Impact of Encouraging Vehicles to Refuel at Night on Ozone and Non-Methane Hydrocarbons (NMHCs): A Case Study in Ji’nan, China

Gasoline evaporation is a potential source of ambient non-methane hydrocarbons (NMHCs) during summer, and thus the policy of encouraging vehicles to refuel at night has been implemented to control ground-level ozone (O3) and NMHCs. In this study, NMHCs and trace gases were observed online at an urban site of Ji’nan during May–July in 2019 and 2020 to assess the impact of this policy. After the implementation of this policy, the average concentration of daily maximum 8 h moving average O3 decreased from 198 μg/m3 to 181 μg/m3. Meanwhile, the average mixing ratio of NMHCs decreased from 19.89 ppbv to 18.02 ppbv. Sources of NMHCs were then apportioned using the positive matrix factorization model. Four factors were resolved and identified, including vehicle exhaust, paint and solvents usage, gasoline evaporation, and biogenic emission. Relative contributions of these four sources were 52.5%, 20.6%, 18.3%, and 8.6%, respectively. After the implementation of this policy, relative contributions of gasoline evaporation in 1:00–4:00 increased from 20.2–22.7% to 25.4–28.2%, while those for 16:00–18:00 decreased from 16.8–18.7% to 13.9–15.7%. The non-linear relationship of O3 with NMHCs and NOx was investigated using a box model based on observations. Results suggest that O3 production was mainly controlled by NMHCs. Aromatics and alkenes were the key NMHC species in O3 formation. Furthermore, two scenarios of encouraging vehicles to refuel at night were designed to evaluate their impact on O3. The relative decreases of O3 peak concentrations were lower than 1%, indicating that this policy had a limited impact on O3 during the observation period.

Significant source of secondary aerosol: formation from gasoline evaporation emissions in the presence of SO₂ and NH₃

Gasoline evaporation emissions have become an important anthropogenic source of urban atmospheric VOCs and secondary organic aerosol (SOA). These emissions have a significant impact on regional air quality, especially in China where car ownership is growing rapidly. However, the contribution of evaporation emissions on the secondary aerosol (SA) is not clear in air pollution complex in which high concentration of SO2 and NH3 was present. In this study, the effects of SO2 and NH3 on SA formation from unburned gasoline vapors were investigated in a 30 m3 indoor smog chamber. It was found that increase in SO2 and NH3 concentrations could promote linearly the formation of SA, which could be enhanced by a factor of 1.6–2.6 and 2.0–2.5, respectively. Sulfate was most sensitive to the SO2 concentration, followed by organic aerosol, which was due not only to the well-known acid catalytic effect, but also related to the formation of organic sulfur-containing compounds. In the case of increasing NH3 concentration, ammonium nitrate increased more significantly than organic aerosol, and nitrogen-containing organics were also enhanced, as revealed by the results of positive matrix factorization (PMF) analysis. Meanwhile, new particle formation (NPF) and particle size growth were significantly enhanced in the presence of SO2 and NH3. This work indicates that gasoline evaporation emissions will be a significant source of SA, especially in the presence of high concentrations of SO2 and NH3. Meanwhile, these emissions might also be a potential source of sulfur- and nitrogen-containing organics. Our work provides a scientific basis for the synergistic emission reduction of secondary aerosol precursors, including NOx, SO2, NH3 and particularly VOCs, to mitigate PM pollution in China.

SOURCE APPORTIONMENT OF VOCS BY RECEPTOR MODELLING IN AN URBAN SITE IN HA NOI

Volatile organic compounds (VOCs) are atmospheric pollutants of concern because of the health effect including carcinogenic risk of some of their species and the contribution in the formation of tropospheric ozone. The levels of VOCs in Hanoi were demonstrated to be higher than neighboring countries by previous research. The ozone potential formation (OFP) of VOCs was also some folds higher than others. Among transportation sources, VOCs were proved to be mainly emitted from motorbikes. The contribution percentages of transportation and other sources such as industrial, biomass burning sources are still remained unknown. In this research we applied chemical mass balance (CMB) receptor modelling to determine VOCs source apportionment. One week VOCs observation data at Hanoi University of Science and Technology in June 2017 was applied for investigation. Fourteen VOC species among 55 of which were applied for CMB modelling. Transportation and biomass burning source profiles were developed by monitoring in this study. Four other source profiles, namely gasoline evaporation, industrial production, cooking and paint that were compiled or calculated from previous studies. The results showed that the main sources of VOCs were vehicular emission, biomass burning, and gasoline evaporation contributing 37 %, 21 % and 20 % for VOCs levels, respectively. Other sources contributed for the leftover. The results can support to initiate policy for future control of VOCs.

Source apportionment vs. emission inventories of non-methane hydrocarbons (NMHC) in an urban area of the Middle East: local and global perspectives

We applied the positive matrix factorization model to two large data sets collected during two intensive measurement campaigns (summer 2011 and winter 2012) at a sub-urban site in Beirut, Lebanon, in order to identify NMHC (non-methane hydrocarbons) sources and quantify their contribution to ambient levels. Six factors were identified in winter and five factors in summer. PMF-resolved source profiles were consistent with source profiles established by near-field measurements. The major sources were traffic-related emissions (combustion and gasoline evaporation) in winter and in summer accounting for 51 and 74 wt %, respectively, in agreement with the national emission inventory. The gasoline evaporation related to traffic source had a significant contribution regardless of the season (22 wt % in winter and 30 wt % in summer). The NMHC emissions from road transport are estimated from observations and PMF results, and compared to local and global emission inventories. The PMF analysis finds reasonable differences on emission rates, of 20–39 % higher than the national road transport inventory. However, global inventories (ACCMIP, EDGAR, MACCity) underestimate the emissions up to a factor of 10 for the transportation sector. When combining emission inventory to our results, there is strong evidence that control measures in Lebanon should be targeted on mitigating the NMHC emissions from the traffic-related sources. From a global perspective, an assessment of VOC (volatile organic compounds) anthropogenic emission inventories for the Middle East region as a whole seems necessary as these emissions could be much higher than expected at least from the road transport sector.

Source apportionment vs. emission inventories of non-methane hydrocarbons (NMHC) in an urban area of the Middle East: local and global perspectives

We applied the Positive Matrix Factorization model to two large datasets collected during two intensive measurement campaigns (summer 2011 and winter 2012) at a sub-urban site in Beirut, Lebanon, in order to identify NMHC sources and quantify their contribution to ambient levels. Six factors were identified in winter and five factors in summer. PMF-resolved source profiles were consistent with source profiles established by near-field measurements. The major sources were traffic-related emissions (combustion and gasoline evaporation) in winter and in summer accounting for 51 and 74 wt % respectively in agreement with the national emission inventory. The gasoline evaporation related to traffic source had a significant contribution regardless of the season (22 wt % in winter and 30 wt % in summer). The NMHC emissions from road transport are estimated from observations and PMF results, and compared to local and global emission inventories. The national road transport inventory shows lowest emissions than the ones from PMF but with a reasonable difference lower than 50 %. Global inventories show higher discrepancies with lower emissions up to a factor of 10 for the transportation sector. When combining emission inventory to our results, there is a strong evidence that control measures in Lebanon should be targeted on mitigating the NMHC emissions from the traffic-related sources. From a global perspective, an assessment of VOC anthropogenic emission inventories for the Middle East region as a whole seems necessary as these emissions could be much higher than expected at least from the road transport sector. Highlights: – PMF model was applied to identify major NMHC sources and their seasonal variation. – Gasoline evaporation accounts for more than 40 % both in winter and in summer. – NMHC urban emissions are dominated by traffic related sources in both seasons. – Agreement with the emission inventory regarding the relative contribution of the on-road mobile source but disagreement in terms of emission quantities suggesting an underestimation of the inventories.