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

摘要

To better understand the secondary air pollution in transboundary air overwesternmost Japan, ground-based field measurements of the chemicalcomposition of fine particulate matter ( ≤  1 µm), mixing ratios oftrace gas species (CO, O, NO, NO, -pentane, toluene, andethyne), and meteorological elements were conducted with a suite ofinstrumentation. The CO mixing ratio dependence on wind direction showedthat there was no significant influence from primary emission sources nearthe monitoring site, indicating long- and/or mid-range transport of themeasured chemical species. Despite the considerably different atmosphericlifetimes of NO and CO, these mixing ratios were correlated ( = 0.67). The photochemical age of the pollutants, [OH] (the reaction time ×  the mean concentration of OH radical during the atmospherictransport), was calculated from both the NO ∕ NO concentrationratio (NO ∕ NO clock) and the toluene ∕ ethyne concentration ratio(hydrocarbon clock). It was found that the toluene / ethyne concentrationratio was significantly influenced by dilution with background aircontaining 0.16 ppbv of ethyne, causing significant bias in the estimationof [OH]. In contrast, the influence of the reaction of NO withO, a potentially biasing reaction channel on [NO] / [NO],was small. The [OH] values obtained with the NO ∕ NO clock rangedfrom 2.9  ×  10 to 1.3  ×  10 h molecule cmand were compared with the fractional contribution of the ∕ 44 signal to thetotal signal in the organic aerosol mass spectra (, a quantitativeoxidation indicator of carboxylic acids) and O mixing ratio. Thecomparison of [OH] with showed evidence for a systematic increase of as [OH] increased, an indication of secondary organic aerosol (SOA) formation. To a firstapproximation, the increase rate was (1.05 ± 0.03)  ×  10  ×  [OH] h, which is comparable to thebackground-corrected increase rate observed during the New England AirQuality Study in summer 2002. The similarity may imply the production ofsimilar SOA component, possibly humic-like substances. Meanwhile, thecomparison of [OH] with O mixing ratio showed that there was a strongproportional relationship between O mixing ratio and [OH]. A firstapproximation gave the increasing rate and background mixing ratio of ozoneas (3.48 ± 0.06)  ×  10  ×  [OH] ppbv hand 30.7 ppbv, respectively. The information given here can be used forprediction of secondary pollution magnitude in the outflow from the Asiancontinent.