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Discussion papers | Copyright
https://doi.org/10.5194/acp-2018-387
© Author(s) 2018. This work is distributed under
the Creative Commons Attribution 4.0 License.

Research article 11 Jun 2018

Research article | 11 Jun 2018

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This discussion paper is a preprint. It is a manuscript under review for the journal Atmospheric Chemistry and Physics (ACP).

Vehicular volatile organic compounds (VOCs)-NOx-CO emissions in a tunnel study in northern China: emission factors, profiles, and source apportionment

Congbo Song1, Yan Liu1, Shida Sun1, Luna Sun1, Yanjie Zhang1, Chao Ma1, Jianfei Peng2, Qian Li1, Jinsheng Zhang1, Qili Dai1, Baoshuang Liu1, Peng Wang2, Yi Zhang1, Ting Wang1, Lin Wu1, Min Hu3, and Hongjun Mao1 Congbo Song et al.
  • 1Center for Urban Transport Emission Research & State Environmental Protection Key Laboratory of Urban Ambient Air Particulate Matter Pollution Prevention and Control, College of Environmental Science and Engineering, Nankai University, Tianjin, 300071, China
  • 2Zachry Department of Civil Engineering, Texas A and M University, College Station, TX, 77845, USA
  • 3Laboratory of Environmental Simulation and Pollution Control, College of Environmental Sciences and Engineering, Peking University, Beijing, 100871, China

Abstract. Vehicular emission is a key contributor to ambient volatile organic compounds (VOCs) and NOx in Chinese megacities. However, the information of real-world emission factors (EFs) for a typical urban fleet is still limited, hindering the development of a more reliable emission inventory in China. Based on a more-than-two-week (August 8–24, 2017) tunnel test in urban Tianjin in northern China, and on the use of a statistical regression model, the Positive Matrix Factorization (PMF) receptor model, and the Calculate Emissions from Road Transport (COPERT) IV model, characteristics of vehicular VOCs-NOx-CO emissions were analyzed systematically. The fleet-average EFs (pollutant: downslope, upslope, and overall in mgkm−1veh−1) were estimated respectively as follows: (NO: 61.92±72.46, 158.58±73.48, 97.52±69.84), (NO2: 16.52±11.49, 23.98±20.14, 15.86±9.38), (NOx: 79.45±78.43, 181.22±88.29, 116.56±77.61), and (CO: 269.96±342.38, 577.76±382.22, 344.67±250.01). The EFs of NO-NO2-NOx and CO from heavy-duty vehicles (or diesel vehicles) were differentiated from light-duty vehicles (or gasoline vehicles). The ratios (v/v) of NO2 to NOx in the primary vehicular exhaust were approximately 0.18±0.09, 0.10±0.22 and 0.10±0.05 for downslope, upslope, and the entire tunnel, respectively. The fleet-average EF of the 99-target non-methane VOCs (NMVOCs) was 40.56±12.18mgkm−1veh−1, lower than the previous studies in China. The BTEX (benzene, toluene, ethylbenzene, p-xylene, m-xylene and o-xylene) levels decreased by approximately 79% when emission standards increased from China I to China V. The source profiles of NMVOCs from the tailpipe and evaporative emissions were resolved by the PMF model. The evaporative emissions accounted for nearly one-half of the total vehicular VOC emissions, indicating that evaporative and tailpipe emissions contributed equally to VOC emissions. The relative contributions of evaporative NMVOC emissions to total vehicular NMVOC emissions are temperature-dependent with the average increasing ratio of 7.55%°C−1. The primary emission ratio (ER, m/m) of VOCs/NOx was approximately 2.04, suggesting that vehicular NOx and VOCs can be co-emitted with a proper ER. According to the vehicular ERs of VOCs/NOx in Tianjin (2000–2016) and China (2010–2030), as even more stringent emission standards are implemented in the future, the O3 chemical regimes were likely to be VOCs-limited (i.e., 8:1 threshold) for cities or regions where VOCs and NOx emissions are dominated by vehicular exhaust. Our study enriched the database on the fleet-average emission factors of on-road vehicles for emission inventory, air quality modeling, and health effects studies, provided implications for following O3 control in China from the view of primary emission, and highlighted the importance of further control of evaporative emissions.

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Short summary
Vehicular emission is a key contributor to ambient volatile organic compounds (VOCs) and NOx in Chinese megacities. Information on real-world emission factors (EFs) for a typical urban fleet is still limited. We found that improvement of fuel quality can significantly reduce feet-average EFs of VOCs (especially for BTEX). Our study provided implications for O3 control in China from the view of primary emission, and highlighted the importance of further control of evaporative emissions.
Vehicular emission is a key contributor to ambient volatile organic compounds (VOCs) and NOx in...
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