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

摘要

pstrongAbstract./strong 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 NOsubix/i/sub, NHsub3/sub, SOsub2/sub, 67 non-methane hydrocarbons (NMHCs), particulate matter (PM), organic aerosol (OA) and black carbon (BC) under ambient dilution conditions were determined. Olefins accounted for a??&a??span class="thinspace"/span50span class="thinspace"/span% of the total speciated NMHCs emission (2.47 to 5.04span class="thinspace"/spangspan class="thinspace"/spankgsupa??1/sup), indicating high ozone formation potential of straw burning emissions. Emission factors of PM (3.73 to 6.36span class="thinspace"/spangspan class="thinspace"/spankgsupa??1/sup) and primary organic carbon (POC, 2.05 to 4.11span class="thinspace"/spangCspan class="thinspace"/spankgsupa??1/sup), 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 (1.97a??4.97)span class="thinspace"/spana????a??span class="thinspace"/span10sup10/supspan class="thinspace"/spanmoleculespan class="thinspace"/spancmsupa??3/supspan class="thinspace"/spans 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 2.4a??7.6. The 20 known precursors could only explain 5.0a??27.3span class="thinspace"/span% 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 nitrogen-containing compounds than primary OA, and carbon oxidation state (OSsubc/sub) calculated with AMS resolved Ospan class="thinspace"/spana??span class="thinspace"/spanC and Hspan class="thinspace"/spana??span class="thinspace"/spanC ratios increased linearly (ip/ispan class="thinspace"/spana??&a??span class="thinspace"/span0.001) with OH exposure with quite similar slopes./p.