Index Geophysics

Contributions of vehicular carbonaceous aerosols to PM2.5 in a roadside environment in Hong Kong

Hourly measurements of elemental carbon (EC) and organic carbon (OC) were made at Mong Kok, a roadside air quality monitoring station in Hong Kong, for a year, from May 2011 to April 2012. The monthly average EC concentrations were 3.8–4.9 μg C m⁻³, accounting for 9.2–17.7% of the PM_2.5 mass (21.5–49.7 μg m⁻³). The EC concentrations showed little seasonal variation and peaked twice daily, coinciding with the traffic rush hours of a day. Strong correlations were found between EC and NO_x concentrations, especially during the rush hours in the morning, confirming vehicular emissions as the dominant source of EC at this site. The analysis by means of the minimum OC / EC ratio approach to determine the OC / EC ratio representative of primary vehicular emissions yields a value of 0.5 for (OC / EC)_vehicle. By applying the derived (OC / EC)_vehicle ratio to the data set, the monthly average vehicle-related OC was estimated to account for 17–64% of the measured OC throughout the year. Vehicle-related OC was also estimated using receptor modeling of a combined data set of hourly NO_x, OC, EC and volatile organic compounds characteristic of different types of vehicular emissions. The OC_vehicle estimations by the two different approaches were in good agreement. When both EC and vehicle-derived organic matter (OM) (assuming an OM-to-OC ratio of 1.4) are considered, vehicular carbonaceous aerosols contributed ~ 7.3 μg m⁻³ to PM_2.5, accounting for ~ 20% of PM_2.5 mass (38.3 μg m⁻³) during winter, when Hong Kong received significant influence of air pollutants transported from outside, and ~ 30% of PM_2.5 mass (28.2 μg m⁻³) during summertime, when local emission sources were dominant. A reduction of 3.8 μg m⁻³ in vehicular carbonaceous aerosols was estimated during 07:00–11:00 (i.e., rush hours on weekdays) on Sundays and public holidays. This could mainly be attributed to less on-road public transportation (e.g., diesel-powered buses) in comparison with non-holidays. These multiple lines of evidence confirm local vehicular emissions as an important source of PM_2.5 in an urban roadside environment and suggest the importance of vehicular emission control in reducing exposure to PM_2.5 in busy roadside environments.

Huang, X. H. H.

Bian, Q. J.

Louie, P. K. K.

Yu, J. Z.

2018-09-14

Text

application/pdf

10.5194/acp-14-9279-2014

https://acp.copernicus.org/articles/14/9279/2014/

eISSN: 1680-7324

eng