Seasonal, anthropogenic. air mass, and meteorological influences on the atmospheric concentrations of polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDD/Fs): Evidence for the importance of diffuse combustion sources

Sampling programs were undertaken to establish air polychlorinated dibenzo- p-dioxins and dibenzofurans (PCDD/F) concentrations at a semirural site on the northwest coast of England in autumn and summer and to investigate fact ors causing their variability. Changing source inputs, meteorological param eters, air masses, and the impact of a festival when it is customary to lig ht fireworks and bonfires were investigated. Various lines of evidence from the study point to diffuse, combustion-related sources being a major influ ence on ambient air concentrations. Higher PCDD/F concentrations were gener ally associated with air masses that had originated and moved over land, pa rticularly during periods of low ambient temperature. Low concentrations we re associated with air masses that had arrived from the Atlantic Ocean/Iris h Sea to the west of the sampling site and had little or no contact with ur ban/industrialized areas. Concentrations in the autumn months (similar to 1 to 20 pg m(-3) of Sigma(4-8)CDD/Fs) were 2 to 10 times higher than those f ound in the summer (similar to 0.4 to 0.7 pg m-3 of Sigma(4-8)CDD/Fs). Conc entrations in the autumn rose as ambient temperatures decreased; the eviden ce that diffuse domestic heating (combustion) sources are responsible for t his increase is discussed. A sample with concentrations 2 to 3 times above ambient levels was associated with a specific air mass originating from the Mediterranean that moved over Spain and France toward the United Kingdom ( UK). Concentrations also increased substantially, by a factor of >10, durin g the autumnal festival. It is estimated that similar to 30 g of sum of tox ic equivalents (Sigma TEQ) of PCDD/Fs may have been emitted into the UK atm osphere during a 3-day period at this time. This amount is similar to 5-14% of the estimated contemporary annual national primary emissions of PCDD/Fs in the UK and implicates uncontrolled burning of wood, garden refuse, and wastes an the bonfires and/or the lighting of fireworks as diffuse sources of PCDD/Fs.