Vehicle -emitted fine particulate matter (PM 2.5 ) has been associated with significant health outcomes and environmental risks. This study estimates the contribution of traffic -related exhaust emissions (TREE) to observed PM 2.5 using a novel factorization framework. Specifically, co -measured nitrogen oxides (NO x ) concentrations served as a marker of vehicle -tailpipe emissions and were integrated into the optimization of a Non -negative Matrix Factorization (NMF) analysis to guide the factor extraction. The novel TREE-NMF approach was applied to long-term (2012 - 2019) PM 2.5 observations from air quality monitoring (AQM) stations in two urban areas. The extracted TREE factor was evaluated against co -measured black carbon (BC) and PM 2.5 species to which the TREE-NMF optimization was blind. The contribution of the TREE factor to the observed PM 2.5 concentrations at an AQM station from the first location showed close agreement ( R 2 = 0 .79) with monitored BC data. In the second location, a comparison of the extracted TREE factor with measurements at a nearby Surface PARTiculate mAtter Network (SPARTAN) station revealed moderate correlations with PM 2.5 species commonly associated with fuel combustion, and a good linear regression fit with measured equivalent BC concentrations. The estimated concentrations of the TREE factor at the second location accounted for 7 - 11 % of the observed PM 2.5 in the AQM stations. Moreover, analysis of specific days known to be characterized by little traffic emissions suggested that approximately 60 - 78 % of the traffic -related PM 2.5 concentrations could be attributed to particulate traffic -exhaust emissions. The methodology applied in this study holds great potential in areas with limited monitoring of PM 2.5 speciation, in particular BC, and its results could be valuable for both future environmental health research, regional radiative forcing estimates, and promulgation of tailored regulations for traffic -related air pollution abatement.

Particulate black carbon (BC) affects global warming by absorbing the solar radiation, by affecting cloud formation, and by decreasing ground albedo when deposited to snow or ice. BC has also a wide variety of adverse effects on human population health. In this article we reviewed the BC emission factors (EFs) of major anthropogenic sources, i.e. traffic (incl. marine and aviation), residential combustion, and energy production. We included BC EFs measured directly from individual sources and EFs derived from ambient measurements. Each source category was divided into sub-categories to find and demonstrate systematical trends, such as the potential influence of fuel, combustion technologies, and exhaust/flue gas cleaning systems on BC EFs. Our review highlights the importance of society level emission regulation in BC emission mitigation; a clear BC emission reduction was observed in ambient studies for road traffic as well as in direct emission measurements of diesel-powered individual vehicles. However, the BC emissions of gasoline vehicles were observed to be higher for vehicles with direct fuel injection techniques (gasoline direct injection) than for vehicles with port-fueled injection, indicating potentially negative trend in gasoline vehicle fleet BC EFs. In the case of shipping, a relatively clear correlation was seen between the engine size and BC EFs so that the fuel specific BC EFs of the largest engines were the lowest. Regarding the BC EFs from residential combustion, we observed large variation in EFs, indicating that fuel type and quality as well as combustion appliances significantly influence BC EFs. The largest data gaps were in EFs of large-scale energy production which can be seen crucial for estimating global radiative forcing potential of anthropogenic BC emissions. In addition, much more research is needed to improve global coverage of BC EFs. Furthermore, the use of existing data is complicated by different EF calculation methods, different units used in reporting and by variation of results due to different experimental setups and BC measurement methods. In general, the conducted review of BC EFs is seen to significantly improve the accuracy of future emission inventories and the evaluations of the climate, air quality, and health impacts of anthropogenic BC emissions.

Affected by global warming, permafrost thawing in Northeast China promotes issues including highway subgrade instability and settlement. The traditional design concept based on protecting permafrost is unsuitable for regional highway construction. Based on the design concept of allowing permafrost thawing and the thermodynamic characteristics of a block-stone layer structure, a new subgrade structure using a large block-stone layer to replace the permafrost layer in a foundation is proposed and has successfully been practiced in the Walagan-Xilinji of the Beijing-Mohe Highway to reduce subgrade settlement. To compare and study the improvement in the new structure on the subgrade stability, a coupling model of liquid water, vapor, heat and deformation is proposed to simulate the hydrothermal variation and deformation mechanism of different structures within 20 years of highway completion. The results show that the proposed block-stone structure can effectively reduce the permafrost degradation rate and liquid water content in the active layer to improve subgrade deformation. During the freezing period, when the water in the active layer under the subgrade slope and natural ground surface refreezes, two types of freezing forms, scattered ice crystals and continuous ice lenses, will form, which have different retardation coefficients for hydrothermal migration. These forms are discussed separately, and the subgrade deformation is corrected. From 2019 to 2039, the maximum cumulative settlement and the maximum transverse deformation of the replacement block-stone, breccia and gravel subgrades are -0.211 cm and +0.111 cm, -23.467 cm and -1.209 cm, and -33.793 cm and -2.207 cm, respectively. The replacement block-stone subgrade structure can not only reduce the cumulative settlement and frost heave but also reduce the transverse deformation and longitudinal cracks to effectively improve subgrade stability. However, both the vertical deformation and transverse deformation of the other two subgrades are too large, and the embankment fill layer will undergo transverse deformation in the opposite direction, which will cause sliding failure to the subgrades. Therefore, these two subgrade structures cannot be used in permafrost regions. The research results provide a reference for solving the settlement and deformation problems of subgrades in degraded permafrost regions and contribute to the development and application of complex numerical models related to water, heat and deformation in cold regions.

In this study, we categorized detailed mass-based emission factors (EFs) by age, calculated new estimates of fuel use, and developed spatially resolved emission inventories of constituents (PM2.5, black carbon [BC], and organic carbon [OC]) in the fine aerosol generated by the on-road transport sector in India. On a national level, this sector released an estimated 355 (104-607) Gg y(-1), 137 (47-227) Gg y(-1), and 106 (34-178) Gg y(-1) of PM2.5, BC, and OC, respectively, for the base year 2013, contributing nearly 7%, 17%, and 6% of the total emissions for each constituent. Although super-emitter vehicles comprised only 24% of the total traffic volume, they were responsible for 67% and 47% of the national PM2.5 and BC emissions, respectively, which indicates that eliminating these vehicles may rapidly reduce emissions from the on-road transport sector in India. To predict the direct radiative forcing (DRF) from BC emissions in this sector, we then input emission estimates for the carbonaceous aerosols into the Community Atmosphere Model (CAM5) global climate model and found a positive DRF of up to 6 W m(-2) at the top of the atmosphere (TOA) and a negative DRF of up to 10 W m(-2) at the surface, suggesting that as much as 16 W m(-2) of energy remains trapped within the atmosphere. With the rapid economic growth and continued urbanization, the transport sector in India is likely to further expand in the future and hence requires immediate attention in order to reduce the BC burden and improve air quality in the nation.