Emission Characteristics and Atmospheric Chemical Reactivity of Volatile Organic Compounds(VOCs) in Automobile Repair Industry

Abstract

Volatile organic compounds (VOCs) emitted by the automobile repair industry are an important source of ozone precursors. However, the current reduction policy generally focuses on the emissions of VOCs, without considering their chemical reactivity. Based on an investigation of the development status of China's automobile repair industry, this study analyzes VOCs emission nodes in different sections of automobile repair enterprises. The amount and VOCs content of paint in each section was determined, and a material balance algorithm was used for sections with different VOCs quantities and compositions to analyze the emission characteristics of exhaust VOCs. The atmospheric reactivity of VOCs components was evaluated by calculating ozone generation potential (OFP). The results show that VOCs components produced by automobile repair paint are mainly benzene homologues, with butyl acetate and xylene the highest. Varnish is the largest contributor to VOCs emissions in automobile repair industries (92%), due to its high VOCs content and high dosage. The VOCs content of solvent-based coatings (22%) is higher than that of water-based coatings (3%). The application of water-based coatings leads to a remarkable reduction in VOCs emissions in automobile repair industries. A total of 49 VOCs components have been detected in gas from exhaust cylinders, with the top 10 VOCs components accounting for 97.9% of the total emissions. The main pollutants are aromatic hydrocarbons (10 types, 30.90%-69.30%), and OVOC (12 types) and halogenated hydrocarbons (22 types) were the second-highest contributors, with contribution rates of 8.82%-43.71% and 2.40%-25.00%, respectively. Aromatic hydrocarbon is the largest VOCs component emitted by automobile repair industries, but the main types of VOCs vary greatly in different studies. VOCs discharged by automobile repair industries have an average OFP value of 194.04 mg ·m-3 and an average SR value of 3.37 g ·g-1. The m/p-xylene component contributes the most to OFP (70.24%) and is the preferred pollutant in automobile repair industry. Aromatic hydrocarbons contribute a maximum of 99.29% to the OFP value and are also the most chemically reactive component. Although esters account for a large proportion of VOCs, their contribution to OFP is relatively low. Therefore, the automobile repair industry should focus on controlling the emission of aromatic hydrocarbons.