Inexpensive cloth masks are widely used in developing countries to protect from particulate pollution albeit limited data on their efficacy exists. This study examined the efficiency of four types of masks (three types of cloth masks and one type of surgical mask) commonly worn in the developing world. Five monodispersed aerosol sphere size (30, 100, and 500 nm, and 1 and 2.5 μm) and diluted whole diesel exhaust was used to assess facemask performance. Among the three cloth mask types, a cloth mask with an exhaust valve performed best with filtration efficiency of 80-90% for the measured polystyrene latex (PSL) particle sizes. Two styles of commercially available fabric masks were the least effective with a filtration efficiency of 39-65% for PSL particles, and they performed better as the particle size increased. When the cloth masks were tested against lab-generated whole diesel particles, the filtration efficiency for three particle sizes (30, 100, and 500 nm) ranged from 15% to 57%. Standard N95 mask performance was used as a control to compare the results with cloth masks, and our results suggest that cloth masks are only marginally beneficial in protecting individuals from particles<2.5 μm. Compared with cloth masks, disposable surgical masks are more effective in reducing particulate exposure.

Secondary organic aerosol (SOA) formation from the photooxidation of five polycyclic aromatic hydrocarbons (PAHs, naphthalene, 1- and 2-methylnaphthalene, acenaphthylene, and acenaphthene) was investigated in a 9-m(3) chamber in the presence of nitrogen oxides and the absence of seed aerosols. Aerosol size distributions and PAH decay were monitored by a scanning mobility particle sizer and a gas chromatograph with a flame ionization detector. Over a wide range of conditions, the aerosol yields for the investigated PAHs were observed to be in the range of 2-22%. The observed evolution of aerosol and PAH decay indicate that light and oxidant sources influence the time required to form aerosol and the required threshold reacted concentration of the PAHs. The SOA yields also were related to this induction period and the hydroxyl radical concentrations, particularly for smaller aerosol loadings (<∼6 μg m(-3)). Estimation of SOA production from oxidation of PAHs emitted from mobile sources in Houston shows that PAHs could account for more than 10% of the SOA formed from emissions from mobile sources in this region.

We investigated disparities in elemental sulfur and inorganic sulfate concentrations in ambient fine particulate matter (PM2.5) data from 2005 to 2012 at a monitoring station in Fairbanks, AK. In approximately 28% of the observations from 2005 to 2012, elemental sulfur by X-ray fluorescence (XRF) spectroscopy significantly exceeded the inorganic sulfur by ion chromatography (IC), suggesting the presence of a significant quantity of unmeasured sulfur compounds. The mean ratio of sulfur by XRF to that by IC for only these cases was 1.22 ± 0.11. The largest discrepancies between elemental sulfur and sulfate were most frequently observed in the summer, although discrepancies were observed year round. Assuming the additional sulfur (other than inorganic sulfate) as the upper limit estimate, this work shows that organosulfur species (or the additional sulfur) account for 1.29% of organic carbon (OC) and 0.75% of PM2.5 in Fairbanks. An analysis of all available air quality system (AQS) data suggests that these recurring phenomena are linked to seasons, total carbon, inorganic nitrate, and elemental sources during cold periods and ozone during warm periods.

To investigate the air pollution from aerosols in Kathmandu during winter, bulk aerosol samples were collected during winter [2007][2008] to characterize carbonaceous and ionic species and carbon and nitrogen isotopes. This study illustrates the applications of carbon and nitrogen isotope data for characterizing aerosols and their implications for identifying sources that were inconsistent with the results for the carbonaceous and ionic aerosols. Mean concentrations of organic carbon (OC), elemental carbon (EC), and water soluble organic carbon (WSOC) in Kathmandu during the period were 20.02 ± 6.59 (1σ), 4.48 ± 1.17, and 10.09 ± 3.64 µgC/m 3 , respectively. Elemental carbon and OC were correlated (R 2 = 0.56), likely indicating common sources for both species, as well as for the precursors that led to the formation of secondary organic carbon (SOC). The mean estimated SOC contribution to OC was 31%, suggesting that local emission is more important than transport and processing during winter in Kathmandu. On average, 50% of the OC was water soluble, and the correlation of SOC with WSOC (R 2 = 0.66) suggests that the majority of SOC and some primary organic carbon (POC) were water soluble in Kathmandu. The mean δ 13 C of -25.74 ± 0.19‰ observed in aerosols of Kathmandu confirms consistent anthropogenic sources such as fossil fuel combustion. Heavier carbon also was observed to be associated with the water-soluble fraction of OC in aerosols. The mean δ 15 N of 9.45 ± 0.87‰ suggests the limited influence of biomass burning and its strong correlation with crustal cations Ca 2+ (R 2 = 0.74, p < 0.05) and Mg 2+ (R 2 = 0.71, p < 0.05) indicates distant sources. Principal component analysis revealed four major sources/pathways for particles: local and vehicular emissions, secondary gas-to-particle conversion, aqueous processing, and dust transport, each explaining ~39, 23, 11, and 9% of the variance.