GEOCHEMISTRY OF ATMOSPHERIC AEROSOLS ON CAPE COD, MA: IMPLICATIONS FOR AIR QUALITY AND HUMAN HEALTH

In order to understand source influences on ambient aerosol chemistry, and to determine possible links between aerosol composition, mass variation, and possible health impacts, a detailed time series of aerosol samples was collected from late winter to mid summer, 2008, on the Quissett Campus of Woods Hole Oceanographic Institute, at the southwestern tip of Cape Cod, MA. The study area is largely rural to residential, but is located within 100 km of the urban centers of Boston, MA, and Providence, RI. Air-mass trajectories and high levels of ozone and other pollutants, especially during the summer months, suggest that air quality on Cape Cod is influenced by northeastern urban centers, and this may contribute to unusually high asthma rates.

Sampling encompassed detailed (12-hour) collection of fine particulate (PM_2.5) and total suspended particulate (TSP) samples (having no particle-size limitation), over approximately one-week periods in February and July/August, 2008. In addition, near continuous fine particulate sampling in1- to 6-day intervals was conducted from early April to early August, 2008. Particulate sampling was done together with deployment of the USGS mobile mercury laboratory, which provided near real-time results for PM_2.5 mass concentrations, atmospheric mercury species, and concentrations of ozone and other gaseous pollutants.

Particulate samples were extracted from filter media and analyzed by ICP-MS for a suite of 38 elements, at USGS laboratories. For 12-hour PM_2.5 samples collected at a rate of 42 liters per minute, concentrations of Al, Cd, Mg, Na, Sr, and V exceed detection limits in nearly all cases, whereas As, Ba, Ce, Ga, La, Rb, Sb, Y, and Zn, are quantifiable in approximately half of the samples. A greater number of elements are measureable in the TSP samples and in PM_2.5 samples collected over 24 hours or more. The long term fine particulate sampling shows sample-to-sample variation within about a factor of 5-10 of baseline values for a wide range of elements, with the exception of some greater enrichments (20 to100 times baseline for Ba, Bi, Cu, Pb, Sb, Sr, Ti, and Zn), in samples collected over the July 4 holiday. Initial results for source attribution indicate that trace elements in PM_2.5 are derived from crustal, anthropogenic, sea salt, oil combustion, and one other unidentified source.