Characteristics of carbonyl emissions from light-duty gasoline vehicles and heavy-duty diesel trucks in China

Abstract

VOCs are important precursors to ozone and SOA in troposphere, greatly affecting the atmospheric chemistry. Among them, carbonyl compounds have earned more attention recently, due to their higher reactivity caused by the C=O group. Carbonyls can be generated by secondary oxidation but also can be primarily emitted. Vehicle emission can be the dominant anthropogenic source for the atmospheric carbonyls in urban area. However, most of the previous research on vehicle emissions only focused on regulated compounds (CO, HC, PM, NO_x, etc.). Only limited studies investigated the carbonyl emissions and only focused on a few species, lead to a lack of clarity on emission characteristics of carbonyls. In order to further understand the characteristics of vehicular carbonyl emissions in China, and to evaluate the impact of factors such as fuel, emission standards, etc., this study conducted chassis dynamometer measurements to measure the carbonyl emissions from 12 light-duty gasoline vehicles (LDGVs) and 20 heavy-duty diesel trucks (HDDTs) under different emission standards, measured emissions of 47 carbonyl species. The main conclusions are as follows: 1. The average emission factors (EFs) for the LDGV and HDDT fleets were 3.67 ± 1.00 mg/km and 7.85 ± 3.55 mg/km, respectively. The top three carbonyl compounds emitted from both vehicle types were formaldehyde, acetaldehyde, and acetone. Among them, the EF of formaldehyde in HDDT fleet can be notably high. 2. Along with the updating of the emission standard, the carbonyl EFs did not show a complete decrease trend. The highest EF in LDGVs was observed in China IV fleet, then decreased to China VI fleets. China V fleet showed the highest EF in HDDTs. Although both types of vehicles showed a decreasing trend in their latest emission standards, the reasons behind are different. 3. Carbonyl emissions fractions were increasing comparing to the HCs with the updating of emission standards in both LDGVs and HDDTs. 4. Reformulated gasoline (RFG) did not reduce the emission of carbonyl compounds compared to the conventional gasoline in LDGVs. Moreover, the combination of RFG with China VI fleet could result in a substantial increase in carbonyl emissions. 5. The annual vehicular carbonyl emission of HDDTs is only one-third of LDGVs, although HDDTs have higher EFs. When it comes to reducing annual vehicular carbonyl emissions, LDGVs are more crucial.

Date of Award	2024
Original language	English
Awarding Institution	The Hong Kong University of Science and Technology
Supervisor	Zhe WANG (Supervisor)