科研之友
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摘要
Light gasoline vehicles are one of the most important emission sources of atmospheric volatile organic compounds (VOCs), and it is of great significance to analyze their emission characteristics for VOCs pollution control. In view of the lack of current research on the detailed description of vehicle VOCs emission characteristics under different driving conditions, this study constructed a combination of online and offline VOCs measurement system using a simple transient operating condition of chassis dynamometer operation (VMAS) and measured high-resolution emission characteristics of VOCs from 36 gasoline vehicles in Guangzhou. The study found that with the tightening of the national standard, VOCs emissions dropped by at least two orders of magnitude. Real-time observations indicated that the speed change, especially the acceleration phase, caused a significant increase in emissions. Heptane, butene, toluene, formaldehyde and methanol were the characteristic components. Correlations between components were generally 0.90~0.97. With the tightening of the national standard, the correlation decreased to 0.20~0.94, and alcohols had no or even negative correlation with other components. The distribution of the emission rate were concentrated in the shifting stage and much higher than the proportion of the idle and constant speed stages. Formaldehyde, acetaldehyde, acetone and other oxygenated VOCs maintained high and stable emissions at different speed change stages. This showed that over urban areas to reduce vehicle VOCs emissions, the long-term task is to reduce the frequent start-up and speed change caused by congestion or other factors, and to ensure smooth driving as far as possible. In this study, the comparison between the VOCs components identified by online testing and offline sampling was consistent. The use of online instruments makes up for the limitations of offline testing for identifying the real-time emission characteristics of VOCs.
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