Abstract
ABSTRACTChemical characteristics of aerosols (PM1 (on-line measurement) and PM2.5 (off-line measurement) were investigated in coastal and urban atmospheres. Organics were the most dominant species in PM1 at both sites, exhibiting little difference in the relative fractions of chemical constituents in PM1 (organics, sulfate, black carbon (BC), nitrate, ammonium and chloride) between two sites. However, a clear difference in the types of organics was found between the two sites. The fraction of oxidized (aged) organics was much higher at coastal site than at urban site. The nitrate fraction significantly increased at both sites in PM2.5 compared with that in PM1, suggesting that a significant amount of nitrate exists at particle sizes of 1 µm–2.5 µm. Additionally, the aerosols observed at coastal site were acidic. At both sites, photochemical activity played an important role in enhancing sulfate and oxidized organics in the afternoon, thereby overcoming the dilution effect. More distinct diurnal patterns were observed for nitrate, BC and organics at the urban site compared to the coastal site. Chemical characteristics also varied with different air masses. The highest PM concentration was associated with the northwest continental air mass (the air mass passed over heavy industrial areas before arriving at the site and moved slowly compared to other air masses). Three PM events (sulfate-dominant versus organic-dominant) were observed during the sampling periods and were considered long-range transport (LTP) events. The water-soluble organic carbon (WSOC) and oxidized organic contents significantly increased during LTP events, suggesting that organics were highly aged during transport.
Highlights
Fine (< 2.5 μm) and ultrafine (< 100 nm) particles in the ambient atmosphere are of interest due to their effects on the Earth’s radiation balance via scattering or absorbing solar light (Solomon et al, 2007), visibility impairment (Chow et al, 2002; Chang et al, 2009), cloud formation by acting as cloud condensation nuclei (CCN) (Solomon et al, 2007) and atmospheric chemistry (Reid and Sayer, 2002)
Temperature and local wind speed were lower at the urban site than the coastal site during the given sampling period
Fractions of chemical constituent (organics, sulfate, black carbon (BC), nitrate, ammonium and chloride) in PM1 were similar at both sites, the PM mass concentration was much lower at the coastal site than at the urban site
Summary
Fine (< 2.5 μm) and ultrafine (< 100 nm) particles in the ambient atmosphere are of interest due to their effects on the Earth’s radiation balance via scattering or absorbing solar light (Solomon et al, 2007), visibility impairment (Chow et al, 2002; Chang et al, 2009), cloud formation by acting as cloud condensation nuclei (CCN) (Solomon et al, 2007) and atmospheric chemistry (Reid and Sayer, 2002) These particles influence human health (Dockery and Pope, 1994; Peters et al, 1997). They are directly emitted from various emission sources, such as industries, biomasses, vehicles and deserts (primary aerosols), or formed by gas-toparticle conversion processes (secondary aerosols) (Andreae, 2007).
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