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Volume 16, issue 7 | Copyright
Atmos. Chem. Phys., 16, 4555-4568, 2016
© Author(s) 2016. This work is distributed under
the Creative Commons Attribution 3.0 License.

Research article 13 Apr 2016

Research article | 13 Apr 2016

Photochemical age of air pollutants, ozone, and secondary organic aerosol in transboundary air observed on Fukue Island, Nagasaki, Japan

Satoshi Irei1,a, Akinori Takami1, Yasuhiro Sadanaga2, Susumu Nozoe1,b, Seiichiro Yonemura3, Hiroshi Bandow2, and Yoko Yokouchi1 Satoshi Irei et al.
  • 1National Institute for Environmental Studies, 16-2 Onogawa, Tsukuba, Ibaraki 305-8506, Japan
  • 2Department of Applied Chemistry, Graduate School of Engineering, Osaka Prefecture University, 1-1 Gakuencho, Naka-ku, Sakai, Osaka 599-8531, Japan
  • 3National Institute for Agro-Environmental Sciences, 3-1-3 Kannondai, Tsukuba, Irabaki 305-8604, Japan
  • apresent address: Department of Biology, Chemistry, and Marine Science, University of the Ryukyus, 1 Senbaru, Nishihara, Okinawa 903-0213, Japan
  • bpresent address: National Museum of Emerging Science and Innovation, Aomi 2-3-6, Koto, Tokyo 135-0064, Japan

Abstract. To better understand the secondary air pollution in transboundary air over westernmost Japan, ground-based field measurements of the chemical composition of fine particulate matter ( ≤ 1µm), mixing ratios of trace gas species (CO, O3, NOx, NOy, i-pentane, toluene, and ethyne), and meteorological elements were conducted with a suite of instrumentation. The CO mixing ratio dependence on wind direction showed that there was no significant influence from primary emission sources near the monitoring site, indicating long- and/or mid-range transport of the measured chemical species. Despite the considerably different atmospheric lifetimes of NOy and CO, these mixing ratios were correlated (r2 = 0.67). The photochemical age of the pollutants, t[OH] (the reaction time  ×  the mean concentration of OH radical during the atmospheric transport), was calculated from both the NOxNOy concentration ratio (NOxNOy clock) and the tolueneethyne concentration ratio (hydrocarbon clock). It was found that the toluene/ethyne concentration ratio was significantly influenced by dilution with background air containing 0.16ppbv of ethyne, causing significant bias in the estimation of t[OH]. In contrast, the influence of the reaction of NOx with O3, a potentially biasing reaction channel on [NOx]/[NOy], was small. The t[OH] values obtained with the NOxNOy clock ranged from 2.9 × 105 to 1.3 × 108hmoleculecm−3 and were compared with the fractional contribution of the mz 44 signal to the total signal in the organic aerosol mass spectra (f44, a quantitative oxidation indicator of carboxylic acids) and O3 mixing ratio. The comparison of t[OH] with f44 showed evidence for a systematic increase of f44 as t[OH] increased, an indication of secondary organic aerosol (SOA) formation. To a first approximation, the f44 increase rate was (1.05±0.03) × 10−9 × [OH]h−1, which is comparable to the background-corrected increase rate observed during the New England Air Quality Study in summer 2002. The similarity may imply the production of similar SOA component, possibly humic-like substances. Meanwhile, the comparison of t[OH] with O3 mixing ratio showed that there was a strong proportional relationship between O3 mixing ratio and t[OH]. A first approximation gave the increasing rate and background mixing ratio of ozone as (3.48±0.06) × 10−7 × [OH]ppbv h−1 and 30.7ppbv, respectively. The information given here can be used for prediction of secondary pollution magnitude in the outflow from the Asian continent.

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Short summary
Field measurements for trace-level chemical species in the gas and particulate phases were conducted at a rural site in westernmost Japan to better understand formation of secondary pollutants in transboundary air. A comparison of photochemical ages estimated by chemical clock with ozone concentrations or fractions of carboxylate in organic aerosol showed proportional relationships, and their slopes were 3.48 × 10−7 ppbv molecule−1 cm3 h−1 and 1.05 × 10−9 molecule−1 cm3 h−1, respectively.
Field measurements for trace-level chemical species in the gas and particulate phases were...