Long-term PAN measurements from eastern Scotland (1993-1999)

Abstract Hourly measurement data for PAN (peroxyacetyl nitrate) mixing ratios in the atmosphere at a rural site at Bush Estate, Penicuik EH26 0QB (CEH Edinburgh), 15 km south of Edinburgh, from 1993 to 1999 in ppt (parts in 10^12). Measurements were made using a gas chromatograph with electron capture detector. Annual average concentrations were between 0.1 and 0.15 nl l-1, with episodes up to 3 nl l-1 in long-range transported polluted air. PAN concentrations were approximately log-normally distributed. The concentrations measured are the result of a balance between photochemical production rates and removal by thermal decomposition and dry deposition. There was a pronounced seasonal maximum in PAN concentrations in late spring, and a strong diurnal cycle only in April-June, with a maximum at 1700 h. Individual episodes, with concentrations up to 3 nl l-1, could be traced over distances of ca. 1000 km, with rapid changes in concentration as the prevailing winds advected polluted air masses across the site.