Barbara J. Turpin

Secondary organic aerosol yields from cloud‐processing of isoprene oxidation products

[1]xa0While there is a growing understanding from laboratory studies of aqueous phase chemical processes that lead to secondary organic aerosol (SOA) formation in cloud droplets (SOAdrop), the contribution of aqueous phase chemistry to atmospheric SOA burden is yet unknown. Using a parcel model including a multiphase chemical mechanism, we show that SOAdrop carbon yields (Yc) from isoprene (1) depend strongly on the initial volatile organic carbon (VOC)/NOx ratio resulting in 42% > Yc > 0.4% over the atmospherically-relevant range of 0.25 < VOC/NOx < 100; (2) increase with increasing cloud-contact time; (3) are less affected by cloud liquid water content, pH, and droplet number. (4) The uncertainty associated with gas/particle-partitioning of semivolatile organics introduces a relative error of −50% ≤ ΔYc < +100 %. The reported yields can be applied to air quality and climate models as is done with SOA formed on/in concentrated aerosol particles (SOAaer).

Contribution of organosulfur compounds to organic aerosol mass.

Organosulfates have been proposed as products of secondary organic aerosol formation. While organosulfates have been identified in ambient aerosol samples, a question remains as to the magnitude of their contribution to particulate organic mass. At the same time, discrepancies have been observed between total particulate sulfur measured by X-ray fluorescence (XRF) spectroscopy and sulfur present as inorganic sulfate measured by ion chromatography (IC) in fine particulate matter. These differences could be attributed to measurement bias and/or the contribution of other sulfur compounds, including organosulfates. Using the National Park Service IMPROVE PM(2.5) database, we examined the disparity between the sulfur and sulfate measurements at 12 sites across the United States to provide upper-bound estimates for the annual average contributions of organosulfates to organic mass. The data set consists of over 150000 measurements. The 12 sites include Brigantine, NJ, Cape Cod, MA, Washington, DC, Chassahowitzka, FL, Great Smoky Mountains National Park, NC, Okefenokee, GA, Bondville, IL, Mingo, MO, Phoenix, AZ, San Gabriel, CA, Crater Lake National Park, OR, and Spokane, WA. These sites are representative of the different regions of the country: Northeast, Southeast, Midwest, Southwest and Northwest. We estimate that organosulfur compounds could comprise as much as 5-10% of the organic mass at these sites. The contribution varies by season and location and appears to be higher during warm months when photochemical oxidation chemistry is most active.

Characterization of the Southwestern Desert Aerosol, Meadview, AZ

Sulfate, organic carbon, and soil dust were the major components of the fine aerosol at Meadview, AZ, during the summer of 1992. Sulfate mass median diameters (typically 0.15-0.27 μm) were much smaller than mass median diameters for organic carbon (typically 0.43-0.83 μm). Organic carbon size distributions were broader and more varied. Intersampler comparisons show that sulfur and sulfate measurement technology provided precise and relatively accurate (within 2-22%) concentrations. However, large differences were observed between IMPROVE filter and MOUDI impactor carbon concentrations. This is indicative of the large uncertainties with which carbon concentrations are measured. The IMPROVE backup filter subtraction procedure was partially responsible for these differences. Meadview sulfate was not completely neutralized by ammonium; SO2 concentrations were comparable to sulfate concentrations; and virtually all of the nitrate was present as gas-phase nitric acid. Our estimates suggest that primary organic aerosol from urban areas accounts for no more than 24% on average of the organic aerosol found at Meadview, AZ. The remainder is most likely secondary and biogenic OC, as well as OC from local and regional anthropogenic sources.

Pulmonary effects of inhaled diesel exhaust in aged mice

Pulmonary morbidity and mortality resulting from exposure to fine particulate matter (PM) increases with age. The present studies analyzed potential mechanisms underlying increased susceptibility of the elderly to PM using diesel exhaust (DE) as a model. Mice (2 m and 18 m) were exposed to DE (0, 300, and 1000 microg/m(3)) for 3 h once (single) or 3 h/day for 3 days (repeated). Bronchoalveolar lavage fluid (BAL), serum and lung tissue were collected 0 and 24 h later. Exposure to DE resulted in structural alterations in the lungs of older but not younger mice, including patchy thickening of the alveolar septa and inflammatory cell localization in alveolar spaces. These effects were most pronounced 24 h after a single exposure to the higher dose of DE. Significant increases in BAL nitrogen oxides were also noted in older mice, as well as expression of lipocalin 24p3, an oxidative stress marker in the lung with no effects in younger mice. Following DE inhalation, expression of Tumor Necrosis Factor alpha (TNFalpha) was upregulated in lungs of both younger and older mice; however, this was attenuated in older animals. Whereas exposure to DE resulted in increases in lung Interleukin-6 (IL-6) expression in both older and younger mice, IL-8 increased only in older animals. In younger mice, constitutive expression of manganese superoxide dismutase (MnSOD) decreased after DE exposure, while in older mice, constitutive MnSOD was not detectable and DE had no effect on expression of this antioxidant. Taken together, these results suggest that altered generation of inflammatory mediators and MnSOD may contribute to increased susceptibility of older mice to inhaled DE.

Microanalysis Methods for Characterization of Personal Aerosol Exposures

ABSTRACT Chemical characterization of particulate matter (PM) to which human populations are exposed is essential to developing an understanding of the risks and associations of PM with health endpoints. In this research we developed microanalysis methods for the characterization of personal exposure to PM and demonstrated the capabilities of sensitive analytical techniques through the analysis of 9 aerosol samples. These techniques will be used in future exposure assessment studies and to conduct source apportionment of personal and community exposures. Aerosol loadings comparable to 24-h personal exposure samples (150–480 μg) were collected on 25 mm Teflon filters with a PM10 personal sampler operating at 4 lpm. Qualitative functional group identification as well as quantitation of five metals (V, Cr, As, Cd, Pb) and 26 polycyclic aromatic hydrocarbons (PAHs) present in the aerosol samples was accomplished using the following techniques: Fourier Transform Infrared (FTIR) Spectroscopy, Inductively-Couple...

A closure study of extinction apportionment by multiple regression

Abstract Multiple regression has been widely used to apportion particle light scattering among distinct chemical species. The resulting scattering budgets are shown here to be unbiased estimates under certain theoretical conditions. The theory allows species’ particle size distributions and water uptakes to vary from sample to sample, as they are known to do in reality. The sole constraint is that variations in each species’ characteristics be statistically independent of all species’ concentrations. Individual violations of this condition cause identifiable biases, and multiple violations can offset each other to yield regression estimates that are accurate by accident. Detailed and summary accountings of statistical errors are illustrated using a mechanistic model derived from measurements in southern California.