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Fine particulate matter (PM 2.5) significantly impacts global air quality and human health due to its smaller particle size and larger specific surface area. Nitrogen and carbon aerosols, as the main components of PM 2.5 , play key roles in air pollution. This study identified the sources and seasonal variation of nitrogen and carbon aerosols in PM 2.5 in typical cities of Zhejiang. The annual average PM 2.5 concentrations of Hangzhou (HZ), Ningbo (NB), and Huzhou (HUZ) were 39.8 ± 19.1 μg m−‍3, 40.0 ± 21.5 μg m−3, and 50.1 ± 22.6 μg m−3, respectively, which exceeded the Chinese air quality limit of 35.0 μg m−3. The results showed that the concentrations of nitrogen aerosols (NO 3 − and NH 4 +) in water-soluble inorganic ions were higher at 9.6 ± 4.6 μg m−3, 9.0 ± 4.5 μg m−3 and 11.5 ± 5.4 μg m−3 in HZ, NB and HUZ, respectively, especially in winter, accounting for over 60% of the total. The annual average δ15N values of PM 2.5 were 6.2 ± 1.9‰, 6.4 ± 2.2‰ and 6.7 ± 1.9‰ in HZ, NB and HZ, respectively; the δ15N values in winter were relatively low. A Bayesian isotopic mixing model was employed to analyse the sources of nitrogen aerosols in winter; the results showed that nitrogen concentration was mainly affected by NH 3 and NO X emitted by motor vehicle exhaust, coal combustion, biomass combustion, biogenic soil emissions, animal wastes and ocean evaporation (NB). In addition, the carbon component analysis of PM 2.5 showed that the annual average mass concentration of TC accounted for 18.7%, 16.4% and 20.1% of PM 2.5 in HZ, HUZ and NB, respectively. The same isotope model was used to analyse the sources of carbon aerosols; the results showed that carbon aerosols were mainly affected by the sources of motor vehicle exhaust, coal combustion, biomass combustion and dust. In the PM 2.5 in Zhejiang, the most contributory sources of nitrogenous aerosols and carbon aerosols were motor vehicle exhaust sources. [Display omitted] • The fractionation coefficients for nitrogen aerosol conversions are different in Hangzhou, Ningbo, and Huzhou. • The NO X and NH 3 sources of aerosol NO 3 − and NH 4 + in Hangzhou, Ningbo, and Huzhou were identified. • The stable carbon and nitrogen isotope values of dust sources in Hangzhou, Ningbo and Huzhou are significantly different. • The main sources of carbon aerosol are motor vehicle exhaust in Hangzhou, Ningbo and Huzhou. [ABSTRACT FROM AUTHOR]

Nitrogen amendment is known to effectively enhance the bioremediation of hydrocarbon-contaminated soil, but the nitrogen metabolism in this process is not well understood. To unravel the nitrogen metabolic pathway(s) of diesel contaminated soil, six types of nitrogen sources were added to the diesel contaminated soil. Changes in microbial community and soil enzyme genes were investigated by metagenomics analysis and chemical analysis through a 30-day incubation study. The results showed that ammonium based nitrogen sources significantly accelerated the degradation of total petroleum hydrocarbon (TPH) (79–81%) compared to the control treatment (38%) and other non-ammonium based nitrogen amendments (43–57%). Different types of nitrogen sources could dramatically change the microbial community structure and soil enzyme gene abundance. Proteobacteria and Actinobacteria were identified as the two dominant phyla in the remediation of diesel contaminated soil. Metagenomics analysis revealed that the preferred metabolic pathway of nitrogen was from ammonium to glutamate via glutamine, and the enzymes governing this transformation were glutamine synthetase and glutamate synthetase; while in nitrate based amendment, the conversion from nitrite to ammonium was restrained by the low abundance of nitrite reductase enzyme and therefore retarded the TPH degradation rate. It is concluded that during the process of nitrogen enhanced bioremediation, the most efficient nitrogen cycling direction was from ammonium to glutamine, then to glutamate, and finally joined with carbon metabolism after transforming to 2-oxoglutarate. • Ammonium is the preferred nitrogen source in enhancing the biodegradation of diesel. • Proteobacteria and Actinobacteria dominated the diesel biodegradation process. • Glutamine synthetase and glutamate synthetase were the key enzymes in nitrogen cycle. • DNRA and denitrification were not the governing pathway of nitrite transformation. • The dominant nitrogen cycling direction was from ammonium to glutamate via glutamine. [ABSTRACT FROM AUTHOR]