Hong Kong vehicle emission changes from 2003 to 2015 in the Shing Mun Tunnel

• Published in: Aerosol science and technology Vol. 52; no. 10; pp. 1085 - 1098
• Main Authors: Wang, Xiaoliang, Ho, Kin-Fai, Chow, Judith C., Kohl, Steven D., Chan, Chi Sing, Cui, Long, Lee, Shun-cheng Frank, Chen, Lung-Wen Antony, Ho, Steven Sai Hang, Cheng, Yan, Watson, John G.
• Format: Journal Article
• Language: English
• Published: New York Taylor & Francis 03-10-2018; Taylor & Francis Ltd
• Subjects: Aerosol research; Ammonia; Carbon monoxide; Combustion products; Emission analysis; Emission measurements; Emissions control; Exhaust emissions; Exhaust pipes; Motor vehicles; Nitrogen dioxide; Nitrogen oxides; Organic matter; Oxides; Particulate matter; Paul Ziemann; Photochemicals; Sulfates; Sulfur; Sulfur dioxide; Vehicle emissions; Hong Kong China
• ISSN: 0278-6826; 1521-7388
• DOI: 10.1080/02786826.2018.1456650

This study characterized motor vehicle emission rates and compositions in Hong Kong's Shing Mun tunnel (SMT) during 2015 and compared them to similar measurements from the same tunnel in 2003. Average PM
2.5
concentrations in the SMT decreased by ∼70% from 229.1 ± 22.1 µg/m
3
in 2003 to 74.2 ± 2.1 µg/m
3
in 2015. Both PM
2.5
and sulfur dioxide (SO
2
) emission factors (EF
D
) were reduced by ∼80% and total non-methane (NMHC) hydrocarbons EF
D
were reduced by 44%. These reductions are consistent with long-term trends of roadside ambient concentrations and emission inventory estimates, indicating the effectiveness of emission control measures. EF
D
changes between 2003 and 2015 were not statistically significant for carbon monoxide (CO), ammonia (NH
3
), and nitrogen oxides (NO
x
). Tunnel nitrogen dioxide (NO
2
) concentrations and NO
2
/NO
x
volume ratios increased, indicating an increased NO
2
fraction in the primary vehicle exhaust emissions. Elemental carbon (EC) and organic matter (OM) were the most abundant PM
2.5
constituents, with EC and OM, respectively, contributing to 51 and 31% of PM
2.5
in 2003, and 35 and 28% of PM
2.5
in 2015. Average EC and OM EF
D
decreased by ∼80% from 2003 to 2015. The sulfate EF
D
decreased to a lesser degree (55%) and its contribution to PM
2.5
increased from 10% in 2003 to 18% in 2015, due to influences from ambient background sulfate concentrations. The contribution of geological materials to PM
2.5
increased from 2% in 2003 to 5% in 2015, signifying the importance of non-tailpipe emissions.
© 2018 American Association for Aerosol Research