The low level detection of air pollutants requires reliable sampling and calibration techniques, as well as using sophisticated analytical instrumentation. Incorporating these requirements into a mobile platform allows for accurate, curb side measurement of airborne ambient chemicals in real time. In this case study, air emissions from two manufacturing facilities in close proximity to each other were monitored with a mobile unit to chemically characterize and differentiate the emissions from each facility. Based upon the downwind fingerprinting and concentration levels, the mobile unit was able to isolate the source of the emissions to the responsible facility. A few chemicals which were detected by the TAGA had never been reported by the companies. Real time proximity monitoring was accomplished by using a triple quadrupole mass spectrometer (TAGA Ile). The TAGA He interfaces with a low pressure chemical ionization source that operates at 3 Torr and 100 LA. By monitoring the response of specific parent/daughter ion pairs, the TAGA Ile unit was able to determine the point-of-impingement concentrations of styrene and other ambient airborne chemicals. Positive identification and quantitation of styrene was accomplished by multiple measurements of the following ion pairs: 104/78, 104/77, 104/65 and 104/52. By optimizing various parameters of the TAGA Ile a method detection limit of 1.1 mu g/m(3) was achieved for styrene. A daily multi-point calibration was performed using a liquid standard. The maximum half-hour average concentration of styrene measured downwind of the two facilities was 2300 mu g/m(3) and the maximum instantaneous level was measured at 15,000 mu g/m(3). The mobile capability of the unit was also utilized in determining the ambient airborne concentration of styrene at various distances from the companies with the maximum levels measured at close proximity to the emission sources. (c) 2005 Elsevier B.V. All rights reserved.