Spatiotemporal variations of ambient PMsub10/sub source contributions in Beijing in 2004 using positive matrix factorization

摘要

Source contributions to ambient PM₁₀ (particles with an aerodynamic diameterof 10 μm or less) in Beijing, China were determined with positive matrixfactorization (PMF) based on ambient PM₁₀ composition data includingconcentrations of organic carbon (OC), elemental carbon (EC), ions and metalelements, which were simultaneously obtained at six sites through January,April, July and October in 2004. Results from PMF indicated that seven majorsources of ambient PM₁₀ were urban fugitive dust, crustal soil, coalcombustion, secondary sulfate, secondary nitrate, biomass burning withmunicipal incineration, and vehicle emission, respectively. In paticular,urban fugitive dust and crustal soil as two types of dust sources withsimilar chemical characteristics were differentiated by PMF. Urban fugitivedust contributed the most, accounting for 34.4% of total PM₁₀ mass on anannual basis, with relatively high contributions in all four months, and evencovered 50% in April. It also showed higher contributions in southwesternand southeastern areas than in central urban areas. Coal combustion was foundto be the primary contributor in January, showing higher contributions inurban areas than in suburban areas with seasonal variation peaking in winter,which accounted for 15.5% of the annual average PM₁₀ concentration.Secondary sulfate and secondary nitrate combined as the largest contributorto PM₁₀ in July and October, with strong seasonal variation peaking insummer, accounting for 38.8% and 31.5% of the total PM₁₀ mass in July andOctober, respectively. Biomass burning with municipal incinerationcontributions were found in all four months and accounted for 9.8% of theannual average PM₁₀ mass concentration, with obviously higher contribution inOctober than in other months. Incineration sources were probably located insouthwestern Beijing. Contribution from vehicle emission accounted for 5.0%and exhibited no significant seasonal variation. In sum, PM₁₀ sourcecontributions in Beijing showed not only significant seasonal variations butalso spatial differences.