Description:
Abstract. The Comprehensive Automobile Research System (CARS) is an open-sourcePython-based automobile emissions inventory model designed to efficientlyestimate high-quality emissions from motor vehicle emission sources. It canestimate air pollutant, greenhouse gas, and air toxin criteria atany spatial resolution based on the spatiotemporal resolutions of inputdatasets. The CARS is designed to utilize local vehicle activity data, suchas vehicle travel distance, road-link-level network geographic informationsystem (GIS) information, and vehicle-specific average speed by road type,to generate an automobile emissions inventory for policymakers,stakeholders, and the air quality modeling community. The CARS model adoptedthe European Environment Agency's on-road automobile emissionscalculation methodologies to estimate the hot exhaust, cold start, andevaporative emissions from on-road automobile sources. It can optionallyutilize average speed distribution (ASD) of all road types to reflect morerealistic vehicle speed variations. In addition, through utilizing high-resolutionroad GIS data, the CARS can estimate the road-link-level emissions toimprove the inventory's spatial resolution. When we compared the official2015 national mobile emissions from Korea's Clean Air Policy Support System(CAPSS) against the ones estimated by the CARS, there is a significantincrease in volatile organic compounds (VOCs) (33 %) and carbon monoxide(CO) (52 %) measured, with a slight increase in fine particulate matter(PM2.5) (15 %) emissions. Nitrogen oxide (NOx) and sulfur oxide(SOx) measurements are reduced by 24 % and 17 %, respectively, in the CARSestimates. The main differences are driven by different vehicle activitiesand the incorporation of road-specific ASD, which plays a critical role inhot exhaust emission estimates but was not implemented in Korea's CAPSSmobile emissions inventory. While 52 % of vehicles use gasoline fuel and35 % use diesel, gasoline vehicles only contribute 7.7 % of total NOxemissions, whereas diesel vehicles contribute 85.3 %. However, for VOC emissions,gasoline vehicles contribute 52.1 %, whereas diesel vehicles are limited to23 %. Diesel buses comprise only 0.3 % of vehicles and have thelargest contribution to NOx emissions (8.51 % of NOx total) pervehicle due to having longest daily vehicle kilometer travel (VKT). For VOCemissions, compressed natural gas (CNG) buses are the largest contributor at19.5 % of total VOC emissions. For primary PM2.5, more than 98.5 %is from diesel vehicles. The CARS model's in-depth analysis feature canassist government policymakers and stakeholders in developing the bestemission abatement strategies.