Abstract
Traffic-related emissions were measured at a heavy-traffic roadside in Xi’an at the end of April, 2008 to survey the exposure levels of freshly emitted carbon monoxide (CO), mass and chemical composition (OC, EC, inorganic ions, and PAHs) of PM 10, and ozone (O3). In general, high levels of mass concentration and chemical species in PM10 were observed during daily heavy traffic periods (morning, noon, and evening traffic rush hours), especially in the morning traffic rush hour. OC and EC accounted for 9.3% and 3.0% of PM10 mass, respectively, and the ratios of OC/EC were constant during the heavy traffic periods (with a mean value of 3.2). Water-soluble ions constituted 14.0% of PM10 and the dominant ionic species were Ca 2+ , SO4 2- , and NO3 - in the roadside samples. Re-suspended road dust constituted a large fraction of PM10, causing the PM10 samples to become more alkaline. The concentrations of 12 prior-controlled PAHs revealed the potential high health risk of this roadside area in Xi’an. The diurnal variation in CO and O3 exhibited a different trend, which indicated that CO level was largely influenced by the instantaneous emission of vehicles while O3 was closely associated with the overall traffic conditions and meteorological status.
Highlights
In the last decade, the number of motor vehicles used has increased, and their emissions have become the dominant contributors to air pollution
The highest PM10 level occurred during the morning rush period and may have been largely due to stable atmospheric conditions, whereas the lower concentration at noon primarily depended on an increasing trend in mixing layer height which reached a maximum at about 14:00 local time
This study demonstrated that the source profile of polycyclic aromatic hydrocarbons (PAHs) from gasoline vehicles in Xi’an was similar with that observed in other countries, and these fingerprints can be reliably used in China
Summary
The number of motor vehicles used has increased, and their emissions have become the dominant contributors to air pollution. Traffic-related emissions, such as particulate matter (PM), organic carbon (OC), elemental carbon (EC), polycyclic aromatic hydrocarbons (PAHs), and carbon monoxide (CO) are the primary air pollutants in most urban areas, and many corresponding exposure studies and epidemiologic investigations have been carried out to evaluate their adverse effects (Kok et al, 2005; Kok et al, 2006; Samet, 2007; Garshick et al, 2008; Umbuzeiro et al, 2008). Ambient particles generated by vehicular traffic have received intensive scrutiny, partly because particulates generated from combustion processes pose more serious adverse health effects than those from non-combustion processes and account for more than 50% of the total emissions of PM in the urban areas of highly industrialized countries (Han and Naeher, 2006).
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