Oxidation and sources of atmospheric NOx during winter in Beijing based on δ18O-δ15N space of particulate nitrate.

The determination of both stable nitrogen (δ15N-NO3-) and stable oxygen (δ18O-NO3-) isotopic signatures of nitrate in PM2.5 has shown potential for an approach of assessing the sources and oxidation pathways of atmospheric NOx (NO+NO2). In the present study, daily PM2.5 samples were collected in the megacity of Beijing, China during the winter of 2017-2018, and this new approach was used to reveal the origin and oxidation pathways of atmospheric NOx. Specifically, the potential of field δ15N-NO3- signatures for determining the NOx oxidation chemistry was explored. Positive correlations between δ18O-NO3- and δ15N-NO3- were observed (with R2 between 0.51 and 0.66, p < 0.01), and the underlying environmental significance was discussed. The results showed that the pathway-specific contributions to NO3- formation were approximately 45.3% from the OH pathway, 46.5% from N2O5 hydrolysis, and 8.2% from the NO3+HC channel based on the δ18O-δ15N space of NO3-. The overall nitrogen isotopic fractionation factor (εN) from NOx to NO3- on a daily scale, under winter conditions, was approximately +16.1‰±1.8‰ (consistent with previous reports). Two independent approaches were used to simulate the daily and monthly ambient NOx mixtures (δ15N-NOx), respectively. Results indicated that the monthly mean values of δ15N-NOx compared well based on the two approaches, with values of -5.5‰ ± 2.6‰, -2.7‰ ± 1.9‰, and -3.2‰ ± 2.2‰ for November, December, and January (2017-2018), respectively. The uncertainty was in the order of 5%, 5‰ and 5.2‰ for the pathway-specific contributions, the εN, and δ15N-NOx, respectively. Results also indicated that vehicular exhaust was the key contributor to the wintertime atmospheric NOx in Beijing (2017-2018). Our advanced isotopic perspective will support the future assessment of the origin and oxidation of urban atmospheric NOx.

Emission factors of volatile organic compounds (VOCs) based on the detailed vehicle classification in a tunnel study.

In order to obtain VOCs emission characteristics and emission factors from vehicle, a tunnel experiment was conducted in the Fu Gui Mountain Tunnel in Nanjing, China. The tunnel is located in the middle of city, with total length of 480m and speed limit of 50km/h. The studied vehicle fleet was composed of 87% light duty vehicles and 13% heavy duty vehicles (liquefied natural gas bus, LNGB). The emerging radio frequency identification (RFID) technology was used to divide fine vehicles type including China I, China II, China III, China IV, China V and LNGB. Ambient air samples (4-h averages) were collected inside the tunnel using 3.2L stainless-steel canisters. Samples collected in the canisters were analyzed for 97 individual VOCs using high-resolution GC-MS in the laboratory. The average tunnel emission factor for the collective light-duty vehicles was 160.79±65.94mg/(km∗veh), and for the China I, China II, China III, China IV and China V vehicles, it was 632.07±259.44, 450.35±184.85, 205.42±84.32, 118.51±48.65, and 110.61±45.4mg/(km∗veh), respectively. The average emission factor for heavy-duty vehicles was 358.02±124.86mg/(km∗veh). Ethane, isopentane, propane, ethylene, toluene, propylene and 2,3-dimethylbutane were the most common VOC species in vehicle emissions. The total O3 formation potential was 373.88mg∗O3/(km∗veh) in the tunnel. Ethylene, propylene, m/p-xylene, toluene, and isopentane were the largest contributors to O3 production. Compared with previous studies, fuel quality increased from China II-FQ to China IV-FQ levels, while the BTEX emission levels exhibited a decreasing trend.

[Characteristics and Health Risk Assessment of Metallic Elements in PM2.5 Fraction of Road Dust].

In order to analyze and compare the pollution characteristics and risks to human health of metallic elements in the PM2.5 fraction of urban road dust (RD) and park road dust (PRD), particles smaller than 2.5 µm were suspended to filters by a re-suspension system and concentrations of Na, Mg, Al, Fe, Cu, Mn, Ni, Sb, Zn, Cd, and Pb were quantified. Results showed that the average concentrations of Cu and Sb in RD were 626 mg·kg-1 and 23 mg·kg-1, significantly higher than that in PRD (274 mg·kg-1 and 11 mg·kg-1). This indicated that the elemental composition of RD was influenced by non-exhaust emissions. The geoaccumulation Index (Igeo) of each detected element showed that samples were strongly to extremely contaminated by Cd (4 < Igeo < 5), moderately to strongly contaminated by Cu, Sb, Zn, and Pb (2 < Igeo < 4), and uncontaminated to moderately contaminated by Ni and Mn (Igeo < 1). The hazard index (HI) values of Sb, Pb, Cu, Ni, Zn, and Cd were less than 1 and the incremental lifetime cancer risk (ILCR) values of Ni and Cd were less than 10-6, indicating that these elements of RD and PRD are not associated with any cancer risks or non-cancer health risks.

[Characteristics of Particulate Matter and Carbonaceous Species in Ambient Air at Different Air Quality Levels].

This study describes the characteristics of particulate matter and carbonaceous species at different air quality levels. The concentrations of PM10, PM2.5, PM1, and carbonaceous species in PM2.5 were monitored on-line in Langfang City on March 1-22, 2016. The PM10, PM2.5, and PM1 concentrations were 204.1 µg·m-3, 107.9 µg·m-3, and 87.8 µg·m-3, respectively. Diurnal variations in particulate matter concentrations showed a bimodal distribution. In general, the mass concentrations of particulate matter and carbonaceous species (OC, EC, SOC, and POC) and the ratios of PM1/PM10 and PM2.5/PM10 were lower on better air quality periods. However, the mass concentration of PM10 was the highest on moderately polluted times. The ratios of PM1/PM10 and PM2.5/PM10 reached minimum values on moderately polluted times.The mass concentration of OC was slightly lower in moderately polluted periods than slightly polluted times; it was significantly lower in moderately polluted periods compared to severely polluted time periods. Hourly concentrations of OC and EC were lower between the hours of 13:00 and 23:00 compared to slightly polluted and severely polluted periods. The proportion of PM2.5 and PM1 decreased in moderately polluted time periods, consistent with the corresponding primary pollutants. Besides, the value of OC/EC was larger than 2.0. The concentrations of SOC and POC estimated using the minimum OC/EC ratio were 12.2 µg·m-3 and 5.0 µg·m-3, respectively.

[Water-soluble Inorganic Ions in the Road Ambient Atmospheric Particles of Tianjin].

Atmospheric particles, especially water-soluble inorganic ions are hazardous to human body. Motor vehicle exhaust is the greatest contributor to atmosphere pollution in Tianjin. In order to explore the emission characteristics of different road types, PM2.5 and PM10 from four types of roads were sampled and analyzed by water-soluble ions component analysis and Pearson correlation analysis during the period of April to May, 2015 to discover the ratio of PM2.5 to PM10 and the major pollutants. The results showed that water-soluble inorganic ions mainly existed in fine particles varying with different road types, which mainly came from secondary pollution. The quantities of secondary ions in PM2.5 were twice as high as that in PM10, which were the key components of the water-soluble inorganic ions. This was probably due to the increase of automobiles and their emissions, as well as the transmission and spreading of pollutants in the surroundings. Furthermore, water-soluble inorganic ions might exist in the forms of NaNO3, NH4Cl, NH4NO3, (NH4)2SO4, KCl, KNO3, K2SO4, MgCl2, CaCl2, etc. K+, Mg2+, Na+and Ca2+ showed high homology and the contributors of PM2.5 and PM10 were mainly the mixture of combustion and secondary pollutants, then followed by the mixture of re-suspended dust and traffic source.