Contributions of vehicular carbonaceous aerosols to PM<sub>2.5</sub> in a roadside environment in Hong Kong

Abstract

Abstract. 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 onroad 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.

Evaluation of traffic exhaust contributions to ambient carbonaceous submicron particulate matter in an urban roadside environment in Hong Kong

“…Road traffic has been recognized as a major local emission source and subjected to various regulatory efforts over the years, such as a large-scale fuel switch of taxis to a virtually all-LPG fleet, partial conversion of minibuses to LPG engines, ex gratia incentive schemes for vehicle replacement or control device retrofitting and increased stringency in new-vehicle imports (Environmental Protection Department, 2013;Lyu et al, 2017;Ning et al, 2012). Characterization studies on particle-phase species associated with traffic emissions in Hong Kong have mainly focused on semi-continuous online and offline filter analysis with carbonaceous components (sum of elemental carbon and organic matter) typically constituting the bulk (45-70 %) of particulate mass in PM 2.5 at roadside sampling sites and up to 82 % in road tunnel environments Huang et al, 2014;Lee et al, 2006;Louie et al, 2005; Research Centre of Environmental Technology and Management, 2005). Among major primary and secondary aerosol sources of ambient particulate matter which were identified from speciated long-term filter samples (1998)(1999)(2000)(2001)(2002)(2003)(2004)(2005)(2006)(2007)(2008) of PM 2.5 by source apportionment analysis utilizing positive matrix factorization, vehicle emissions were shown to make substantial contributions: at general measurement sites (urban, rooftop), vehicle emissions accounted for 8-9 µg m −3 equivalent to 11-25 % of total PM 2.5 with lower fractions in the fall and winter seasons, primarily due to the masking in-fluence of regional and long-range transport.…”

Characteristics of Atmospheric PM2.5 in a Densely Populated City with Multi-Emission Sources

“…6. These carbonaceous constituents are important because they influence the potential for aerosols in terms of health impacts, climate change and visibility effect (Huang et al, 2014). The elemental carbon concentration ranged between 2.09-2.29 µg m , for spring, summer, autumn and winter respectively.…”

“…Additionally the secondary organic carbon, which can be formed from secondary atmospheric photochemical reactions was determined using the equation proposed by (Castro et al, 1999) which uses the minimum OC/EC ratio and EC tracer which is resistant to chemical reactions and a good indicator of anthropogenic pollutants Huang et al, 2014) .The equation used to estimate for SOC is as following Eq.5: SOC = OC Total -(OC/EC) min × EC (5) where SOC is the concentration of secondary OC (µg m -3 ), OC Total is the concentration of total OC (µg m Tseng et al, Aerosol and Air Quality Research, 16: 2145-21582154 the summer, 0.082-0.36 µg m -3 in the autumn and 0.04-0.037 µg m -3 in the winter, respectively. The corresponding fraction of SOC in the total OC (SOC/OC) was 4-9% in the spring, 1-11% in the summer, 3-12% in the autumn and 1-8% in the winter.…”

Source Apportionment of Submicron Particle Size Distribution and PM2.5 Composition during an Asian Dust Storm Period in Two Urban Atmospheres

“…The diesel dominant factor contributed the most to EC and approximately one-third to OC vehicle . The gasoline dominant factor contributed the least to EC but the most to OC vehicle (Huang et al, 2014). Thus, PC3 can be identified from vehicle emissions.…”