Ambient measurements of metal-containing PM2.5 in an urban environment using laser-induced breakdown spectroscopy

Laser-induced breakdown spectroscopy (LIBS) was used to measure the distribution of seven species in individual ambient aerosol particles during an 8-day period from 26 August to 2 September 2002 at the Pittsburgh Aerosol Supersite. Particle hit rates were on the order of 10−4–10−5 for Al, Ca, Cr, Cu, Mg, Mn, and Na. Weekly average concentrations between 29 and 720 ng m−3 are reported along with conservative threshold detection limits for individual particles between 15 and 184 fg, depending on the element. Hourly concentrations are reported for Ca, Mg, and Na; Mg concentrations are found to be somewhat correlated with both Ca and Na, while Ca and Na appear uncorrelated. A representative example of measured Mg particle masses illustrates that the detection threshold poses a limitation in this data set, which could be rectified in future implementations. Finally, the presence of multi-element particles in the data set suggest the use of high-sensitivity, wide-range echelle spectrometers for particle source apportionment and determination of associations between elements.