Abstract
Abstract. An intensive aerosol characterization experiment was performed at the Taipei Aerosol and Radiation Observatory (TARO, 25.02° N, 121.53° E) in the urban area of Taipei, Taiwan, during July 2012. Number concentration and size distribution of aerosol particles were measured continuously, which were accompanied by concurrent measurements of mass concentration of submicron particles, PM1 (d ≤ 1 μm), and photolysis rate of ozone, J(O1D). The averaged number concentrations of total (Ntotal), accumulation mode (Nacu), Aitken mode (NAitken), and nucleation mode (Nnuc) particles were 13.9 × 103 cm−3, 1.2 × 103 cm−3, 6.1 × 103 cm−3, and 6.6 × 103 cm−3, respectively. Accordingly, the ultrafine particles (UFPs, d ≤ 100 nm) accounted for 91% of the total number concentration of particles measured in this study (10 ≤ d ≤ 429 nm), indicating the importance of UFPs to the air quality and radiation budget in Taipei and its surrounding areas. An averaged Nnuc / NOx ratio of 192.4 cm−3 ppbv−1 was derived from nighttime measurements, which was suggested to be the characteristic of vehicle emissions that contributed to the "urban background" of nucleation mode particles throughout a day. On the contrary, it was found that the number concentration of nucleation mode particles was independent of NOx and could be elevated up to 10 times of the "urban background" levels during daytime, suggesting a substantial amount of nucleation mode particles produced from photochemical processes. Averages (± 1σ) of the diameter growth rate (GR) and formation rate of nucleation mode particles, J10, were 11.9 ± 10.6 nm h−1 and 6.9 ± 3.0 cm−3 s−1, respectively. Consistency in the time series of the nucleation mode particle concentration and the proxy of H2SO4 production, UVB · SO2/CS, for new particle formation (NPF) events suggested that photooxidation of SO2 was likely one of the major mechanisms for the formation of new particles in our study area. Moreover, it was revealed that the particle growth rate correlated exponentially with the photolysis of ozone, implying that the condensable vapors were produced mostly from photooxidation reactions. In addition, this study also revealed that Nnuc exhibited a quadratic relationship with J10. The quadratic relationship was inferred as a result of aerosol dynamics and featured NPF processes in urban areas.
Highlights
Data Systems and 6.6 × 103 cm−3, respectively
The 95th percentile of Nnuc (31.0 × 103 cm−3) during the new particle formation (NPF) event was twice of that measured on nonevent days. These results suggested that the burst of nucleation mode particles induced by the NPF had caused a significant impact on the particle number concentration during this campaign period
An intensive measurement campaign of particle number concentration, size distribution, and mass concentrations was conducted at an urban aerosol observatory (TARO) in Taipei, Taiwan, during July 2012
Summary
Data Systems and 6.6 × 103 cm−3, respectively. the ultrafine particles (UFPs, d ≤ 100 nm) accounted for 91 % of the to- Atmospheric particulate matter (PM) is one of the main poltal number concentration of particles measured in this study (10 ≤ d ≤ 429 nm), indicating the importance of UFPs to the air quality and radiation budget in Taipei and its surrounding lutants that play an importGanteroolse cinieainr qtuifailcity and climate.PM ing dinirteecrtalcyts(CwhiMathrlossoodnlaeer tlraaDdl.i,ae1ti9vo9ne2;alonMdpyahmlrteeer, s2nt0h0te9c),liamnadteacftosracs-M areas. It was found that the number concentration of nucleation mode particles was indediseases While wthheenaitrheqyuaalrietybrsEetaaanthdreatdrhdins S(hNayvesel,tb2ee0em0n5)s.et up for the mass concentrations of PM10 anSdcPiMe2n.5c(epasrticulate matter pendent of NOx and could be elevated up to 10 times of the “urban background” levels during daytime, suggesting a subwith aerodynamic diameters less than 10 or 2.5 μm, respectively), several studies have indicated the health effects of ulstantial amount of nucleation mode particles produced from trafine particles (UFPs, d ≤ 100 nm) and raised great public photochemical processes. Consistency in the time series of the nucleation number concentrations of urban particulate matter (Stanier et al, 2004; Woo et al, 2001) They can penetrate deeper mode particle concentration and the proxy of H2SO4 production, UVB · SO2/CS, for new particle formation (NPF) events suggested that photooxidation of SO2 was likely one of the major mechanisms for the formation of new particles in our into human lungs than fine and coarse particles (Churg and Brauer, 2000). They can penetrate deeper mode particle concentration and the proxy of H2SO4 production, UVB · SO2/CS, for new particle formation (NPF) events suggested that photooxidation of SO2 was likely one of the major mechanisms for the formation of new particles in our into human lungs than fine and coarse particles (Churg and Brauer, 2000). Oberdorster and Utell (2002) suggested that
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