Source analysis of volatile organic compounds by positive matrixfactorization in urban and rural environments in Beijing

摘要

This paper applies advance receptor model positive matrix factorization (PMF) sourceanalysis to 1-h resolution VOC data collected at Yufa (rural site) and Peking University, orPKU (urban site), in Beijing. A range of major VOC sources was identified, includingvehicle emissions, liquefied petroleum gas, coal combustion, and biogenic emissions.Vehicle activities contributed approximately 62% of VOC loading and 55% of ozoneforming potential at the PKU site, compared to 38% of VOC loading and 42% of ozoneforming potential at Yufa. These results indicate that the control of vehicle emissions isessential to alleviating VOC pollution, particularly in urban Beijing. We found thatVOC emission strengths are relatively consistent throughout the day in the rural area;variation of mixing height therefore is a controlling factor for ground-level VOCconcentration. In the urban area, both vehicle activity and variation of mixing heightstrongly impact VOC levels. Local sources within Beijing appeared to contribute most ofthe VOCs recorded at both urban and rural areas. However, as some of the VOC speciesare quite reactive, VOC emitted from distant sources would have been depleted duringtransportation, concurrent with the formation of secondary pollutants such as ozone andsulfate. Such depletion would mean that this source apportionment analysis would tend tooverestimate the ozone forming capacity of local VOC sources compared to emissionsfrom distant sources. Nevertheless, this study illustrates that high-resolution VOCmeasurements, especially those with a sampling frequency on the scale of less than 1 day,combined with PMF, can make a strong contribution to our understanding of pollutantemissions and transport characteristics and is a useful tool with which to formulateeffective pollution control strategies.