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Abstract. Vehicular emissions contribute a significant portion tofine particulate matter (PM2.5) air pollution in urban areas. Knowledgeof the relative contribution of gasoline- versus diesel-powered vehicles ishighly relevant for policymaking, and yet there is a lack of an effective observation-basedmethod to determine this quantity, especially for its robust tracking over aperiod of years. In this work, we present an approach to track separatecontributions of gasoline and diesel vehicles through the positive matrixfactorization (PMF) analysis of online monitoring data measurable byrelatively inexpensive analytical instruments. They are PM2.5 organicand elemental carbon (OC and EC), C2–C9 volatile organiccompounds (VOCs) (e.g., pentanes, benzene, xylenes, etc.), and nitrogenoxide concentrations. The method was applied to monitoring data spanningmore than 6 years between 2011 and 2017 in a roadside environment in Hong Kong.We found that diesel vehicles accounted for ∼70 %–90 % ofthe vehicular PM2.5 (PMvehicle) over the years and the remainderfrom gasoline vehicles. The diesel PMvehicle during truck- andbus-dominated periods showed declining trends simultaneous with controlefforts targeted at diesel commercial vehicles and franchised buses in theintervening period. The combined PMvehicle from diesel and gasolinevehicles by PMF agrees well with an independent estimate by the EC-tracermethod, both confirming PMvehicle contributed significantly to thePM2.5 in this urban environment (∼4–8 µg m−3, representing 30 %–60 % in summer and 10 %–20 % in winter). Ourwork shows that the long-term monitoring of roadside VOCs and PM2.5 OC andEC is effective for tracking gaseous and PM pollutants from differentvehicle categories. This work also demonstrates the value of anevidence-based approach in support of effective control policy formulation.

atmospheric chemistry and physics

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