Residential air exchange rates in three major US metropolitan areas: results from the Relationship Among Indoor, Outdoor, and Personal Air Study 1999-2001.

UNLABELLED: We report approximately 500 indoor-outdoor air exchange rate (AER) calculations based on measurements conducted in residences in three US metropolitan areas in 1999-2001: Elizabeth, New Jersey; Houston, Texas; and Los Angeles County, California. Overall, a median AER across these urban areas and seasons was 0.71 air changes per hour (ACH, or per hour; n = 509) while median AERs measured in California (n = 182), New Jersey (n = 163), and Texas (n = 164) were 0.87, 0.88, and 0.47 ACH, respectively. In Texas, the measured AERs were lower in the summer cooling season (median = 0.37 ACH) than in the winter heating season (median = 0.63 ACH), likely because of the reported use of room air conditioners as Houston is typically hot and humid during the summer. The measured AERs in California were higher in summer (median = 1.13 ACH) than in winter (median = 0.61 ACH). Because the summer cooling season in Los Angeles County is less humid than in New Jersey or Texas, natural ventilation through open windows and screened doors likely increased measured AER in California study homes. In New Jersey, AER were similar across heating and cooling seasons, although the median AER was relatively lower during the spring. PRACTICAL IMPLICATIONS: Adequate ventilation or air exchange rate (AER) for an indoor environment is important for human health and comfort, and relevant to building design and energy conservation and efficiency considerations. However, residential AER data, especially measured by more accurate non-toxic tracer gas methodologies, are at present quite limited worldwide, and are insufficient to represent the variations across regions and seasons within and between homes, including apartments and condominiums in more densely populated urban areas. The present paper presents quantitative and qualitative data to characterize residential AERs in three US urban areas with different climate attributes.

Evidence of inadequate ventilation in portable classrooms: results of a pilot study in Los Angeles County.

UNLABELLED: The prevalence of prefabricated, portable classrooms (portables) for United States public schools has increased; in California, approximately one of three students learn inside portables. Limited research has been conducted on indoor air and environmental quality in American schools, and almost none in portables. Available reports and conference proceedings suggest problems from insufficient ventilation due to poor design, operation, and/or maintenance of heating, ventilation and air conditioning (HVAC) systems; most portables have one mechanical, wall-mounted HVAC system. A pilot assessment was conducted in Los Angeles County, including measurements of integrated ventilation rates based on a perfluorocarbon tracer gas technique and continuous monitoring of temperature (T) and relative humidity (RH). Measured ventilation rates were low [mean school day integrated average 0.8 per hour (range: 0.1-2.9 per hour)]. Compared with relevant standards, results suggested adequate ventilation and associated conditioning of indoor air for occupant comfort were not always provided to these classrooms. Future school studies should include integrated and continuous measurements of T, RH, and ventilation with appropriate tracer gas methods, and other airflow measures. PRACTICAL IMPLICATIONS: Adequate ventilation has the potential to mitigate concentrations of chemical pollutants, particles, carbon dioxide, and odors in portable and traditional classrooms, which should lead to a reduction in reported health outcomes, e.g., symptoms of 'sick building syndrome', allergies, asthma. Investigations of school indoor air and environmental quality should include continuous temperature and relative humidity data with inexpensive instrumentation as indicators of thermal comfort, and techniques to measure ventilation rates.

Effects of fuel type, driving cycle, and emission status on in-use vehicle exhaust reactivity.

The introduction of reformulated gasolines significantly reduced exhaust hydrocarbon (HC) mass emissions, but few data are available concerning how these new fuels affect exhaust reactivity. Similarly, while it is well established that high-emitting vehicles contribute a significant portion of total mobile source HC mass emissions, it is also important to evaluate the exhaust reactivity from these vehicles. The objective of this study was to evaluate the relative influence on in-use vehicle exhaust reactivity of three critical factors: fuel, driving cycle, and vehicle emission status. Nineteen in-use vehicles were tested with seven randomly assigned fuel types and two driving cycles: the Federal Test Procedure (FTP) and the Unified Cycle (UC). Total exhaust reactivity was not statistically different between the FTP and UC cycles but was significantly affected by fuel type. On average, the exhaust reactivity for California Phase 2 fuel was the lowest (16% below the highest fuel type) among the seven fuels tested for cold start emissions. The average exhaust reactivity for high-emitting vehicles was significantly higher for hot stabilized (11%) and hot start (15%) emissions than for low-emitting vehicles. The exhaust reactivities for the FTP and UC cycles for light-end HCs and carbonyls were significantly different for the hot stabilized mode. There was a significant fuel effect on the mean specific reactivity (SR) for the mid-range HCs, but not for light-end HCs or carbonyls, while vehicle emission status affected the mean SR for all three HC compound classes.

Effects of grades and other loads on on-road emissions of hydrocarbons and carbon monoxide.

This project was developed to assess driving patterns that promote high emissions episodes, also known as emission excursions, particularly while driving on roads with grade. An instrumented vehicle was equipped to record driving conditions such as speed and grade, as well as measure emission rates of total hydrocarbons and carbon monoxide. Controlled runs with predetermined cruise speeds between 35 and 55 mph and accelerations less than 3.3 mph/second were conducted on flat terrain and on hills with grades ranging from 0 to 7%. The hills were located in metropolitan Los Angeles, both along freeways and arterial roads. For hydrocarbons, the increase in emissions was about 0.04 g/mile for each 1% grade increment. For carbon monoxide (CO), the increase was more dramatic: 3.0 g/mile for each 1% grade increment. For a fully occupied vehicle with four passengers on a 4.5% grade, emissions increased by 0.07 g/mile for hydrocarbons and 10.2 g/mile for CO. Air conditioning operation, at full setting, further increased emissions while driving on hills (4.5 and 6.7% grades) by 0.07 g/mile for hydrocarbons and 31.9 g/mile for CO.

Valuing the health benefits of clean air.

An assessment of health effects due to ozone and particulate matter (PM10) suggests that each of the 12 million residents of the South Coast Air Basin of California experiences ozone-related symptoms on an average of up to 17 days each year and faces an increased risk of death in any year of 1/10,000 as a result of elevated PM10 exposure. The estimated annual economic value of avoiding these effects is nearly $10 billion. Attaining air pollution standards may save 1600 lives a year in the region.

Biofiltration: an innovative air pollution control technology for VOC emissions.

Biofiltration is a relatively recent air pollution control (APC) technology in which off-gases containing biodegradable volatile organic compounds (VOC) or inorganic air toxics are vented through a biologically active material. This technology has been successfully applied in Germany and The Netherlands in many full-scale applications to control odors, VOC and air toxic emissions from a wide range of industrial and public sector sources. Control efficiencies of more than 90 percent have been achieved for many common air pollutants. Due to lower operating costs, biofiltration can provide significant economic advantages over other APC technologies if applied to off-gases that contain readily biodegradable pollutants in low concentrations. Environmental benefits include low energy requirements and the avoidance of cross media transfer of pollutants. This paper reviews the history and current status of biofiltration, outlines its underlying scientific and engineering principles, and discusses the applicability of biofilters for a wide range of specific emission sources.

Ubiquitous occurrence of 2-nitrofluoranthene and 2-nitropyrene in air.

Several nitrated polycyclic aromatic hydrocarbons (nitro-PAH) are direct-acting mutagens and/or carcinogens, and are important constituents of combustion emissions and ambient air. These nitro-PAH are emitted from various combustion sources including gasoline and diesel engine exhaust, aluminium smelting effluent, coal fly ash, wood smoke, and cigarette smoke condensates. Of these, diesel engine exhaust is the best characterized, more than 50 nitrated polycyclic aromatic compounds having been identified by Paputa-Peck et al., including 1-nitropyrene (1-NP) as the single most abundant nitro-PAH. However, nitro-PAH may also be formed during source-receptor transport by atmospheric reactions of adsorbed or gas-phase PAH with oxides of nitrogen, nitric acid and other atmospherically important species such as the OH radical. Evidence for the atmospheric formation of nitro-PAH has come only recently, from observations that 2-nitropyrene (2-NP) and 2-nitrofluoranthene (2-NF) neither of which has been reported to be emitted from combustion sources, are among the major nitro-PAH present in ambient air. We present here data from several locations which demonstrate that these two atmospherically formed nitro-PAH are ubiquitous in tropospheric ambient air.

Gaseous nitrate radical: possible nighttime atmospheric sink for biogenic organic compounds.

The gaseous nitrate (NO(3)) radical, which has recently been measured in nighttime ambient atmospheres over the United States and Europe at concentrations up to approximately 350 parts per trillion, has now been shown to react rapidly with the biogenically emitted organic compounds dimethyl sulfide (DMS), isoprene, and several monoterpenes. Computer simulations demonstrate that these reactions can dominate the atmospheric behavior of these organic compounds at night. Thus reaction with NO(3) radicals may be the unknown, nonphotochemical removal process for DMS recently invoked by Andreae and Raemdonck to explain the absence of a diurnal profile for DMS in maritime air influenced by continental air masses. Similarly, the nighttime reaction of NO(3) radicals with monoterpenes can be a dominant removal process, leading to very low monoterpene concentrations in ambient atmospheres during the early morning.

Trace nitrogenous species in urban atmospheres.

Recent results concerning the identification and measurement of nitrogenous air pollutants in the California South Coast Air Basin (CSCAB) are presented. In planning or evaluating studies of the human health effects of these pollutants, it is important to consider the entire range of species which may be present. We provide estimates of typical exposures to nitrogenous air pollutants during a single day oxidant event in the CSCAB.