Continuous measurements at the urban roadside in an Asian megacity by Aerosol Chemical Speciation Monitor (ACSM): particulate matter characteristics during fall and winter seasons in Hong Kong

Abstract

Abstract. Non-refractory submicron aerosol is characterized using an Aerosol Chemical Speciation Monitor (ACSM) in the fall and winter seasons of 2013 on the roadside in an Asian megacity environment in Hong Kong. Organic aerosol (OA), characterized by application of Positive Matrix Factorization (PMF), and sulfate are found to be dominant. Traffic-related organic aerosol shows good correlation with other vehicle-related species, and cooking aerosol displays clear mealtime concentration maxima and association with surface winds from restaurant areas. Contributions of individual species and OA factors to high NR-PM1 are analyzed for hourly data and daily data; while cooking emissions in OA contribute to high hourly concentrations, particularly during mealtimes, secondary organic aerosol components are responsible for episodic events and high day-to-day PM concentrations. Clean periods are either associated with precipitation, which reduces secondary OA with a lesser impact on primary organics, or clean oceanic air masses with reduced long-range transport and better dilution of local pollution. Haze events are connected with increases in contribution of secondary organic aerosol, from 30 to 50 % among total non-refractory organics, and the influence of continental air masses.

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

“…Higher EC concentrations were typically associated with rush hour traffic and confirm the local nature of EC and its relation to mainly on-road traffic Cheng et al, 2010;Huang et al, 2014;Louie et al, 2005). While earlier studies (samples dated pre-2005) reported EC concentrations in the range of 11-25 µg C m −3 in PM 2.5 at the open roadside (Louie et al, 2005;Cheng et al, 2010;Lee et al, 2006), more recent measurements (2012-2013) indicate a significant reduction in overall roadside EC burdens with concentrations ∼ 5 µg C m −3 Sun et al, 2016;. Vehicle-related concentrations at a roadside measurement site were estimated to ∼ 2 and ∼ 7 µg m −3 of OC and carbonaceous aerosol, respectively, in 2012, accounting for one-third of total OC in PM 2.5 and one-quarter of total PM 2.5 .…”

“…While most previous studies have evaluated traffic exhaust contributions in confined environments (tunnels), focal locations (e.g., bus terminus, taxi stand) or by plume chase, this work provides a quantitative estimation of vehicle exhaust related carbonaceous aerosol contributions and their relationship to traffic flow characteristics from ambient measurements in a more complex urban environment. We aim B. P. Lee et al: Evaluation of traffic exhaust contributions to ambient carbonaceous submicron PM to complement previous studies which only estimated overall traffic-related aerosol contributions from online and offline ECOC measurements at different time resolutions (from hourly to 24 h samples) (Louie et al, 2005;Huang et al, 2014) and online mass spectrometric methods (Sun et al, 2016;Lee et al, 2015) at the same location by combining resolved traffic-related organic aerosol concentrations from factor analysis of aerosol mass spectrometer (AMS) data, online EC measurements and traffic count data to gain an improved understanding of the influence of traffic composition on traffic-related submicron carbonaceous aerosol.…”

“…Additional data such as meteorological data (wind, temperature, relative humidity, solar irradiation), concentrations of VOCs, as well as trace gases (NO x , SO 2 and O 3 ) were available from the adjacent air quality monitoring site (AQMS) operated by the Environmental Protection Department (EPD) of the HKSAR Government on the same road divider island. Details on employed instrument model and sampling methodologies are available in other dedicated publications Environmental Protection Department, 2016;Sun et al, 2016). Elemental and organic carbon (EC, OC) were measured (semi-continuous thermooptical ECOC analyzer RT-3131, Sunset Inc., USA) at the AQMS at 1 h time resolution and at similar sampling height (∼ 2 m), employing a modified National Institute for Occupational Safety and Health (NIOSH) method 5040 protocol which has been described in a previous study .…”

“…The lack of a clear seasonal variation in OC / EC-derived traffic-related organics is due to the use of a fixed conversion factor directly dependent on ambient EC concentration, which did not exhibit a strong seasonal behavior and thus could not capture the same trends observed from the AMS measurements. The derivation of the OC / EC vehicle ratio is subject to further uncertainty due to the substantial influence of cooking-related organics at the site Sun et al, 2016) -i.e., traffic emissions may not be the dominant source of "local" organics at the site (Table 2), as well as the influence of background SOA, which is likely to persist even in time periods of low OC / EC ratios.…”

Air pollution in the Asia‐Pacific Region

“…The leading sources of ambient and household air pollution vary on the basis of regional economic development. In more developed urban regions, such as Beijing and Hong Kong, ambient air pollution is due largely to vehicle‐ and industry‐related emissions, whereas household air pollution results mostly from the infiltration of ambient PM. In less developed rural regions, levels of both ambient and household air pollution are driven mostly by biomass fuel burning .…”