title: Seasonal and long-term trends in atmospheric PAH concentrations: evidence and implications.
abstract: Atmospheric monitoring data for selected polynuclear aromatic hydrocarbons (PAHs) were compiled from remote, rural and urban locations in the UK, Sweden, Finland and Arctic Canada. The objective was to examine the seasonal and temporal trends, to shed light on the factors which exert a dominant influence over ambient PAH levels. Urban centres in the UK have concentrations 1-2 orders of magnitude higher than in rural Europe and up to 3 orders of magnitude higher than Arctic Canada. Interpretation of the data suggests that proximity to primary sources 'drives' PAH air concentrations. Seasonality, with winter (W) > summer (S), was apparent for most compounds at most sites; high molecular weight compounds (e.g. benzo[a]pyrene) showed this most clearly and consistently. Some low molecular weight compounds (e.g. phenanthrene) sometimes displayed S>W seasonality at some rural locations. Strong W>S seasonality is linked to seasonally-dependent sources which are greater in winter. This implicates inefficient combustion processes, notably the diffusive domestic burning of wood and coal. However, sometimes seasonality can also be strongly influenced by broad changes in meteorology and air mass origin (e.g. in the Canadian Arctic). The datasets examined here suggest a downward trend for many PAHs at some sites, but this is not apparent for all sites and compounds. The inherent noise in ambient air monitoring data makes it difficult to derive unambiguous evidence of underlying declines, to confirm the effectiveness of international source reduction measures.
authors.affiliation: Environmental Science Department, Institute of Environmental and Natural Sciences, Lancaster University, LA1 4YQ, Lancaster, UK.
authors.forename: Konstantinos
authors.initials: K
authors.lastname: Prevedouros
authors.forename: Eva
authors.initials: E
authors.lastname: Brorström-Lundén
authors.forename: Crispin
authors.initials: C
authors.lastname: J  Halsall
authors.forename: Kevin C
authors.initials: KC
authors.lastname: Jones
authors.forename: Robert G M
authors.initials: RG
authors.lastname: Lee
authors.forename: Andrew J
authors.initials: AJ
authors.lastname: Sweetman
mesh_terms: D000383:Agriculture; D000393:Air Pollutants / Q000032:analysis*; D000397:Air Pollution / Q000032:analysis / Q000706:statistics & numerical data*; D003625:Data Collection; D004784:Environmental Monitoring / Q000379:methods*; D006207:Half-Life; D007221:Industry; D011084:Polycyclic Aromatic Hydrocarbons / Q000032:analysis*; D012621:Seasons; D013997:Time Factors
chemical_list: D000393:Air Pollutants; D011084:Polycyclic Aromatic Hydrocarbons