Particulate matters emitted from maize straw burning for winter heating in rural areas in Guanzhong Plain, China: Current emission and future reduction

Maize straw smoldering in “Heated Kang” is the traditional way for heating in winter in rural areas of Guanzhong Plain. This smolder procedure produced large quantities of pollutants and got more and more concern from both public and researchers. In this study, on-site measurements of straw smoldering in a residence with a Chinese ‘Heated Kang’ (Scenario 1) were done to determine the emissions factors (EFs) for pollutants. Moreover, EFs of pollutants from an advanced stove fired with maize straw (Scenario 2) and maize-straw pellet (Scenario 3) had been conducted in a laboratory to find the new measure to reduce the pollution emissions. The results showed that the EFs of PM_2.5 for three scenarios were 38.26 ± 13.94 g·kg^{− 1}, 17.50 ± 8.29 g·kg^{− 1} and 2.95 ± 0.71 g·kg^{− 1}, respectively. Comparing EFs of pollutants from 3 scenarios indicates that both briquetting of straw and advanced stove with air distribution system could efficiently reduce pollutants emission especially for Scenario 3. In detail, EFs of PM_2.5, OC, EC and water soluble ions all have over 90% reduction between Scenarios 1 and 3. All particle-size distributions were unimodal, and all peaked in particle sizes < 0.47 μm. The EFs for K⁺ and Cl⁻ were the highest of cations and anions for the majority of size groups. Converting to pellets and advanced stoves for residential heating could reduce PM_2.5 emission from 48.3 Gg to 3.59 Gg, OC from 19.0 Gg to 0.91 Gg, EC from 1.7 Gg to 0.17 Gg and over 90% reduction on total water soluble ions in the whole region. A box model simulation for the Guanzhong Plain indicated that this conversion would lead to a 7.7% reduction in PM_2.5 (from 130 to 120 μg·m^{− 3}) in normal conditions and a 14.2% reduction (from 350 to 300 μg·m^{− 3}) in hazy conditions. The results highlighted that the straw pellets burning in advanced stove can effectively reduce pollutants emitted and improve the energy use efficiency in comparison with maize straw smoldering in “Heated Kang”. The study supplies an effective measure to reduce the rural biomass burning emission, and this method can be used in not only Guanzhong Plain but also other undeveloped areas in the future.