Measurement report: Distinct Emissions and Volatility Distribution of Intermediate Volatility Organic Compounds from on-road Chinese Gasoline Vehicle: Implication of High Secondary Organic Aerosol Formation Potential

Abstract

Abstract. In the present work, we performed chassis dynamometer experiments to investigate the emissions and secondary organic aerosol (SOA) formation potential of intermediate volatility organic compounds (IVOCs) from an on-road Chinese gasoline vehicle. High IVOCs emission factors (EFs) and distinct volatility distribution were recognized. The IVOCs EFs for the China V vehicle ranged from 12.1 to 226.3 mg · kg-fuel−1, with a median value of 83.7 mg · kg-fuel−1, which is higher than that from US vehicles. Besides, large discrepancy in volatility distribution and chemical composition of IVOCs from Chinese gasoline vehicle exhaust is discovered, with larger contributions of B14-B16 compounds and higher percentage of n-alkanes. Further we investigated the possible reasons that influence the IVOCs EFs and volatility distribution and found that fuel type, starting mode, operating cycles and acceleration rates could have an impact on the IVOCs EF. When using E10 (ethanol volume ratio of 10 %, v / v) as fuel, the IVOCs EF of the tested vehicle was lower than that using commercial China standard V fuel. Cold-start operation has higher IVOCs EF than hot-start operation. Chinese Light vehicles Test Cycle (CLTC) produced 70 % higher IVOCs than those from the World-wide harmonized Light-duty Test Cycle (WLTC). We found that vehicle emitted more IVOCs at lower acceleration rates, which leads to high EFs under CLTC. The only factor that may influence the volatility distribution and compound composition is the engine-aftertreatment system, which has compound and volatility selectivity in exhaust purification. These distinct characteristics in EFs and volatility may result in higher SOA formation potential in China. Using published yield data and surrogate equivalent method, we estimated SOA formation under different OA loading and NOx conditions. Results showed that under low and high NOx conditions at different OA loadings, IVOCs contributes more than 80% of the predicted SOA. Furthermore, we built up a parameterization method to simply estimate the vehicular SOA based on our bottom-up measurement of VOCs and IVOCs, which would provide another dimension of information when considering the vehicular contribution to the ambient OA. Our results indicate that vehicular IVOCs contribute significantly to SOA, implying that the importance of reducing IVOCs when making air pollution controlling policies in urban area of China.

Intermediate‐Volatility Organic Compounds Observed in a Coastal Megacity: Importance of Non‐Road Source Emissions

“…As shown in Table S3 in Supporting Information , concentrations of long‐chain alkanes in ambient air reported in previous studies (Xu et al., 2020; Zhao et al., 2014) were much lower than those observed in this study. The decreasing trend of n‐alkanes concentration with carbon numbers observed both in previous studies and in this study might be related to less higher‐carbon‐number alkanes in primary emission sources (Drozd et al., 2019; Huang et al., 2018; Qi et al., 2019; Tang et al., 2021; Zhao et al., 2015; Zhao, Nguyen, et al., 2016) or increasing OH reaction rate constants of n‐alkanes with carbon number (Table S4 in Supporting Information ).…”

“…Factor 3, with a significant amount of middle‐molecular‐weight alkanes, is considered as diesel‐related emission including on‐ and non‐road diesel engine emissions (Alam et al., 2019; Qi et al., 2019; Zhao et al., 2015). The dominance of n‐C 12 and n‐C 13 in factor 4 suggests that this factor is associated with gasoline exhaust (Fang, Huang, et al., 2021; Tang et al., 2021; Zhao, Nguyen, et al., 2016). Factor 2 is characterized by a high loading of PAHs, especially naphthalene.…”

“…Thus, as Figure 3 shows, although VOCs dominated (75.2%) the initial mass concentrations of SOA precursors, their contributions to estimated SOA were less significant than that of IVOCs. In fact, primary UCM IVOCs in typical sources could account for over 60% of the total primarily emitted IVOCs (Drozd et al., 2019; Huang et al., 2018; Lu et al., 2019; Qi et al., 2019; Tang et al., 2021; Zhao et al., 2015; Zhao, Nguyen, et al., 2016) (Figure S3 in Supporting Information ). Since the OH reaction rates and SOA yields of unspeciated cyclic compounds were similar or greater than those of n‐alkanes in the same bin and the residual primary UCM IVOCs largely consist of unspeciated cyclic compounds (Zhao et al., 2014), SOA production from residual primary UCM IVOCs could be roughly estimated as ∼9.41 μg m −3 with the assumption that OH reaction rates and SOA yields of the residual primary UCM IVOCs were the same as those of n‐alkanes in the same bin.…”

“…Ships are usually fueled with heavy fuel oil (HFO), of which the volatility of hydrocarbons is much lower than that of gasoline and diesel (Huang et al., 2018). Thus, higher‐molecular‐weight n‐alkanes, such as n‐C 20 ‐n‐C 22 , are relatively more abundant in ship exhaust, while gasoline combustion emits a substantial amount of lower‐molecular‐weight n‐alkanes, such as n‐C 12 and n‐C 13 (Drozd et al., 2019; Fang, Huang, et al., 2021; Tang et al., 2021; Zhao, Nguyen, et al., 2016), and more middle‐molecular‐weight n‐alkanes are present in diesel exhaust (Alam et al., 2019; Qi et al., 2019; Zhao et al., 2015) (Figure S6 in Supporting Information ). Figure 5 shows the source profile of the four factors resolved by the PMF model.…”

“…A previous study found similar concentration variation patterns of pristane (Pr), phytane (Ph), and primary IVOCs in Pasadena, suggesting that the major IVOC sources were likely petroleum‐related (Zhao et al., 2014). Recently, a number of studies have been conducted to measure IVOC emissions in typical combustion sources, such as biomass burning and on‐ and off‐road fossil‐fueled engines (Drozd et al., 2019; Fang, Huang, et al., 2021; Huang et al., 2018; Lu et al., 2019; Qi et al., 2019, 2021; Qian et al., 2021; Tang et al., 2021; Zhao et al., 2015; Zhao, Nguyen, et al., 2016). To date, however, the quantifiable results of different primary sources that contribute to ambient IVOCs are quite scarce.…”