Tracking separate contributions of diesel and gasoline vehicles to roadside PM<sub>2.5</sub> through online monitoring of volatile organic compounds and PM<sub>2.5</sub> organic and elemental carbon: a 6-year study in Hong Kong

Abstract

Abstract. Vehicular emissions contribute a significant portion to fine particulate matter (PM2.5) air pollution in urban areas. Knowledge of the relative contribution of gasoline- versus diesel-powered vehicles is highly relevant for policymaking, and yet there is a lack of an effective observation-based method to determine this quantity, especially for its robust tracking over a period of years. In this work, we present an approach to track separate contributions of gasoline and diesel vehicles through the positive matrix factorization (PMF) analysis of online monitoring data measurable by relatively inexpensive analytical instruments. They are PM2.5 organic and elemental carbon (OC and EC), C2–C9 volatile organic compounds (VOCs) (e.g., pentanes, benzene, xylenes, etc.), and nitrogen oxide concentrations. The method was applied to monitoring data spanning more than 6 years between 2011 and 2017 in a roadside environment in Hong Kong. We found that diesel vehicles accounted for ∼70 %–90 % of the vehicular PM2.5 (PMvehicle) over the years and the remainder from gasoline vehicles. The diesel PMvehicle during truck- and bus-dominated periods showed declining trends simultaneous with control efforts targeted at diesel commercial vehicles and franchised buses in the intervening period. The combined PMvehicle from diesel and gasoline vehicles by PMF agrees well with an independent estimate by the EC-tracer method, both confirming PMvehicle contributed significantly to the PM2.5 in this urban environment (∼4–8 µg m−3, representing 30 %–60 % in summer and 10 %–20 % in winter). Our work shows that the long-term monitoring of roadside VOCs and PM2.5 OC and EC is effective for tracking gaseous and PM pollutants from different vehicle categories. This work also demonstrates the value of an evidence-based approach in support of effective control policy formulation.

Tracking Source Variations of Inhalation Cancer Risks and Ozone Formation Potential in Hong Kong over Two Decades (2000–2020) Using Toxic Air Pollutant Monitoring Data

“…The organic carbon (OC) and EC in PM 10 were determined with a thermal-optical transmittance method with the NIOSH 5040 temperature program . DPM was estimated as the sum of ambient EC and DPM-related organic matter: DPM = EC ambient + EC ambient × true[ normalOC normalEC true] DPM × 1.2 where [OC/EC] DPM is equal to 0.35, representing the OC-to-EC mass ratio in DPM determined from a previous local roadside study spanning 2011–2017, and the factor 1.2 is to account for the non-carbon fraction in vehicular organic matter. , We acknowledge that this method is associated with uncertainties arising from neglecting EC contribution from non-diesel sources and varying OC-to-EC ratio in DPM over time, resulting from the evolution of DPM control technologies, which have been discussed in our previous work and warrant further investigation …”

“…The benefits of such control efforts to air quality have been evidenced by various field measurement studies. 20,31 Benefiting from the sustained and ambitious local and regional air pollution control measures, a remarkable decrease in cancer risks equivalent to 191 cases per million was recorded between 2000−2004 and 2016−2020. The decrease was primarily driven by coal/biomass combustion showing an 80% reduction from 73 to 15 cases per million (including PAHs and metals/metalloids), solvent/gasoline with a 79% reduction from 67 to 14 cases per million, and freon/solvent/ gasoline/biogenic with a 61% reduction from 84 to 33 cases per million.…”

Source differences in the components and cytotoxicity of PM2.5 from automobile exhaust, coal combustion, and biomass burning contributing to urban aerosol toxicity

“…Some diesel vehicles showed higher EC emissions with age, so exhaust cleaning devices for them are suggested. In addition, the amounts of OC and EC in exhausts gradually decreased with the strengthened emission standards (Wong et al, 2020). In PM2.5 samples obtained from coal combustion (Figure S5), the TC contents of bituminous coals were significantly higher than that of honeycomb coals, anthracite coals, and industrial coals, because bituminous coals contain higher volatile fraction, which is composed of organic matter.…”

Source apportionment study on particulate air pollution in two high-altitude Bolivian cities: La Paz and El Alto

“…The low OC/EC ratios observed in high-altitude conditions are not surprising, as combustion processes are less efficient under low O 2 availability (Wang et al, 2013a). However, because of the very different conditions for combustion, the literature values of the ratio OC/EC (> 1 for gasoline and < 1 for diesel; Brito et al, 2013;Cheng et al, 2010Cheng et al, , 2021Wong et al, 2020;Yang et al, 2019) were not useful for identifying which of the traffic factors can be associated with gasoline-or diesel-powered vehicles, as both have OC/EC ratios close to 1 in the present study.…”