Size-resolved source apportionment of particulate matter from a megacity in northern China based on one-year measurement of inorganic and organic components.

This research apportioned size-resolved particulate matter (PM) contributions in a megacity in northern China based on a full year of measurements of both inorganic and organic markers. Ions, elements, carbon fractions, n-alkanes, polycyclic aromatic hydrocarbons (PAHs), hopanes and steranes in 9 p.m. size fractions were analyzed. High molecular weight PAHs concentrated in fine PM, while most other organic compounds showed two peaks. Both two-way and three-way receptor models were used for source apportionment of PM in different size ranges. The three-way receptor model gave a clearer separation of factors than the two-way model, because it uses a combination of chemical composition and size distributions, so that factors with similar composition but distinct size distributions (like more mature and less mature coal combustion) can be resolved. The three-way model resolved six primary and three secondary factors. Gasoline vehicles and coal and biomass combustion, nitrate and high relative humidity related secondary aerosol, and resuspended dust and diesel vehicles (exhaust and non-exhaust) are the top two contributors to pseudo-ultrafine (<0.43 µm), fine (0.43-2.1 µm) and coarse mode (>2.1 µm) PM, respectively. Mass concentration of PM from coal and biomass combustion, industrial emissions, and diesel vehicle sources showed a bimodal size distribution, but gasoline vehicles and resuspended dust exhibited a peak in the fine and coarse mode, separately. Mass concentration of sulphate, nitrate and secondary organic aerosol exhibited a bimodal distribution and were correlated with temperature, indicating strong photochemical processing and repartitioning. High relative humidity related secondary aerosol was strongly associated with size shifts of PM, NO3- and SO42- from the usual 0.43-0.65 µm to 1.1-2.1 µm. Our results demonstrated the dominance of primary combustion sources in the <0.43 µm particle mass, in contrast to that of secondary aerosol in fine particle mass, and dust in coarse particle mass in the Northern China megacity.

Size distributions of source-specific risks of atmospheric heavy metals: An advanced method to quantify source contributions to size-segregated respiratory exposure.

Heavy metals in size-segregated particulate matter (PM) were investigated in a Chinese megacity, and an advanced model was developed to quantify source-specific risks focusing on size-segregated respiratory exposure. Incremental lifetime cancer risk (ILCR) and non-cancer risk (hazard quotient: HQ) based on deposition concentrations of heavy metals displayed a peak at 4.7-5.8 µm. The percentage contributions to cancer risk were as follows: industrial emission (IE, 34%) > secondary and transport (ST, 29%) > resuspended dust (RD, 21%) > coal combustion (CC, 11%) > traffic emission (TE, 4%) during spring and summer (SS), and CC (31%) > ST (26%) > IE (21%) > RD (11%) ≈ TE (11%) during autumn and winter (AW). RD (41% of HQ during SS, 28% during AW) and IE (45% of HQ during SS, 35% during AW) dominated non-cancer risk. ILCR and HQ of CC were high at sizes 1.1-2.1 µm and 0.43-0.65 µm; those of RD were high at sizes > 3.3 µm; and those of IE were bimodal at fine (<2.1 µm) and coarse (>2.1 µm) sizes, respectively. Cancer risk was more susceptible to small particles than non-cancer risk, partly because higher ILCR was from CC, but higher HQ was attributed by RD.

[Construction and Evaluation on Size Resolved Source Apportionment Methods Based on Particle Size Distribution of Chemical Species].

The analysis of the sources of atmospheric particulate pollution can provide scientific support for the prevention and control of air pollution. Most particulate matter (PM) source analysis studies are based on the chemical composition of PM. In addition, particle size characteristics are also one of the important properties of PM. The accuracy of analytical results can be improved by analyzing the particle size characteristics of chemical components. In this study we aim to to solve the problem of insufficient utilization of component particle size information by using a the three-dimensional multi-particle size factor analysis model (ABB), where the particle size distribution of marked components is regarded as the constraint limit, and a multi-particle size source analytical model (SDABB) based on the characteristics of the components particle size distribution is constructed. The sensitivity of the SDABB model to the collinearity of the source spectrum and the similarity of the particle size distribution of the source contributions are investigated by evaluating the model through the simulation of the data set. The results showed that the ABB model was sensitive to the collinearity of the source spectrum and to the similarity of the particle size distribution of the source contributions. When particle size distribution rules were incorporated into the SDABB model, the effects of the two scenarios were significantly improved, that is, the SDABB model was able to better analyze collinear source spectrum and was insensitive to the similarity of the contribution particle size distribution.

Quantitatively analyzing effects of meteorology and PM2.5 sources on low visual distance.

Low visual distance (0 to 10 km), a common pollution phenomenon, is a severe threat to the productivity and life of human society in China. In this study, we used the Positive Matrix Factorization model coupled with the Generalized Additive Model (PMF-GAM) to quantitatively analyze the effect of the meteorology and source emissions on visual distance. The results show that the relative importance of predictor variables is humidity and SN (sulfate and secondary organic carbon (SOC) plus nitrate) (H&SN, 69.14%), vehicle exhaust (VE, 13.5%), crustal dust (CD, 7.28%), temperature (T, 4.71%), coal combustion (CC, 4.08%), wind speed (WS, 1.08%) and atmospheric pressure (AP, 0.21%). Furthermore, the visual distance is higher when the humidity is lower (<20%), and the humidity with SN shows clear synergy effects when the humidity is higher (>60%).

Transcriptomic Analysis of Musca domestica to Reveal Key Genes of the Prophenoloxidase-Activating System.

The proPO system regulates melanization in arthropods. However, the genes that are involved in the proPO system in housefly Musca domestica remain unclear. Thus, this study analyzed the combined transcriptome obtained from M. domestica larvae, pupae, and adults that were either normal or bacteria-challenged by an Escherichia coli and Staphylococcus aureus mixture. A total of 54,821,138 clean reads (4.93 Gb) were yielded by Illumina sequencing, which were de novo assembled into 89,842 unigenes. Of the 89,842 unigenes, based on a similarity search with known genes in other insects, 24 putative genes related to the proPO system were identified. Eight of the identified genes encoded for peptidoglycan recognition receptors, two encoded for prophenoloxidases, three encoded for prophenoloxidase-activating enzymes, and 11 encoded for serine proteinase inhibitors. The expression levels of these identified genes were investigated by qRT-PCR assay, which were consistent with expected activation process of the proPO system, and their activation functions were confirmed by the measurement of phenoloxidase activity in bacteria-infected larvae after proPO antibody blockage, suggesting these candidate genes might have potentially different roles in the activation of proPO system. Collectively, this study has provided the comprehensive transcriptomic data of an insect and some fundamental basis toward achieving understanding of the activation mechanisms and immune functions of the proPO system in M. domestica.

Molecular cloning and characterization of cecropin from the housefly (Musca domestica), and its expression in Escherichia coli.

A cDNA encoding housefly (Musca domestica) cecropin transcript was isolated from total RNA using RT-PCR, 3'RACE, and lambda gt11 cDNA library screening, and was expressed in Escherichia coli. This is the first report of a cecropin nucleotide and amino acid sequence in the housefly. The open reading frame of Md-Cec (189bp) encodes a precursor of 63 aa, which is comprised of a 23 aa signal peptide and a 40 aa mature peptide. In terms of amino acid sequence, Md-Cec shares a high degree of identity (74-82%) with those of some Diptera insects. Northern blot, RT-PCR and in situ hybridization analyses revealed that the prececropin was temporally expressed 5h after bacteria-challenge in larvae, and was induced in the fat body, epithelia of the body wall, and the epidermis of the midgut. The DNA fragment encoding mature Md-Cec was then subcloned into the pGEX-4T-1 expression vector and was highly expressed in E. coli BL21 with IPTG induction. The expressed proteins, fused to glutathion S-transferase, were purified by glutathion-Sepharose 4B affinity chromatography and cleaved with thrombin, followed by gel filtration chromatography. Recombinant Md-Cec exhibited antimicrobial activity against E. coli.