Satoshi Irei , Akinori Takami, Yasuhiro Sadanaga, Susumu Nozoe, Seiichiro Yonemura, Hiroshi Bandow, and Yoko Yokouchi

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 ( ≤ 1 μm), mixing ratios of trace gas species (CO, O₃, NO_x, NO_y, 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 NO_y and CO, these mixing ratios were correlated (r² = 0.67). The photochemical age of the pollutants, t[OH] (the reaction time ×ばつ the mean concentration of OH radical during the atmospheric transport), was calculated from both the NO_x ∕ NO_y concentration ratio (NO_x ∕ NO_y clock) and the toluene ∕ ethyne concentration ratio (hydrocarbon clock). It was found that the toluene / ethyne concentration ratio was significantly influenced by dilution with background air containing 0.16 ppbv of ethyne, causing significant bias in the estimation of t[OH]. In contrast, the influence of the reaction of NO_x with O₃, a potentially biasing reaction channel on [NO_x] / [NO_y], was small. The t[OH] values obtained with the NO_x ∕ NO_y clock ranged from 2.9 ×ばつ 10⁵ to 1.3 ×ばつ 10⁸ h molecule cm⁻³ and were compared with the fractional contribution of the m∕z 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) ×ばつ 10⁻⁹ ×ばつ [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) ×ばつ 10⁻⁷ ×ばつ [OH] ppbv h⁻¹ and 30.7 ppbv, respectively. The information given here can be used for prediction of secondary pollution magnitude in the outflow from the Asian continent.

How to cite. Irei, S., Takami, A., Sadanaga, Y., Nozoe, S., Yonemura, S., Bandow, H., and Yokouchi, Y.: Photochemical age of air pollutants, ozone, and secondary organic aerosol in transboundary air observed on Fukue Island, Nagasaki, Japan, Atmos. Chem. Phys., 16, 4555–4568, https://doi.org/10.5194/acp-16-4555-2016, 2016.

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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 ×ばつ 10⁻⁷ ppbv molecule⁻¹ cm³ h⁻¹ and 1.05 ×ばつ 10⁻⁹ molecule⁻¹ cm³ h⁻¹, respectively.

Field measurements for trace-level chemical species in the gas and particulate phases were...

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