APPLICATION OF AN IR TRACER TO DETERMINE SOOT EXPOSURE TO STUDENTS COMMUTING TO SCHOOL ON BALTIMORE PUBLIC BUSES

An important component of urban aerosol, diesel soot is a known respir atory irritant and contains mutagenic and carcinogenic organic compoun ds. To estimate Student exposures to soot emitted from public diesel b uses during commutes to city high schools, a portion of the Baltimore municipal fuel supply was tagged with an iridium tracer and exposure w as monitored during commutes with personal aerosol monitors as a part of an Environmental Justice Project. A total of 63.2 g of Ir as iridiu m(III)-2,4-pentanedionate were used to induce a concentration of 48.5 pg Ir l(-1) of fuel. Twenty samples were collected over 10 days while four students commuted on regularly scheduled buses and a fifth studen t commuted by private car. Individual samples integrated from 1 to 4 r ound trips. Iridium analyses were performed instrumentally after neutr on activation with a detection limit (DL) of about 503 fg. For student s commuting by bus and following protocols, Ir tracer concentrations r anged from 53 +/- 38 to > 1980 +/- 49 fg m(-3) Concentrations up to 35 30 +/- 220 fg m(-3) were observed for student # 5, who sampled only wh en boarding and disembarking. Exposure were greatest for students comm uting through the heavily trafficked central business district. Corres ponding estimates of exposures to soot emitted from municipal buses ra nged from less than or equal to 3 to 82 ng soot m(-3) (less than or eq ual to 145 ng m(-3) for student # 5), i.e. well below the exposure lev el of 2-10 mu g m(-3) total C from all sources, including the more tha n 30,000 diesel trucks which,ass through the city's major toll facilit ies each day. Ir was undetectable in samples collected by the student commuting by car when its windows were closed, but comparable to those of the other students when commutes were made with windows open. The Ir tracer DL corresponds to about 21 ng soot, about half of which is c arbon. This is far below the 230 ng reported for analysis by a highly sensitive thermal-optical technique. (C) 1998 Elsevier Science Ltd. Al l rights reserved.