Trends in PM_2.5 transition metals in urban areas across the United States

Abstract

Using data from the Environmental Protection Agency's Chemical Speciation Network, we have characterized trends in PM 2.5 transition metals in urban areas across the United States for the period 2001-2016. The metals included in this analysis-Cr, Cu, Fe, Mn, Ni, V, and Zn-were selected based upon their abundance in PM 2.5 , known sources, and links to toxicity. Ten cities were included to provide broad geographic coverage, diverse source influences, and climatology: Atlanta (ATL), Baltimore (BAL), Chicago (CHI), Dallas (DAL), Denver (DEN), Los Angeles (LA), New York City (NYC), Phoenix (PHX), Seattle (SEA), and St. Louis (STL). The concentrations of V and Zn decreased in all ten cities, though the V decreases were more substantial. Cr concentrations increased in cities in the East and Midwest, with a pronounced spike in concentrations in 2013. The National Emissions Inventory was used to link sources with the observed trends; however, the causes of the broad Cr concentration increases and 2013 spike are not clear. Analysis of PM 2.5 metal concentrations in port versus non-port cities showed different trends for Ni, suggesting an important but decreasing influence of marine emissions. The concentrations of most PM 2.5 metals decreased in LA, STL, BAL, and SEA while concentrations of four of the seven metals (Cr, Fe, Mn, Ni) increased in DAL over the same time. Comparisons of the individual metals to overall trends in PM 2.5 suggest decoupled sources and processes affecting each. These metals may have an enhanced toxicity compared to other chemical species present in PM, so the results have implications for strategies to measure exposures to PM and the resulting human health effects.

The Effect of Transportation and Wildfires on the Spatiotemporal Heterogeneity of PM2.5 Mass in the New York-New Jersey Metropolitan Statistical Area

“… 19 , 30 The ambient levels of tracers of industrial emissions (Cr, Cu, Fe, and Mn) and crude oil (Ni, V) combustion also declined during the same period. 19 , 31 Slightly higher declining rates were computed for heavily populated urban sites in NYC and NJ as compared to those computed for peri-urban sites. A less pronounced decline has been also observed in the Upstate New York region farther away from the major urban centers with reduction rates of 3 to 4 µg/m 3 /year.…”

“…It has been previously shown that wildfires smoke concentrations were strongly related the frequency and magnitude of wildfires in eastern US. 13 - 36 In this analysis, industrial and residential wood combustion were included in the industrial sector emissions. According to the 2014 NEI, 14 000 metric tons of PM 2.5 (one-third of industrial emissions) were emitted from biomass burning accounting for approximately 93% of residential wood combustion.…”

Precipitation of aqueous transition metals in particulate matter during the dithiothreitol (DTT) oxidative potential assay

“…For the precipitation experiments, SRM-1648a extract was added to the DTT assay at three concentration levels (Table 1), which were selected according to the range of Fe concentrations measured in ten urban areas across the US using accepted PM lter sampling and extraction protocols. 36,49,50 The concentrations of the remaining elements were calculated based on the dilution factor (DF) and the elements' concentration in the SRM-1648a extract. Note that the Cu concentration for samples 1, 2, and 3 and Mn concentration for samples 1 and 2 were below the DL for the colorimetric analysis.…”

“…Note that the Cu concentration for samples 1, 2, and 3 and Mn concentration for samples 1 and 2 were below the DL for the colorimetric analysis. To maintain the relevance of Mn and Cu concentrations to that in PM lter extracts (0.058 mM Mn and 0.06 mM Cu), 36,49,50 increasing the SRM-1648a sample concentrations above the DL for Mn and Cu was not preferred. Also presented in Table 1 are metal solubilities and saturation indexes (SI) determined by MINEQL 36,81 under the DTT assay conditions (0.1 M TOTPO 4 , T ¼ 37 C, pH ¼ 7.4 and ionic strength ¼ 0.22 M).…”

“…Precipitation when aqueous metals from PM extracts and metal-salts are added to the DTT assay is detected using a combination of approaches. Our analysis is focused on Fe (Fe(II) and Fe(III)) because of its high concentration in PM, 49,50 and Cu(II) and Mn(II) due to their high reactivity in the DTT assay. 13,51,52 Precipitate formation and metal removal in the chemically complex PM extracts are compared to experiments conducted with metal salts to elucidate interactions and effects of multiple species in the DTT assay matrix.…”