Two decades of atmospheric measurements of polycyclic aromatic hydrocarbons (PAHs) were conducted at three Arctic sites, i.e., Alert, Canada; Zeppelin, Svalbard; and Pallas, Finland. PAH concentrations decrease with increasing latitude in the order of Pallas > Zeppelin > Alert. Forest fire was identified as an important contributing source. Three representative PAHs, phenanthrene (PHE), pyrene (PYR), and benzo­[a]­pyrene (BaP) were selected for the assessment of their long-term trends. Significant decline of these PAHs was not observed contradicting the expected decline due to PAH emission reductions. A global 3-D transport model was employed to simulate the concentrations of these three PAHs at the three sites. The model predicted that warming in the Arctic would cause the air concentrations of PHE and PYR to increase in the Arctic atmosphere, while that of BaP, which tends to be particle-bound, is less affected by temperature. The expected decline due to the reduction of global PAH emissions is offset by the increment of volatilization caused by warming. This work shows that this phenomenon may affect the environmental occurrence of other anthropogenic substances, such as more volatile flame retardants and pesticides.

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Abstract. Aerosol and trace gas measurements were made at Kejimkujik National Park, Nova Scotia, Canada, during the summer of 1996. A case study from July 7-8 provides evidence of nucleation and condensation of products related to the oxidation of different biogenic emissions. Particles from 5 nm to 50 nm in diameter evolved during the afternoon and early evening associated with variations in isoprene. Late in the evening the ix-and [5-pinene mixing ratios and the aerosol particle volume increased. Soon after, there was a sharp increase in RO2H/H202 that persisted until about 0100 LT. The initial increases in the pinenes and aerosols were strong and influenced by changes in winds. After 2200 LT, and into the early morning, the winds were relatively steady, and the ix- supersaturation were enhanced by the appearance of the 80-90 nm mode pointing to at least some of these forest-generated particles as being able to serve as nuclei for cloud droplets at common atmospheric supersaturations.

The concentrations of perfluoroalkyl acids (PFAAs) were determined in precipitation from three locations across the Great Lakes between 2006 and 2018 and compared to those in surface water. Perfluorooctane sulfonate (PFOS) and perfluorooctanoate (PFOA) concentrations generally decreased in precipitation, likely in response to phase-outs/regulatory actions. In comparison, concentrations of shorter-chained PFAA, which are not regulated in Canada did not decrease and those of perfluorohexanoate and perfluorobutanoate (PFBA) recently increased, which could be due to their use as replacements, as the longer-chained PFAAs are being phased-out by industry. PFOS and PFOA concentrations were greater in Lake Ontario precipitation than in precipitation from more remote locations. In comparison, PFBA concentrations were comparable across locations, suggesting greater atmospheric transport either through its more volatile precursors and/or directly in association with particles/aerosols. In Lake Ontario, the comparison of PFAAs in precipitation to those in surface water provides evidence of sources (e.g., street dust and wastewater effluent) in addition to wet deposition to surface water, whereas wet deposition appears to be dominant in Lakes Huron and Superior. Our results suggest that source control of shorter-chained PFAAs may be slow to be reflected in environmental concentrations due to emissions far from the location of detection and continued volatilization from existing in-use products and waste streams.

>0.065/•m) ranged from 10 to 922 cm-with an average of 270 cm-. Mixing ratios of particulate Br-compounds were observed to be anticorrelated with that of ozone, increasing markedly when the ozone mixing ratio was <10 nmol/mol. There was no obvious dependence of the ratio of gas to particle Br-on ozone mixing ratio. Observations suggested that during ozone depletion events the number concentration of particles increased in the 1.0 to 1.4/•m ESD diameter range (ambient relative humidity). IntroductionThe observations reported here were collected as part of the second field campaign of the Arctic Tropospheric Ozone Chemistry study in spring 1996 (ARCTOC'96). The study was undertaken to shed more light on the processes involved in the episodic depletion of tropospheric ozone in the Arctic spring. Denuder measurements have proven to be valuable in determining the partitioning of semi-volatile compounds of bromine and nitrogen between particulate and gaseous phases [Bartie et al., 1994a;Li, 1994]. This information is essential in diagnosing heterogeneous reactions involved in the ozone depletion process, such as those that recycle reactive halogens and nitrogen compounds. In this study, measurements were undertaken to characterize physical and chemical aerosol properties relevant to their role in ozone depletion chemistry at Ny •lesund. This paper presents and discusses the results. 5515