No abstract

Soot, mainly derived from incomplete combustion of fossil fuel and biomass, exists ubiquitously in different environmental matrixes. To study the detrimental effects of soot on climate, air quality, and human health, accurate quantification of soot is an important prerequisite. However, until now, quantification of soot in environmental media, especially in carbonaceous media, is still very challenging. Here, we report a matrix-free laser desorption/ionization mass spectrometry (LDI-MS) method for in situ imaging of soot particles in size-segregated aerosol samples collected on filter membranes. A series of round-shaped sample spots in filter membranes were selected and subjected to MS imaging analysis, enabling direct in situ quantification of soot without solvent extraction or separation. Especially, the MS imaging with serial sample spots can overcome the problems of sweet-spot in LDI-MS and inhomogeneous distribution of soot in the filter membrane, thus greatly improving the precision of quantification. The limit of detection of soot was 4 ng/m 2 and the recovery was 84.4−126%. By using this method, we found that a higher soot content was present in larger-sized particulate matter than smaller-sized particles, suggesting that aerosol soot was mainly derived from primary emission sources. Furthermore, this method also shows the potential to analyze nitrate and sulfate species in PM 2.5 . To the best of our knowledge, it is the first method capable of simultaneous analysis of inorganic salts and soot in air samples. It represents a novel strategy for in situ quantification of aerosol soot with the advantages of high specificity, high sensitivity, separation-, solvent-and matrix-free.

Microplastics (MPs), as a new persistent pollutant, can be emitted and accumulated in urban environments, but there is no detailed information on the driving factors of MP pollution. In this study, through a large-scale wetland soil survey, the features of MPs were characterized in each urban area. The results showed an average abundance to be 379 n/kg in wetland soil. Polypropylene, fiber or fragment, and black color were common composition, shape, and color, respectively. The spatial distribution information showed that MP abundance was significantly relevant to the distance from the urban economic center. Furthermore, the correlation and regression analysis revealed that MP abundance was related to soil heavy metal and atmospheric particle (PM10 and PM2.5) concentrations (P < 0.05), while the promotion of socioeconomic activities (urbanization level, population density, etc.) may aggravate the pollution degree. Additionally, by using structural equation modeling, it was found that the urbanization level was the dominant factor driving the MP pollution degree, with a total effect coefficient of 0.49. Overall, this work provides multi-sided environmental information regarding MP pollution in urban ecosystems, which is significant for follow-up studies of MP pollution control and restoration.