radiative power (FRP) derived from satellite [11; 18]. Generally, compared with statistical data, satellite data overestimate forest burning and underestimate crop residual biomass burning [2], because most biofuel is burned indoors and open field burning of small area is not detected by satellite [2]. In China, the average cultivated area of a farming household is only two acres (0.001334 km\({}^{2}\)) [19]. Open field burning occurs on a small scale and short duration, making it difficult to detect by satellite [14]. [PERSON] et al. [11] estimated emissions from crop burning in fields across the North China Plain using the Moderate Resolution Imaging Spectroradiometer (MODIS) FRP. Their results were consistent with a previous study adopting an agricultural statistical approach [17], but significantly higher than emissions derived from the MODIS burned area product and Global Fire Emissions Database, Version 3.1 (GFEDv3.1, ORNL DAAC, Oak Ridge, TN, USA), respectively. In GFEDv3.1, emission estimation is based on MODIS burned area product. [PERSON] et al. [20] reported that emissions from agricultural fires were likely underestimated in GFEDv3 because some actual agricultural fire activity was not detected. Although study methodologies differ, the purpose of all the studies was to estimate biomass burning emission and analyze the effect of biomass burning on air quality.  
In this paper, we review our present understanding about biomass burning and regional haze status in China in the past few years; discuss the relationship between biomass burning and regional haze in terms of spatio-temporal patterns and chemical composition; and finally provided some suggestions for reducing the effect of biomass burning on regional haze. We conclude that prescribed burning would be a more suitable solution for the disposal of large quantities of substantial agricultural straw in China.