Sampling aerosols for lead isotopes on a global scale

To reliably sample aerosols in a wide range of environments from the polluted to the almost pristine, ultra-clean materials, procedures and laboratory conditions are needed. Also, when multiple samples need to be taken at numerous sites the sampling procedures need to be simple and the equipment inexpensive and easy to operate. A system described here which meets these requirements uses a disposable plastic monitor fitted with an acid-cleaned PTFE 0.45 mu m front and a 30-60 mu m backing filter connected to a small diaphragm pump. When ion exchange chemistry is required the system gives a Pb blank 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 giving reliable isotopic data on filters containing >400 pg of Pb. The lowest blank 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/Pb-207 ratios). The factor limiting the quality of measurements below this level is the uncertainty in the blank contribution and not the sensitivity of the thermal ionisation mass spectrometer used here. The analysis of selected 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.