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 nonindustrialized 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 (sigma(g)) 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 mu m At this site, mmads for samples collected in the absence of rain and with V concentrations > 0.61 ng/m(3) increased continuously with increasing relative humidity (RH) from 56% to 79% according to the equation d(p)(3) = -0.0222 +/- 0,0033/ln(a(w)) - 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.