Measurement report: Distinct emissions and volatility distribution of intermediate-volatility organic compounds from on-road Chinese gasoline vehicles: 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 IVOC emission factors (EFs) and distinct volatility distribution were recognized. The IVOC EFs for the China V vehicle ranged from 12.1 to 226.3 mg per kilogram fuel, with a median value of 83.7 mg per kilogram fuel, which was higher than that from US vehicles. Besides, a large discrepancy in volatility distribution and chemical composition of IVOCs from Chinese gasoline vehicle exhaust was discovered, with larger contributions of B14–B16 compounds (retention time bins corresponding to C14-C16 n-alkanes) and a higher percentage of n-alkanes. Further we investigated the possible reasons that influence the IVOC EFs and volatility distribution and found that fuel type, starting mode, operating cycles and acceleration rates did have an impact on the IVOC EF. When using E10 (ethanol volume ratio of 10 %, v/v) as fuel, the IVOC EF of the tested vehicle was lower than that using commercial China standard V fuel. The average IVOC-to-THC (total hydrocarbon) ratios for gasoline-fueled and E10-fueled gasoline vehicles were 0.07±0.01 and 0.11±0.02, respectively. Cold-start operation had higher IVOC EFs than hot-start operation. The China Light-Duty Vehicle Test Cycle (CLTC) produced 70 % higher IVOCs than those from the Worldwide Harmonized Light Vehicles Test Cycle (WLTC). We found that the tested 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 a surrogate equivalent method, we estimated SOA formation under different OA (organic aerosol) loading and NOx conditions. Results showed that under low- and high-NOx conditions at different OA loadings, IVOCs contributed 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 (volatile organic compounds) 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 the importance of reducing IVOCs when making air pollution controlling policies in urban areas of China.

Measurement report: Emissions of intermediate-volatility organic compounds from vehicles under real-world driving conditions in an urban tunnel

“…3 shows the EFs and compositions of the vehicular IVOCs in each retention-time based bin (Table S1). Similar to previous studies (Zhao et al, 2015(Zhao et al, , 2016Huang et al, 2018;Qi et al, 2019;Tang et al, 2021), the unspeciated cyclic compounds dominated the IVOCs, accounting for 59.07 ± 1.06%, followed by unspeciated b-alkanes (25.27 ± 0.75%) and speciated IVOCs (15.66 ± 0.60%). The speciated IVOCs consist of n-alkanes, b-alkanes and PAHs.…”

“…The distribution of IVOCs in retention-time based bins presented a significant decreasing trend with bin numbers. Previous studies have reported that more than 50% of IVOCs concentrated in higher-volatility bins like B12, B13 and B14 in gasoline exhaust while much broader volatility distributions were found in diesel exhaust (Zhao et al, 2015(Zhao et al, , 2016Tang et al, 2021). The IVOCs in B12 measured in this study was also the most abundant as the GVs previously tested in the US (Fig.…”

“…2). A recent study revealed a significantly lower EFIVOCs of 83.7 mg kg -1 for a China V gasoline vehicle (Tang et al, 2021), implying that upgrading the emission standard could help reduce emissions of IVOCs from GVs, as China IV and China III GVs still share a much larger portion than the China V and VI ones in the on-road fleets (http://www.mee.gov.cn/). Fig.…”

“…Although previous chassis dynamometer tests used limited numbers of vehicles to characterize IVOCs emission (Zhao et al, 2015(Zhao et al, , 2016Tang et al, 2021), the results obtained from the tests were widely applied to recent models and emission inventories (Liu et al, 2017;Lu et al, 2018;Wu et al, 2019;Huang et al, 2020). However, driving conditions were recently found to significantly influence vehicular IVOCs emissions (Drozd et al, 2018;Tang et al, 2021), highlighting the importance of conducting on-road measurements of vehicle-emitted IVOCs under real-world driving condition, which could further narrow the uncertainty of vehicular IVOCs estimates in models and emission inventories. Tunnel test is a widely used method to characterize vehicle emissions in light of its advantage in capturing real-world emissions with a large number of driving vehicles.…”

“…However, emissions of IVOCs from mobile sources in China are much understudied. Only very recently, Tang et al (2021) tested emission of IVOCs from a China V light-duty gasoline vehicle. For this reason, IVOC emission factors derived from vehicle tests in the US have been used to update China's emission inventories with the inclusion of IVOCs (Liu et al, 2017).…”