Pollutant emission rates from indoor combustion appliances and sidestream cigarette smoke

Particulate and gaseous emissions from indoor combustion appliances and smoking can elevate the indoor concentrations of various pollutants. Indoor pollutant concentrations resulting from operating one of several combustion appliances, or from sidestream tobacco smoke, were measured in a 27-m³ environmental chamber under varying ventilation rates. The combustion appliances investigated were gas-fired cooking stoves, unvented kerosene-fired space heaters, and unvented natural-gas-fired space heaters. Results showed elevated levels of carbon dioxide, carbon monoxide, nitric oxide, nitrogen dioxide, formaldehyde, and suspended particles from one or more of the pollutant sources investigated. Our findings suggest that, of the sources examined in this study, nitrogen dioxide from combustion appliances and particles from sidestream cigarette smoke are the most serious contaminants of indoor air, if we use existing standards and guidelines as the criteria. An emission rate model was used to quantify the strengths of the pollutant sources, which are reported in terms of the mass of pollutant emitted per energy unit of fuel consumed (in the case of gas and kerosene appliances) and per mass of tobacco combusted (in the case of smoking).     

USA tackles critical materials

The USA is heavily dependent on foreign sources for supplies of key materials essential to the nation's defence and to the operation of its vital industries. For example, it depends on foreign sources for 22 of the 27 metals considered vital to the country's economy. A public workshop on Conservation and Substitution Technology for Critical Materials was held from 15–17 June 1981 at Vanderbilt University, Nashville, Tennesse, to examine national policies towards resolving the supply problems associated with chromium, cobalt, tantalum and titanium.     

Method comparisons for particulate nitrate, elemental carbon, and PM2.5 mass in seven U.S. cities

Methods that measure PM2.5 mass, total particulate NO3-, and elemental carbon (EC) were evaluated in seven U.S. cities from 1997 to 1999. Sampling was performed in Bakersfield, CA; Boston, MA; Chicago, IL; Dallas, TX; Philadelphia, PA; Phoenix, AZ; and Riverside, CA. Evaluating and validating methods that measure the components of fine mass are important to the effort of establishing a speciation-monitoring network. The Harvard Impactor (HI), which measures fine particle mass, showed excellent agreement (r2 = 0.99) with the PM2.5 Federal Reference Method (FRM) for 81 24-hr samples in Riverside and Bakersfield. The HI also showed good precision (4.8%) for 243 24-hr collocated samples over eight studies. The Aethalometer was employed in six of the sampling locations to measure black carbon (BC). These values were compared to EC as measured from a quartz filter using thermal analysis. For the six cities combined, the two methods were highly correlated (r2 = 0.94; 187 24-hr samples); however, the BC values were approximately 24% less than the EC measurements consistently across all six cites. This compares well to results observed for EC/BC measurements observed in other semi-urban areas. Particulate NO3- was measured using the Harvard-EPA Annular Denuder System (HEADS). This was compared to the NO3- measured from the HI Teflon (DuPont) filter to assess NO3- artifacts. Significant NO3- losses (approximately 50% of total NO3-) were found in Riverside, Philadelphia, and Boston, while minimal artifacts were observed in the other sites. Two types of HEADS configurations were employed in five cities. One system used a Na2CO3-coated glass fiber filter, and the other type used a nylon filter to collect volatilized NO3- from the Teflon filter. The HEADS with the Na2CO3-coated filter consistently underestimated the total particulate NO3- by approximately 20% compared to the nylon HEADS.     

Short-term temporal variation in PM2.5 mass and chemical composition during the Atlanta Supersite Experiment, 1999

Measurements in urban Atlanta of transient aerosol events in which PM2.5 mass concentrations rapidly rise and fall over a period of 3-6 hr are reported. The data are based on new measurement techniques demonstrated at the U.S. Environmental Protection Agency (EPA) Atlanta Supersite Experiment in August 1999. These independent instruments for aerosol chemical speciation of NO3-, SO4(2-), NH4+, and organic and elemental carbon (OC and EC), reconstructed the observed hourly dry PM2.5 mass to within 20% or better. Data from the experiment indicated that transient PM2.5 events were ubiquitous in Atlanta and were typically characterized by a sudden increase of EC (soot) and OC in the early morning or SO4(2-) in the late afternoon. The frequent temporal decoupling of these events provides insights into their origins, suggesting mobile sources in metro Atlanta as the main contributor to early morning PM2.5 and more regionally located point SO2 sources for afternoon PM2.5 events. The transient events may also have health implications. New data suggest that short-term PM2.5 exposures may lead to adverse health effects. Standard integrated filter-based techniques used in PM2.5 compliance monitoring networks and in most past PM2.5 epidemiologic studies collect samples over 24-hr periods and thus are unable to capture these transient events. Moreover, health-effects studies that focus on daily PM2.5 mass alone cannot evaluate the health implications of the unique and variable chemical properties of these episodes.     

An evaluation of ozone exposure metrics for a seasonally drought-stressed ponderosa pine ecosystem

Ozone stress has become an increasingly significant factor in cases of forest decline reported throughout the world. Current metrics to estimate ozone exposure for forest trees are derived from atmospheric concentrations and assume that the forest is physiologically active at all times of the growing season. This may be inaccurate in regions with a Mediterranean climate, such as California and the Pacific Northwest, where peak physiological activity occurs early in the season to take advantage of high soil moisture and does not correspond to peak ozone concentrations. It may also misrepresent ecosystems experiencing non-average climate conditions such as drought years. We compared direct measurements of ozone flux into a ponderosa pine canopy with a suite of the most common ozone exposure metrics to determine which best correlated with actual ozone uptake by the forest. Of the metrics we assessed, SUM0 (the sum of all daytime ozone concentrations > 0) best corresponded to ozone uptake by ponderosa pine, however the correlation was only strong at times when the stomata were unconstrained by site moisture conditions. In the early growing season (May and June). SUM0 was an adequate metric for forest ozone exposure. Later in the season, when stomatal conductance was limited by drought. SUM0 overestimated ozone uptake. A better metric for seasonally drought-stressed forests would be one that incorporates forest physiological activity, either through mechanistic modeling, by weighting ozone concentrations by stomatal conductance, or by weighting concentrations by site moisture conditions.     

A cost-effective weighing chamber for particulate matter filters

Particulate matter (PM) is a ubiquitous air pollutant that has been receiving increasing attention in recent years due in part to the association between PM and a number of adverse health outcomes, including mortality and increases in emergency room visits and respiratory symptoms, as well as exacerbation of asthma and decrements in lung function. As a result, the ability to accurately sample ambient PM has become important, both to researchers and to regulatory agencies. The federal reference method for the determination of fine PM as PM2.5 in the atmosphere recommends that particle-sampling filters be conditioned and weighed in an environment with constant temperature and relative humidity (RH). It is also recommended that vibration, electrostatic charges, and contamination of the filters from laboratory air be minimized to reduce variability in filter weight measurements. These controls have typically been maintained in small, environmentally controlled "cleanrooms." As an alternative to constructing an elaborate cleanroom, we have designed, and presented in this paper, an inexpensive weighing chamber to maintain the necessary level of humidity control.     

A review of the export of carbon in river water: fluxes and processes

This review summarizes data on exports of carbon from a large number of temperate and boreal catchments in North America, Europe and New Zealand. Organic carbon losses, usually dominated by dissolved organic matter, show relatively little variation, most catchments exporting between 10 and 100 kg C ha(-1) yr(-1). Inorganic carbon exports occur at a similar rate. However, a lack of information on the flux of particulate organic carbon and dissolved CO2 is highlighted, particularly for rivers in Europe. Processes regulating the flux of organic carbon to streams and its subsequent fate in-stream are reviewed, along with the effects of land use and acidification on these processes. The size of the global riverine flux of carbon in relation to the global carbon cycle and the possible effects of environmental change on the export of carbon in rivers are considered.