Will Ollison

A pilot study using scripted ventilation conditions to identify key factors affecting indoor pollutant concentration and air exchange rate in a residence

A pilot study was conducted using an occupied, single-family test house in Columbus, OH, to determine whether a script-based protocol could be used to obtain data useful in identifying the key factors affecting air-exchange rate (AER) and the relationship between indoor and outdoor concentrations of selected traffic-related air pollutants. The test script called for hourly changes to elements of the test house considered likely to influence air flow and AER, including the position (open or closed) of each window and door and the operation (on/off) of the furnace, air conditioner, and ceiling fans. The script was implemented over a 3-day period (January 30–February 1, 2002) during which technicians collected hourly-average data for AER, indoor, and outdoor air concentrations for six pollutants (benzene, formaldehyde (HCHO), polycyclic aromatic hydrocarbons (PAH), carbon monoxide (CO), nitric oxide (NO), and nitrogen oxides (NOx)), and selected meteorological variables. Consistent with expectations, AER tended to increase with the number of open exterior windows and doors. The 39 AER values measured during the study when all exterior doors and windows were closed varied from 0.36 to 2.29 h−1 with a geometric mean (GM) of 0.77 h−1 and a geometric standard deviation (GSD) of 1.435. The 27 AER values measured when at least one exterior door or window was opened varied from 0.50 to 15.8 h−1 with a GM of 1.98 h−1 and a GSD of 1.902. AER was also affected by temperature and wind speed, most noticeably when exterior windows and doors were closed. Results of a series of stepwise linear regression analyses suggest that (1) outdoor pollutant concentration and (2) indoor pollutant concentration during the preceding hour were the “variables of choice” for predicting indoor pollutant concentration in the test house under the conditions of this study. Depending on the pollutant and ventilation conditions, one or more of the following variables produced a small, but significant increase in the explained variance (R2-value) of the regression equations: AER, number and location of apertures, wind speed, air-conditioning operation, indoor temperature, outdoor temperature, and relative humidity. The indoor concentrations of CO, PAH, NO, and NOx were highly correlated with the corresponding outdoor concentrations. The indoor benzene concentrations showed only moderate correlation with outdoor benzene levels, possibly due to a weak indoor source. Indoor formaldehyde concentrations always exceeded outdoor levels, and the correlation between indoor and outdoor concentrations was not statistically significant, indicating the presence of a strong indoor source.

Sensitive measurement of ozone using amperometric gas sensors

We have investigated the ability of miniature amperometric gas sensors (AGS) to detect ozone in air at concentrations as low as 5 ppb. Baseline drift of the sensor, which occurs on a time scale of hours, can be compensated by periodic correction using sample air scrubbed free of oxidants. Interfering gases expected are nitrogen dioxide and nitrous acid. The latter can be removed with a sodium carbonate-glycerol filter, but a chemical filter that can remove nitrogen dioxide in the presence of ozone is not known. However, filters containing indigo can be used to remove ozone from an air stream without affecting the NO2. Selective and sensitive measurement of ozone was achieved by using two matched sensors connected in series, with an indigo filter between. The first sensor measured ozone plus nitrogen dioxide, whereas the second sensor was exposed only to NO2. The ozone signal is the difference in the two signals.

A re-examination of ambient air ozone monitor interferences.

Abstract Attaining the National Ambient Air Quality Standard (NAAQS) for ozone (O3) could cost billions of dollars nationwide. Attainment of the NAAQS is judged on O3 measurements made by the Federal Reference Method (FRM), ethylene chemiluminescence, or a Federal Equivalent Method (FEM), predominantly ultraviolet (UV) absorption. Starting in the 1980s, FRM monitors were replaced by FEMs so that today virtually all monitoring in the United States uses the UV methodology. This report summarizes a laboratory and collocated ambient air monitoring study of interferences in O3 monitors. Potential interferences examined in the laboratory included water vapor, mercury, o-nitrophenol, naphthalene, p-tolualdehyde, and mixed reaction products from smog chamber simulations of urban atmospheric photochemistry. UV absorption O3 monitors modified for humidity equilibration were also collocated with UV FEM O3 monitors at six sites in Houston, TX, during the 2007 summer O3 season. The results suggest that humidity and interfering species can positively bias (overestimate) O3 measured by FEM monitors used to determine compliance with the O3 standards. The results also suggest that humidity equilibration can mitigate this bias.

Continuous Monitoring of Particle Emissions during Showering

Abstract Particle formation from showering may be attributed to dissolved mineral aerosols remaining after evaporation of micron-sized satellite droplets produced by the shower-head or from splashing of larger shower water droplets on surfaces. Duplicate continuous particle monitors measured particle size distributions in a ventilated residential bathroom under various showering conditions, using a full-size mannequin in the shower to simulate splashing effects during showering. Particle mass concentrations were estimated from measured shower particle number densities and used to develop emission factors for inhalable particles. Emission source strengths of 2.7–41.3 μg/m3/min were estimated under the various test conditions using residential tap water in Columbus, OH. Calculated fine particulate matter (PM2.5) concentrations in the bathroom reached several hundred micrograms per cubic meter; calculated coarse particulate matter (PM10) levels approached 1000 μg/m3. Rates of particle formation tended to be highest for coarse shower spray settings with direct impact on the mannequin. No consistent effects of water temperature, water pressure, or spray setting on overall emission rates were apparent, although water temperature and spray setting did have an effect when varied within a single shower sampling run. Salt solutions were injected into the source water during some tests to assess the effects of total dissolved solids on particle emission rates. Injection of salts was shown to increase the PM2.5 particle formation rate by approximately one third, on average, for a doubling in tap water-dissolved solids content; PM10 source strengths approximately doubled under these conditions, because very few particles >10 μm were formed.

Prediction of hourly microenvironmental concentrations of fine particles based on measurements obtained from the Baltimore scripted activity study

Researchers have developed a variety of computer-based models to estimate population exposure to air pollution. These models typically estimate exposures by simulating the movement of specific population groups through defined microenvironments. During the summer of 1998 and winter of 1999, researchers with the Harvard School of Public Health (HSPH) conducted a field study in Baltimore, MD, to acquire data for improving microenvironmental models. Using a special roll-around instrument system, a technician measured 1- and 12-h pollutant concentrations while engaging in scripted sequences of activities typical of retirees. Each scripted activity assigned the technician to a geographic location and to a microenvironment. The technician recorded special conditions associated with each activity (e.g., open windows, environmental tobacco smoke) in a real-time diary. Data on ambient pollutant levels, temperature, and other potential explanatory factors were also collected. Eleven pollutants were measured by the roll-around instrument system, including particulate matter with an aerodynamic diameter less than 2.5 µm (PM2.5), ozone, carbon monoxide, and benzene. This article presents the results of statistical analyses performed solely on the 1-h PM2.5 data measured by a DustTrak monitor, which ranged from 1.5 to 444.8 µg/m3 with a median value of 14.6 µg/m3. Results of stepwise linear regression (SLR) suggest that PM2.5 exposure is significantly increased by passive smoking, high ambient PM2.5 concentrations reported by fixed-site monitors, food preparation, charcoal grills, car travel, outdoor roadside locations, and high humidity. Analysts should explicitly represent the effects of these parameters within any model developed to estimate population exposure to PM2.5. In a related study, a panel of volunteer retirees each carried a personal PM2.5 monitor and a real-time diary for nominal 24-h sampling periods as they engaged in normal daily activities. A regression equation derived from SLR analysis of the scripted activity database was applied to eight subject-days of diary data provided by the volunteer seniors to produce estimates of PM2.5 exposure for each event documented in each diary. The event-specific exposure estimates were then averaged over all events in each sampling period to produce nominal 24-h average exposure estimates. The absolute difference between the estimate obtained from the regression equation and the corresponding personal monitor measurement averaged 13%. The fixed-site monitors generally provided poorer estimates of exposure; the absolute differences for the Old Town and Clifton Park monitors averaged 26.7% and 19.5%, respectively, of the personal monitor values.

Relationships of attached garage and home exposures to fuel type and emission levels of garage sources

Mobile source air toxics (MSAT) may pose an adverse health risk, especially in microenvironments with high exposures to vehicle exhaust or evaporative emissions. Although programs such as reformulated gasoline are intended to reduce the emissions of MSAT and ozone precursors, uncertainties remain regarding population exposures associated with both oxygenate-gasoline blends and conventional gasoline. Measurements were carried out in San Antonio, Texas under controlled conditions to establish relationships between vehicle tailpipe and evaporative emissions and concentration levels in a residence with an attached garage. This paper concentrates on the influence of vehicle type (sedan versus pickup truck), its operational mode (normal versus malfunction), and fuel type (conventional versus oxygenated) on the pollutant levels in the attached garage and adjacent room (kitchen).

Concentrations of mobile source air pollutants in urban microenvironments

Human exposures to criteria and hazardous air pollutants (HAPs) in urban areas vary greatly due to temporal-spatial variations in emissions, changing meteorology, varying proximity to sources, as well as due to building, vehicle, and other environmental characteristics that influence the amounts of ambient pollutants that penetrate or infiltrate into these microenvironments. Consequently, the exposure estimates derived from central-site ambient measurements are uncertain and tend to underestimate actual exposures. The Exposure Classification Project (ECP) was conducted to measure pollutant concentrations for common urban microenvironments (MEs) for use in evaluating the results of regulatory human exposure models. Nearly 500 sets of measurements were made in three Los Angeles County communities during fall 2008, winter 2009, and summer 2009. MEs included in-vehicle, near-road, outdoor, and indoor locations accessible to the general public. Contemporaneous 1- to 15-min average personal breathing zone concentrations of carbon monoxide (CO), carbon dioxide (CO2), volatile organic compounds (VOCs), nitric oxide (NO), nitrogen oxides (NOx), particulate matter (<2.5 μm diameter; PM2.5) mass, ultrafine particle (UFP; <100 nm diameter) number, black carbon (BC), speciated HAPs (e.g., benzene, toluene, ethylbenzene, xylenes [BTEX], 1,3-butadiene), and ozone (O3) were measured continuously. In-vehicle and inside/outside measurements were made in various passenger vehicle types and in public buildings to estimate penetration or infiltration factors. A large fraction of the observed pollutant concentrations for on-road MEs, especially near diesel trucks, was unrelated to ambient measurements at nearby monitors. Comparisons of ME concentrations estimated using the median ME/ambient ratio versus regression slopes and intercepts indicate that the regression approach may be more accurate for on-road MEs. Ranges in the ME/ambient ratios among ME categories were generally greater than differences among the three communities for the same ME category, suggesting that the ME proximity factors may be more broadly applicable to urban MEs. Implications: Estimates of population exposure to air pollutants extrapolated from ambient measurements at ambient fixed site monitors or exposure surrogates are prone to uncertainty. This study measured concentrations of mobile source air toxics (MSAT) and related criteria pollutants within in-vehicle, outdoor near-road, and indoor urban MEs to provide multipollutant ME measurements that can be used to calibrate regulatory exposure models.

Potential Interference Bias in Ozone Standard Compliance Monitoring

Abstract The U.S. Environmental Protection Agency has established a federal reference method (FRM) for ozone (O3) and allowed for designation of federal equivalent methods (FEMs). However, the ethylene‐chemiluminescence FRM for O3 has been replaced by the UV photometric FEM by most state and local monitoring agencies because of its relative ease of operation. Accumulating evidence indicates that the FEM is prone to bias under the hot, humid, and stagnant conditions conducive to high O3 formation. This bias may lead to overreporting hourly O3 concentrations by as much as 20–40 ppb. Measurement bias is caused by contamination of the O3 scrubber, a problem that is not detected by dry air calibration. An adequate wet test has not been codified, although a procedure has been proposed for agency consideration. This paper includes documentation of laboratory tests quantifying specific interferant responses, collocated ambient FRM/FEM monitoring results, and smog chamber comparisons of the FRM and FEMs with alternative scrubber designs. As the numbers of reports on monitor interferences have grown, interested parties have called for agency recognition and correction of these biases.

Field testing of new-technology ambient air ozone monitors

Multibillion-dollar strategies control ambient air ozone (O3) levels in the United States, so it is essential that the measurements made to assess compliance with regulations be accurate. The predominant method employed to monitor O3 is ultraviolet (UV) photometry. Instruments employ a selective manganese dioxide or heated silver wool “scrubber” to remove O3 to provide a zero reference signal. Unfortunately, such scrubbers remove atmospheric constituents that absorb 254-nm light, causing measurement interference. Water vapor also interferes with the measurement under some circumstances. We report results of a 3-month field test of two new instruments designed to minimize interferences (2B Technologies model 211; Teledyne-API model 265E) that were operated in parallel with a conventional Thermo Scientific model 49C O3 monitor. The field test was hosted by the Houston Regional Monitoring Corporation (HRM). The model 211 photometer scrubs O3 with excess nitric oxide (NO) generated in situ by photolysis of added nitrous oxide (N2O) to provide a reference signal, eliminating the need for a conventional O3 scrubber. The model 265E analyzer directly measures O3–NO chemiluminescence from added excess NO to quantify O3 in the sample stream. Extensive quality control (QC) and collocated monitoring data are assessed to evaluate potential improvements to the accuracy of O3 compliance monitoring. Implications: Two new-technology ozone monitors were compared with a conventional monitor under field conditions. Over 3 months the conventional monitor reported more exceedances of the current standard than the new instruments, which could potentially result in an area being misjudged as “nonattainment.” Instrument drift can affect O3 data accuracy, and the same degree of drift has a proportionally greater compliance effect as standard stringency is increased. Enhanced data quality assurance and data adjustment may be necessary to achieve the improved accuracy required to judge compliance with tighter standards.

Measurement of microenvironmental ozone concentrations in Durham, North Carolina, using a 2B Technologies 205 Federal Equivalent Method monitor and an interference-free 2B Technologies 211 monitor

During August and September of 2012, researchers conducted a microenvironmental (ME) monitoring study in Durham, North Carolina, using two 2B Technologies O3 monitors: a dual-beam model 205 Federal Equivalent Method (FEM) 254 nm photometer and a newly developed model 211 interference-free dual-beam photometer. The two monitors were mounted in a wheeled, fan-cooled suitcase together with a battery, a disposable N2O cartridge for the model 211 monitor, and filtered sample lines. A scripted technician made paired O3 measurements in a variety of MEs within 2 miles of a fixed-site FEM O3 photometer at the Durham National Guard Armory. The ratio of the 211 to Armory O3 concentrations tended to be lowest (<0.3) for 45 indoor MEs and highest (>0.8) for 104 outdoor MEs. The mean values of the ratio for in-vehicle MEs tended to fall between 0.2 and 0.7—the mean for all 27 in-car tests was 0.3. The ratio values for indoor MEs tended to be higher when the enclosure was well ventilated. The outdoor ratios tended to be lower when the measurement was made downwind of nearby roadways, likely due to exhaust NO. The in-vehicle ratios tended to be larger with windows open than closed; the smallest occurred with closed windows, active air conditioning, and vent recirculation. The 205 − 211 measurement differences were generally small, with 94% of the 176 sample differences below 5 ppb. Five differences were above 10 ppb with the largest values (173.9 and 63.6 ppb) occurring inside a violin repair shop. Roadway proximity tended to increase the differences for outdoor locations. The largest in-vehicle difference (6 ppb) occurred at a convenience store service station. As addressed in regulatory models, such differences may reduce estimated population O3 exposure by 30–50% in indoor and in-vehicle MEs where individuals spend more than 80% of their time. Implications: Computer models used to estimate exposures of human populations—such as the Air Pollution Exposure Model (APEX) developed by the U.S. Environmental Protection Agency—can be improved by use of direct microenvironmental (ME) measurement comparisons to nearby fixed-site monitors used for determining regulatory compliance. Simultaneous measurements made by model 211 and model 205 ozone monitors in a variety of MEs indicated that Federal Equivalent Method photometers similar to the model 205 may read high in the presence of various interferences associated with indoor sources and motor vehicles, increasing modeled exposures in such environments by 20–100%.