Sampling aerosols for lead isotopes on a global scale

To reliably sample aerosols in a wide range of environments from the pollut ed to the almost pristine, ultra-clean materials, procedures and laboratory conditions are needed. Also, when multiple samples need to be taken at num erous sites the sampling procedures need to be simple and the equipment ine xpensive and easy to operate. A system described here which meets these req uirements uses a disposable plastic monitor fitted with an acid-cleaned PTF E 0.45 mu m front and a 30-60 mu m backing filter connected to a small diap hragm pump. When ion exchange chemistry is required the system gives a Pb b lank of similar to 70 pg. Without ion exchange chemistry the blank amounts to similar to 15 pg on a complete filter sectioned into 8-pi/4 sectors givi ng reliable isotopic data on filters containing >400 pg of Pb. The lowest b lank on the complete filter, without cutting, is 11+/-8 pg which permits Pb isotopes from aerosols to be measured on a similar to 120 pg sized sample with acceptable accuracy and precision (0.2% for Pb-206/Pb-207 and Pb-208/P b-207 ratios). The factor limiting the quality of measurements below this l evel is the uncertainty in the blank contribution and not the sensitivity o f the thermal ionisation mass spectrometer used here. The analysis of selec ted filters from the United Kingdom and the Republic of Ireland are used to illustrate the method. Air containing 0.11 ng m(-3) of Pb yielded isotopic ratios Pb-206/Pb-207=1.083+/-0.003, Pb-208/Pb-207=2.361+/-0.003 and Pb-206 / Pb-204=16.9+/-0.3. (C) 1999 Elsevier Science B.V. All rights reserved.