Size Spectra and Atmospheric Growth of V-Containing Aerosol in Washington, DC

Size-segregated submicrometer aerosol particles were collected with micro-orifice impactors (MOI) at three sites in the heavily urban, but nonindustrial-ized Washington, DC metropolitan area during a 40-day period in August and September of 1990, when atmospheric V (an important marker of oil combustion emissions) was principally derived from commercial and utility oil combustion. Results for 34 MOI samples, analyzed for V by instrumental neutron activation analysis, were fit with a least-squares technique which used impactor calibration data to determine log-normal distribution parameters, i.e., mass median aerodynamic diameter (mmad) and geometric standard deviation σg; for fine particles bearing V. Geometric size distribution parameters were also determined. The median mmad for 19 College Park (CP) samples was 0.361 ± 0.006 μm. At this site, mmads for samples collected in the absence of rain and with V concentrations > 0.61 ng/m3 increased continuously with increasing relative humidity (RH) from 56% to 79% according to the equation dp3= -0.0222 ± 0.0033/ln(aw) - 0.013 ± 0.009. Mmads for samples collected at Andrews AFB were characteristically smaller than those determined at CP at comparable RH, probably due to the influence of a nearby oil-fired boiler.