Open burning of rice, corn and wheat straws: primary emissions, photochemical aging, and secondary organic aerosol formation

Abstract

Abstract. Agricultural residues are among the most abundant biomass burned globally, especially in China. However, there is little information on primary emissions and photochemical evolution of agricultural residue burning. In this study, indoor chamber experiments were conducted to investigate primary emissions from open burning of rice, corn and wheat straws and their photochemical aging as well. Emission factors of NO x , NH 3 , SO 2 , 67 non-methane hydrocarbons (NMHCs), particulate matter (PM), organic aerosol (OA) and black carbon (BC) under ambient dilution conditions were determined. Olefins accounted for > 50 % of the total speciated NMHCs emission (2.47 to 5.04 g kg −1 ), indicating high ozone formation potential of straw burning emissions. Emission factors of PM (3.73 to 6.36 g kg −1 ) and primary organic carbon (POC, 2.05 to 4.11 gC kg −1 ), measured at dilution ratios of 1300 to 4000, were lower than those reported in previous studies at low dilution ratios, probably due to the evaporation of semi-volatile organic compounds under high dilution conditions. After photochemical aging with an OH exposure range of (1.97-4.97) × 10 10 molecule cm −3 s in the chamber, large amounts of secondary organic aerosol (SOA) were produced with OA mass enhancement ratios (the mass ratio of total OA to primary OA) of 2.4-7.6. The 20 known precursors could only explain 5.0-27.3 % of the observed SOA mass, suggesting that the major precursors of SOA formed from open straw burning remain unidentified. Aerosol mass spectrometry (AMS) signaled that the aged OA contained less hydrocarbons but more oxygen-and nitrogencontaining compounds than primary OA, and carbon oxidation state (OS c ) calculated with AMS resolved O / C and H / C ratios increased linearly (p < 0.001) with OH exposure with quite similar slopes.

Emission of trace gases and aerosols from biomass burning – an updated assessment

“…To convert between organic carbon and organic matter (OM), a default OM/OC mass ratio of 1.6 is used in the absence of specific information. This value is based on the data from fresh biomass smoke aerosol in the literature (Turpin and Lim, 2001;Aiken et al, 2008;Yokelson et al, 2009;Takahama et al, 2011;Kostenidou et al, 2013;Brito et al, 2014;Collier et al, 2016;Fang et al, 2017;Tkacik et al, 2017;Ahern et al, 2019;Lim et al, 2019). Where only O/C ratios were given, they were converted to OM/OC ratios using the relationship given in Aiken et al (2008).…”

Determination of the Area Affected by Agricultural Burning

“…In this equation, E* i,j (kg/kg) is the emission factor and it describes the amount of pollutant i typically emitted per unit mass of crop j. Multiple studies have been conducted to determine the emission factors associated with agricultural burning under controlled conditions [1] and by field measurements [23]. Table 1 shows E* i,j and L j for several crops.…”

“…They represent the opinion of the scientific community that exposure at or below the level of the TLV does not create an unreasonable risk of disease or injury [3]. Aiming to provide public health protection, including protecting the health of "sensitive" populations such as asthmatics, children, and the elderly, the environmental authority specifies those threshold limit values in the NAAQS for short time periods of exposure (3, 8, or 24 h depending of the pollutant) and for long time periods of exposure (one year) [14][15][16][17][18][19][20][21][22][23][24]. In this work, we only consider short-term exposition, as agricultural burnings are short-term events.…”

Mass Spectral Characterization of Primary Emissions and Implications in Source Apportionment of Organic Aerosol

“…As a result, a new capture vaporizer (CV) with an enclosed cavity was developed (Xu et al, 2017b). Field measurements showed that the CE of CV-AMS was fairly robust at ~1 (Hu et al, 2017).…”