[Continuous PM Composition Measurements for Source Apportionment During Air Pollution Events].

To explore the application of high-temporal-resolution data in PM source apportionment during air pollution events, ambient air PM components were continuously monitored in urban Nanjing from January to December, 2017. Commercially available instruments for continuous measurements were deployed to obtain hourly concentrations of elements, water-soluble ions, and carbonaceous components of PM. Data for 15 elements and 5 bulk components during three pollution events(firework combustion during the Spring Festival, a spring sandstorm, and a winter haze event) and across the whole year comprised four datasets for source apportionment using positive matrix factorization(PMF), and the distribution of factor/source contributions and estimations of average concentrations of characteristic components were compared based on different input datasets(PMF and PMF). The results showed that the identified factors/sources, factor profiles, and contributions differed largely between PMF and PMF solutions. For example, the relative average contribution of the firework combustion factor derived from the PMF solution(was 1.50%) was far less than that of the PMF solution. The dust factor had an average contribution of 8.51% in the PMF solution, which was approximately double that of the PMF solution. This might be explained by the fact that PMF assumes unvaried source compositions during the measurement campaign, meaning that the source apportionment results based on long-term observations will include bias due to changes in emission sources. Furthermore, during the firework combustion event, the estimated average concentration of K from the PMF solution[(1.32±1.17) μg·m, =0.64]was closer to measured value[(1.36±1.19) μg·m]than that of the PMF solution[(1.16±1.19) μg·m, =0.0090]. For the sand storm event, the concentrations of Fe, Si, and Ti were significantly underestimated by the PMF solution[(0.061±0.042)-(1.06±0.65) μg·m, <0.05], while their peak concentrations agreed well between the PMF estimations and the observations. During the winter haze event, all PM bulk components were well estimated by both the PMF and PMF solutions. Based on these results, PMF source apportionment results based on continuous measurement data during pollution events can reasonably reflect short-term variations in characteristic PM components and their sources, which can improve the timeliness of air pollution source apportionment.