Kabindra M. Shakya

Secondary organic aerosol from photooxidation of polycyclic aromatic hydrocarbons.

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.

Lignin-derived phenols in Houston aerosols: implications for natural background sources.

Solvent-extractable monomeric methoxyphenols in aerosol samples conventionally have been used to indicate the influence of biomass combustion. In addition, the presence of lignin oxidation products (LOP), derived from the CuO oxidation of vascular plant organic matter, can help trace the source and inputs of primary biological particles in aerosols. Ambient aerosols (coarse and fine) collected in Houston during summer 2010 were analyzed by gas chromatography-mass spectrometry to characterize monomeric and polymeric sources of LOPs. This is the first time polymeric forms of the LOPs have been characterized in ambient aerosols. The absence or small concentrations of solvent-extractable monomeric LOPs and levoglucosan isomers point to the limited influence of biomass burning during the sampling period. The trace levels of anhydrosugar concentrations most likely result from long-range transport. This observation is supported by the absence of co-occurring lignin monomers that undergo photochemical degradation during transport. The larger concentration (142 ng m(-3)) of lignin polymers in coarse aerosols shows the relative importance of primary biological aerosol particles, even in the urban atmosphere. The LOP parameters suggest a predominant influence from woody tissue of angiosperms, with minor influence from soft tissues, gymnosperms, and soil organic matter.

Investigating missing sources of sulfur at Fairbanks, Alaska.

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.

Respiratory Effects of High Levels of Particulate Exposure in a Cohort of Traffic Police in Kathmandu, Nepal.

Objectives: To investigate the traffic-related PM2.5 and black carbon (BC) exposures and assess their health effects. Methods: Personal exposure to PM2.5 and BC levels were monitored in a cohort of traffic police (n = 53) at six locations in Kathmandu Valley, Nepal during dry and rainy seasons in 2014. Results: Mean on-road exposure levels of PM2.5 and BC ranged from 34 to 193 &mgr;g/m3 and 12 to 28 &mgr;gC/m3, respectively, and were associated with an acute decline in lung function. Use of N95 mask had clear benefits reducing the lung function decreases after occupational exposures when masks were worn for just half of a workweek. Conclusions: Exposure of high levels of PM2.5 was associated with reduced lung function. Increased levels of BC exposure led to reduced lung function in non-smoking traffic officers with non-normal spirometry observations.

Evaluating the efficacy of cloth facemasks in reducing particulate matter exposure

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.