Secular trends of atmospheric methane (CH4)

Due partly to human activities the present yearly emissions of CH₄ exceed the atmospheric sinks, thus leading to a 1.2–1.9% per year atmospheric increase in the concentration of CH₄. New evidence based on studies of polar ice cores suggests that several hundred years ago the concentrations of CH₄ were perhaps only half of current values. These diverse findings are tied together in a single unified logistic model of atmospheric concentrations past, present and future. Using realistic growth rates of the sources of CH₄ caused by human activities, the model explains the concentrations and current growth rates. It also predicts that a doubling of CH₄ relative to present levels is possible given the long (9-year) atmospheric lifetime. Such increases of CH₄ concentrations may have already perturbed our global environment and may continue to do so in the future. The environmental effects include increased surface temperature of the earth, additional O₃ and CO in the clean non-urban atmosphere, depletions of tropospheric OH radicals, but perhaps also protection of the stratospheric ozone layer from destruction by man-made fluorocarbons.     

Measuring visual opacity using digital imaging technology

The U.S. Environmental Protection Agency (EPA) Reference Method 9 (Method 9) is the preferred enforcement approach for verifying facility compliance with federal visible opacity standards. Supporters of Method 9 have cited its flexibility and low cost as important technological and economic advantages of the methodology. The Digital Opacity Compliance System (DOCS), an innovative technology that employs digital imaging technology for quantifying visible opacity, has been proposed as a technically defensible and economically competitive alternative to Method 9. Results from the field application of the DOCS at EPA-approved Method 9 smoke schools located in Ogden, UT, Augusta, GA, and Columbus, OH, demonstrated that, under clear sky conditions, the DOCS consistently met the opacity error rate established under Method 9. Application of hypothesis testing on the smoke school data set confirmed that the DOCS was equivalent to Method 9 under clear sky conditions. Under overcast sky conditions, human observers seemed to be more accurate than the DOCS in measuring opacity. However, within the smoke school environment, human observers routinely employ backgrounds other than sky (e.g., trees, telephone poles, billboards) to quantify opacity on overcast days. Under conditions that compel the use of sky as plume background (e.g., emission stacks having heights above the tree line), the DOCS appears to be a more accurate methodology for quantifying opacity than are human observers.     

Carbon Monoxide in an Urban Environment: Application of a Receptor Model for Source Apportionment

During the winter of 1985-86 the authors took 6-h integrated air samples and measured the concentrations of carbon monoxide and other gases at a residential site in Olympia, Washington. The 6-h average concentrations were between about 0.2 and 3.2 ppmv. For each 6-h period the observed concentration of CO was apportioned among its sources which were residential wood burning and automobiles. Small and generally insignificant amounts of CO were also observed from unidentified sources. A chemical mass balance (CMB) was formulated and applied to apportion the observed CO among its sources. Methylchloride (CH₃CI), in excess of background levels, was used as a unique tracer of wood burning and excess hydrogen (H₂) served as a tracer of CO from automobiles. The source emission factors to carry out the calculations were estimated from other experiments. The results showed that in Olympia, wood burning can often contribute as much CO as automobiles during winter. The maximum 6-h average contribution of CO from wood burning was about 2 ppmv and from automobiles it was 2.2 ppmv, and the average ambient concentration was about 1 ppmv. When pollution from wood burning was present, it contributed 0.5 ppmv on average while automobiles also contributed 0.5 ppmv. Unidentified sources contributed 0.1 ppmv and the background level was 0.15 ppmv. During the winter many times wood burning did not affect CO concentrations, while CO from automobiles was always present. On average, during the winter, automobiles contributed some 50 percent of the CO mass to the lower urban atmosphere and wood burning contributed about 30 percent. Diurnal cycles became evident in the calculated concentrations of CO from wood burning and automobiles even though the measured concentrations did not show strong diurnal variations. Wood burning contributed most during evening and nighttime and very little during the day, while automobiles contributed most during the morning and evening hours and very little at night. These patterns lend support to the accuracy of the model and source emission factors since they are as expected from the diurnal variations of the sources and atmospheric mixing.     

Effect of Fuel Properties on Mutagenic Activity in Extracts of Heavy-duty Diesel Exhaust Particulate

The effect of varying fuel properties on the emission of mutagenic materials was studied in diesel exhaust particles from a heavy duty engine run under transient speed and load conditions while using nine fuels varying in aromatics, sulfur and boiling point. Mutagenic activity of the soluble organic fraction (SOF) of the particulate was determined using the Ames Salmonella test system with strain TA98 with and without S9 activation. Increasing mutagenic activity relative to fuel consumed (mutants/lb fuel) or to engine work output (mutants/hp-h) was correlated with increasing fuel aromatics (p < 0.05), but not with fuel sulfur. Increased fuel sulfur levels were correlated with increased amounts of SOF but with decreasing mutagenic activity of the SOF (mutants/microgram SOF) (p < 0.05). As a result, mutants/hp-h were essentially the same for high- and low-sulfur fuels with high aromatics. No association was found between the fuels’ boiling points and the mutagenic activity of the SOF. Mutagenic activity with S9 was generally lower than without, but the correlations were not changed.     

Lead speciation in indoor dust: a case study to assess old paint contribution in a Canadian urban house

Residents in older homes may experience increased lead (Pb) exposures due to release of lead from interior paints manufactured in past decades, especially pre-1960s. The objective of the study was to determine the speciation of Pb in settled dust from an urban home built during WWII. X-ray absorption near-edge structure (XANES) and micro-X-ray diffraction (XRD) analyses were performed on samples of paint (380–2,920 mg Pb kg⁻¹) and dust (200–1,000 mg Pb kg⁻¹) collected prior to renovation. All dust samples exhibited a Pb XANES signature similar to that of Pb found in paint. Bulk XANES and micro-XRD identified Pb species commonly found as white paint pigments (Pb oxide, Pb sulfate, and Pb carbonate) as well as rutile, a titanium-based pigment, in the <150 μm house dust samples. In the dust fraction <36 μm, half of the Pb was associated with the Fe-oxyhydroxides, suggesting additional contribution of outdoor sources to Pb in the finer dust. These results confirm that old paints still contribute to Pb in the settled dust for this 65-year-old home. The Pb speciation also provided a clearer understanding of the Pb bioaccessibility: Pb carbonate > Pb oxide > Pb sulfate. This study underscores the importance of taking precautions to minimize exposures to Pb in house dust, especially in homes where old paint is exposed due to renovations or deterioration of painted surfaces.