Research progress of emission characteristics of polycyclic aromatic hydrocarbons and their derivatives of vehicle exhaust

Polycyclic aromatic hydrocarbons (PAHs) are a type of persistent organic pollutants with carcinogenic, teratogenic, and mutagenic effects. Moreover, the derivatives of PAHs, including nitro-PAHs (NPAHs) and oxygenated-PAHs (OPAHs), have strong oxidizing properties, and their mutagenicity and carcinogenic potential can reach 10 times and 100,000 times of the parent PAHs, respectively. Various epidemiological and toxicological studies have shown that PAHs and their derivatives are closely related to the occurrence and growth of many critical diseases. Therefore, PAHs have received immense attention in academics and is becoming a hot topic in scientific research. In recent years, a rapid increase in the number of motor vehicles has resulted in emissions from vehicles that have become one of the primary sources of PAHs and their atmospheric derivatives in almost all large and medium-sized cities. Based on the previous research, this review has summarized several standard sampling methods for vehicle exhaust, including bench experiment, vehicle-mounted experiment, tunnel experiment, and roadside experiment, and concluded the characteristics of PAHs and their derivatives from vehicle emissions (i.e., emission factor, gas-particle phase partitioning, source profiles, the influence of vehicle type, operating condition, and vehicle mileage). This review also provides scientific references for collecting sampling methods under various research demands by formulating emission reduction measures for motor vehicles. The oxygen content of ethanol–gasoline is higher than that of regular gasoline. The use of ethanol–gasoline can reduce many kinds of harmful substances in vehicle exhaust. At the same time, as straw is one of the raw materials of bioethanol, the promotion of ethanol gasoline for vehicles is also an important measure to solve the problem of burning agricultural waste such as straw and reduce the emission of pollutants. In this context, China plans to promote using vehicles with the ethanol–gasoline fuel nationwide in 2020 to alleviate the problem of pollution due to energy and motor vehicle emissions. However, there are certain differences in the properties between ethanol–gasoline and regular gasoline; hence, the impact of ethanol-blended gasoline on emissions from motor vehicles has attracted the attention of researchers. This paper reviewed the effect of ethanol-blended gasoline on the variation of pollution characteristics of PAHs and discussed their derivatives. Some useful suggestions for future research directions in this field are made, and scientific and reasonable references for the prevention and control measures of motor vehicle emission reduction are provided.