| Abstract
| - Haloacetic acid (HAA) concentrations were measured inair samples from a semi-rural and a highly urbanized site insouthern Ontario throughout 2000 to investigate theirsources and gas−particle partitioning behavior. Denuderswere efficient for collection of gaseous HAAs, and theparticle phase was collected on a downstream quartz filterwith negligible breakthrough. Total HAA concentrations(i.e., gas + particles) ranged between <0.025 and 19 ng m-3for individual HAAs at both sites. The dominant airborneHAA was monochloroacetic acid (MCA), followed indecreasing order by dichloroacetic acid (DCA), trifluoroaceticacid (TFA), and trichloroacetic acid (TCA). Difluoroaceticacid (DFA), monofluoroacetic acid (MFA), and chlorodifluoroacetic acid (CDFA) were also frequently detected atlower concentrations. Between sites, TFA, DFA, MFA,and TCA concentrations were significantly higher in Toronto,while CDFA concentrations were higher in Guelph. HAAswere primarily in the gas phase all year; however, duringcolder months, particle-phase HAA concentrationsincreased relative to the gas phase. Trichloroacetic acidhad the highest particle fraction (φ) for all detected HAAs,with a mean φ of 0.51 and 0.56 for Guelph and Toronto,respectively, and both vapor pressure and acid strengthappeared to influence gas−particle partitioning. Temporaltrends at both sites were partially explained by temperature,short-wave radiation, and particle mass (PM10), leading toindications of the respective sources. A simple depositionmodel indicated that dry deposition of TFA and TCAshould not be neglected in temperate mid-latitudeenvironments and that precipitation concentrations canbe successfully predicted by the Henry's law constant.
|
