•HMW PAHs were more homogeneously distributed compared to LMW PAHs.•Suburban sites were subjected to higher BaPeq values in winter, suggesting higher health risks.•Vehicle emission was a major source of PAHs (32–43%) in urban and urban buildup areas.•Biomass and coal combustion were major sources in suburban areas in winter.Atmospheric particulate polycyclic aromatic hydrocarbons (PAHs) have been drawing sustained attention due to their health risk and effects on air pollution. It is essential to determine the main sources and reduce atmospheric levels of PAHs to protect human health. PAHs in PM2.5 have been detected at five sites located in five districts in Shanghai, a modern metropolitan city in China. Spatial and temporal variations of composition profiles and sources of PAHs at each site in each season were investigated. The results showed that atmospheric particulate PAHs level in Shanghai was the lowest in summer and the highest in winter, dominated by high molecular weight (HMW) PAHs. Analysis with a combination of coefficients of Pearson's correlation and coefficient of divergences indicated heterogeneous spatial and temporal distribution for LMW PAHs and homogenous distribution for HMW PAHs. Diagnostic ratios and positive matrix factorization (PMF) model both identified pyrogenic sources as the main contributor of PAHs in Shanghai, with vehicular source contribution of 32– 43% to the total PAHs annually and around 20% from biomass burning emissions in urban and urban buildup areas. While in winter, coal combustion and biomass burning could act as two major sources of PAHs in suburban areas, which could contribute to > 70% of total PAHs measured in PM2.5 in Shanghai.Download high-res image (211KB)Download full-size image

The idea of single particle aerosol mass spectrometry was first proposed in the 1970s and then developed quickly in recent two decades. Because it can simultaneously provide much information including particle size distribution, composition of multiple chemical species and mixing state for each single particle with high-time resolution, single particle aerosol mass spectrometry has been widely applied in the area of environmental monitoring and fine particulate matter research. This review aims to (1) provide an introduction of the development history and progress of single particle aerosol time-of-flight mass spectrometry, (2) summarize its principle, methods for data analysis, output of results and its applications in environmental measurement and research using two major commercialized instruments (ATOFMS and SPAMS), and (3) provide suggestions for future research.By analyzing particles in high-time resolution, single particle aerosol mass spectrometry can provide physical and chemical properties for every particle, i.e. size and mass spectrum. Through specific softwares and clustering methods, particles can be classified into several types by the similarities of their spectra. The information mentioned above can be used to study the sources, mixing state and aging process of particles.

Analyzing the radiocarbon (14C) content of polycyclic aromatic hydrocarbons (PAHs) in atmospheric particulate matter can provide estimates on the source contributions from biomass burning versus fossil fuel. The relative importance of these two sources to ambient PAHs varies considerably across regions and even countries, and hence there is a pressing need to apportion these sources. In this study, we advanced the radiocarbon analysis from bulk carbon to compound class specific radiocarbon analysis (CCSRA) to determine Δ14C and δ13C values of PAHs in PM2.5 samples for investigating biomass burning and fossil fuel source contributions to PAHs from one of the Southeastern Aerosol Research and Characterization (SEARCH) sites in North Birmingham (BHM), Alabama during winter (December 2004-February 2005) and summer (June-August 2005) by accelerator mass spectrometry. To compare our ambient samples to known sources, we collected and analyzed fenceline samples from the vicinity of a coke plant in BHM. As expected, PAHs from the coke plant fenceline samples had very low radiocarbon levels. Its Δ14C varied from −990 to −970‰, indicating that 97 to 99% were of fossil source. PAHs in the ambient PM2.5 had Δ14C from −968 to −911 ‰, indicating that 92–97% of PAHs were from fossil fuel combustion. These levels indicated the dominance of fossil sources of ambient PAHs. The radiocarbon level of ambient PAHs was higher in winter than in summer. Winter samples exhibited depleted δ13C value and enriched Δ14C value because of the increased contribution of PAHs from biomass burning source. However, biomass burning contributed more to heavier PAHs (modern source accounting for 6–8%) than lighter ones with a modern contribution of 3%.

•High atmospheric Pb concentration was observed in January 2013, Beijing.•4 types and 3 sources (combustion, iron industry and aging) of Pb were identified.•45% of the Pb particles were transported (much higher during haze episodes).Although leaded gasoline has been banned in some megacities in China since 1997 and nationally since 2000, atmospheric lead (Pb) pollution is still an important issue in China, as its concentration in megacities such as Beijing remains high. To measure the Pb concentration and identify sources of Pb-containing particles in Beijing during January 2013, both an online Single Particle Aerosol Mass Spectrometer (SPAMS) and offline filters analyzed by inductively coupled plasma-mass spectrometer (ICP-MS) were used at a monitoring site on the Peking University (PKU) campus. The average Pb concentration in PM2.5 was 370 ng/m3 in January 2013 and the highest daily concentration was as high as 1.3 μg/m3 during our sampling period. Based on the mass spectra from the SPAMS, these particles were classified into 4 major types, including NO3-rich (61%), ECOC-rich (18%), Fe-rich (14%), and SO4-rich (7%). Results from this study suggest that combustion processes and the iron/steel industry were the major primary sources of Pb in Beijing. On clean days, the importance of the primary combustion particle type (ECOC-rich) increased, while during severe haze episodes, Pb-containing particles mixed with secondary ions and Fe were dominant. Based on estimates from the CMAQ model, on average 45% of Pb in PM2.5 in urban Beijing was transported in January 2013, with a much higher percent transported during the haze episodes. The percentage of transported Pb increased with the concentration of Pb and PM2.5, indicating that emissions from the surrounding areas need to be controlled during high Pb episodes in Beijing in winter.Download high-res image (241KB)Download full-size image

•Single particle signatures from vehicle exhaust in a tunnel were performed and evaluated in ambient PM2.5.•The detection of PAHs in individual vehicle exhaust particles could be used for future source profiling experiments.•The major sources of ambient single particles was coal combustion, vehicle exhaust, and secondary ion.In order to accurately apportion the many distinct types of individual particles observed, it is necessary to characterize fingerprints of individual particles emitted directly from known sources. In this study, single particle mass spectral signatures from vehicle exhaust particles in a tunnel were performed. These data were used to evaluate particle signatures in a real-world PM2.5 apportionment study. The dominant chemical type originating from average positive and negative mass spectra for vehicle exhaust particles are EC species. Four distinct particle types describe the majority of particles emitted by vehicle exhaust particles in this tunnel. Each particle class is labeled according to the most significant chemical features in both average positive and negative mass spectral signatures, including ECOC, NaK, Metal and PAHs species. A single particle aerosol mass spectrometry (SPAMS) was also employed during the winter of 2013 in Guangzhou to determine both the size and chemical composition of individual atmospheric particles, with vacuum aerodynamic diameter (dva) in the size range of 0.2–2 μm. A total of 487,570 particles were chemically analyzed with positive and negative ion mass spectra and a large set of single particle mass spectra was collected and analyzed in order to identify the speciation. According to the typical tracer ions from different source types and classification by the ART-2a algorithm which uses source fingerprints for apportioning ambient particles, the major sources of single particles were simulated. Coal combustion, vehicle exhaust, and secondary ion were the most abundant particle sources, contributing 28.5%, 17.8%, and 18.2%, respectively. The fraction with vehicle exhaust species particles decreased slightly with particle size in the condensation mode particles.