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

• Main Authors: R. Tang, Q. Lu, S. Guo, H. Wang, K. Song, Y. Yu, R. Tan, K. Liu, R. Shen, S. Chen, L. Zeng, S. D. Jorga, Z. Zhang, W. Zhang, S. Shuai, A. L. Robinson
• Format: Article
• Language: English
• Published: Copernicus Publications 2021-02-01
• Series: Atmospheric Chemistry and Physics
• Online Access: https://acp.copernicus.org/articles/21/2569/2021/acp-21-2569-2021.pdf
• ISSN: 1680-7316; 1680-7324

<p>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 <span class="inline-formula">mg per kilogram fuel</span>, with a median value of 83.7 <span class="inline-formula">mg per kilogram fuel</span>, 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 <span class="inline-formula"><i>B</i>₁₄</span>–<span class="inline-formula"><i>B</i>₁₆</span> compounds (retention time bins corresponding to C<span class="inline-formula">₁₄</span>-C<span class="inline-formula">₁₆</span> <span class="inline-formula"><i>n</i></span>-alkanes) and a higher percentage of <span class="inline-formula"><i>n</i></span>-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 %, <span class="inline-formula"><math xmlns="http://www.w3.org/1998/Math/MathML" id="M9" display="inline" overflow="scroll" dspmath="mathml"><mrow><mi>v</mi><mo>/</mo><mi>v</mi></mrow></math><span><svg:svg xmlns:svg="http://www.w3.org/2000/svg" width="20pt" height="14pt" class="svg-formula" dspmath="mathimg" md5hash="96140f85aad72fddb5a8574659c38804"><svg:image xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="acp-21-2569-2021-ie00001.svg" width="20pt" height="14pt" src="acp-21-2569-2021-ie00001.png"/></svg:svg></span></span>) 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 <span class="inline-formula">0.07±0.01</span> and <span class="inline-formula">0.11±0.02</span>, 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.<span id="page2570"/> Using published yield data and a surrogate equivalent method, we estimated SOA formation under different OA (organic aerosol) loading and NO<span class="inline-formula">_<i>x</i></span> conditions. Results showed that under low- and high-NO<span class="inline-formula">_<i>x</i></span> 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.</p>