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

Abstract

Fine particulate matters (PM 2.5 ) have been identified as one of the major air pollutants in urban areas, which are responsible for the deterioration of the atmospheric air quality as well as adverse effects on public health. In this study, the mass concentration, water-soluble ionic component, trace metal component, carbon component and modeling the contribution source for PM 2.5 was characterized for Chiayi City, which has high population density and surrounded by agricultural area. The lowest PM 2.5 mass concentrations were registered in the summer (9-22 µg m -3 ), while for the spring, autumn, and winter were well above the healthy level suggested by World Health Organization (WHO). For all seasons, the dominants were the sulfate (SO 4 2-), nitrate (NO 3 -) and followed closely by ammonium (NH 4 + ). Those secondary aerosols were transformed from SO 2 and NO 2 into particulate NO 3 -and SO 4 2-during spring, autumn and winter. Lower carbon mass concentrations were observed for summer (2.03-2.49 µg m -3 ) corresponding to the highest carbon content in PM 2.5 mass concentrations in terms of percentages (average 18.1%). Using the Chemical Mass Balance receptor model, the secondary nitrate (NO 3 -), primary traffic source, secondary sulfate (SO 4 2-), re-suspending soil particle, and petrochemical industry were identified as the major sources of PM 2.5 in Chiayi City. Consequently, the PM 2.5 contributions were complicated in a small but various seasons and geological distributing area. The air quality control strategies were thus seasonal and periodical dependent.

Reduction of Atmospheric PM2.5 Level by Restricting the Idling Operation of Buses in a Busy Station

“…However, the NO 3 -content in total ions increased about 3.1% (15.5 → 18.6%) from upwind to exposure site, while SO 4 2-and NH 4 + kept in the similar fractions (53.5 and 22.1%, respectively) to the upwind site. The trend of high concentration of nitrite ion (NO 3 -) within fine particulate matter PM 2.5 was similar with previous studies that claimed the heavy traffic especially diesel vehicles tend to emit NOx and further oxidized to form NO 3 -in the air (Chang et al, 2013;Peters et al, 2013;Tseng et al, 2016). Moreover, the semi-close geometry of the potential emission area inside the bus station could provide a canyon effect to accumulate the NO x , NH 4 + , and other pollutants for a longer time to form the NO 3 -contents (Jin et al, 2017).…”

“…The sulfur oxidation ratio (SOR) and nitrogen oxidation ratio (NOR) are two important value in neutralizing processes towards particulate matter to ambient air (Tseng et al, 2016 Before restriction, SOR were 0.469 and 0.451 at the upwind and exposure sites, respectively, on weekend, while NOR were 0.089 and 0.084, respectively (as shown in Table 1). Additionally, SOR value were 0.537 and 0.493 at the upwind and exposure sites, respectively, on weekday, then NOR value were 0.088 and 0.090, respectively.…”

“…They were calculated by the following equations in the current study. + is sufficient to neutralize both NO 3 -and SO 4 2-to form sulfate and nitrate as fine particles (Tseng et al, 2016). Fig.…”

“…There were other studies claimed the major ions emitted are K + and Cl -during crop burning, and K + from forest fires (Sillapapiromsuk et al, 2013). Generally, sulfate (SO 4 2-) and nitrate (NO 3 -) have higher fractionations than others which identified as anthropogenic emission, when ammonium (NH 4 + ) could be emitted from the potential sources of fermentation products of agricultural waste and plant decomposition, livestock operation, biomass burning, and natural soils around southern Taiwan (Chen et al, 2015;Tseng et al, 2016). The anion/cation equivalent ratios were all around 1.0 as shown in Fig.…”

“…(Steinfeld, 1998). The amount of NH 4 + determine how much contradictive ions could be neutralize (Tseng et al, 2016). I and J values are the indexes to quantify how far the neutralization processing is ideally allowed.…”