Detection of Atmospheric Particulate Metals in Near Real-Time: Tunnel, Urban and Rural Environments

We have developed an instrument for monitoring particulate metals in the atmosphere in near real time, called Toxic-metal Aerosol Real Time Analyzer (TARTA). TARTA uses spark-induced breakdown spectroscopy (SIBS), which is akin to Atomic Emission Spectroscopy. TARTA is inexpensive, responds to multiple elements, has high temporal resolution and high sensitivity, is compact, and uses little power. In this study, TARTA is evaluated on its ability to measure PM_2.5 metals in three environments: traffic-related emissions in the Caldecott tunnel, urban emissions near downtown Sacramento, and agricultural emissions from a rural background site in Davis, CA, USA. We identified multiple elements, such as trace metals associated with vehicle engines, automotive brakes, and tire wear (Cr, Zn, Cu, and Fe), as well as crustal metals from the resuspended dust (Na, Mg, and Al). At the Caldecott tunnel, elemental concentrations averaged 24 ± 15 ng m^–3 for Cu, 295 ± 160 ng m^–3 for Fe, 102 ± 44 ng m^–3 for Mg, 13 ± 13 ng m^–3 for Zn, and 16 ± 7 ng m^–3 for Cr. In contrast, the rural site showed lower concentrations of Cu (15 ± 6 ng m^–3), Fe (26 ± 13 ng m^–3), and Cr (11 ± 4 ng m^–3) but higher for Mg (132 ± 40 ng m^–3). The urban site in Sacramento recorded intermediate values with Fe concentrations at 60 ± 56 ng m^–3 and Cr at 13 ± 9 ng m^–3. TARTA showed varying degrees of agreement with established techniques (online and offline X-ray fluorescence (XRF) analysis) for different metals, with the best correlations for Zn (Pearson’s correlation coefficient, R = 0.35 to 0.61 during specific periods) and the worst correlation for Fe (R = 0.09).