Emission of polycyclic aromatic hydrocarbons from indoor straw burning and emission inventory updating in China.

The emission factors for indoor straw combustion are a major data gap for estimating the polycyclic aromatic hydrocarbon (PAH) emissions in China. The emission factors for open-fire straw burning were borrowed from our previous study and a rough estimate was developed. As one of the most important emission sources in China, the emission factors for indoor straw combustion needed to be determined and revised accurately. In this study, a representative straw in rural China was collected and burned in similar conditions with those used by countryside families. The smoke produced was sampled and the PAH concentrations were analyzed by gas chromatography-mass selective detection (GC-MSD), and much higher emission factors were found. Based on the newly measured emission factors, the emission amount from indoor straw combustion was updated. In addition, recently published emission factors were compiled in a comprehensive database and some new sources were included. Additionally, the emission inventory was extended to cover the period from 1950 to 2005 and upgraded to a scale resolution of one kilometer. In the updated inventory, the total quantity of 16 PAHs emitted from China was 116,000 tons in 2003, with indoor straw and firewood combustions as the most important sources. Although vehicular emission contributed a relatively small percentage of the total emission, it was still one of the major sources in the urban areas of China. The total PAH emission increased continuously for four decades, starting from 1950, but fluctuated since 1990 due to variations in coke production.