Comparison of Outdoor and Classroom Ozone Exposures for School Children in Mexico City

Abstract

To evaluate methods of reducing exposure of school children in southwest Mexico City to ambient ozone, outdoor ozone levels were compared to indoor levels under three distinct classroom conditions: windows/doors open, air cleaner off; windows/doors closed, air cleaner off; windows/ doors closed, air cleaner on. Repeated two-minute average measurements of ozone were made within five minutes of each other inside and outside of six different school classrooms while children were in the room. Outdoor ozone two-minute average levels varied between 64 and 361 ppb; mean outdoor levels were above 160 ppb for each of the three conditions. Adjusting for outdoor relative humidity, for a mean outdoor ozone concentration of 170 ppb, the mean predicted indoor ozone concentrations were 125.3 (±5.7) ppb with windows/doors open; 35.4 (±4.6) ppb with windows/ doors closed, air cleaner off; and 28.9 (±4.3) ppb with windows/ doors closed, air cleaner on. The mean predicted ratios of indoor to outdoor ozone concentrations were 0.71 (±0.03) with windows/doors open; 0.18 (±0.02) ppb with windows/doors closed, air cleaner off; and 0.15 (±0.02) ppb with windows/doors closed, air cleaner on. As outdoor ozone concentrations increased, indoor ozone concentrations increased more rapidly with windows and doors open than with windows and doors closed. Ozone exposure in Mexican schools may be significantly reduced, and can usually be kept below the World Health Organization (WHO) guideline of 80 ppb, by closing windows and doors even when ambient ozone levels reach 30Q ppb or more.     

Numerical Evaluation of the Effect of Traffic Pollution on Indoor Air Quality of a Naturally Ventilated Building

Abstract

A computational fluid dynamics technique was used to evaluate the effect of traffic pollution on indoor air quality of a naturally ventilated building for various ventilation control strategies. The transport of street-level nonreactive pollutants emitted from motor vehicles through the indoor environment was simulated using the large eddy simulation (LES) of the turbulent flows and the pollutant transport equations. The numerical model developed herein was verified by available wind-tunnel measurements. Good agreement with the measured velocity and concentration data was found. Twelve sets of numerical scenario simulations for various roof- and side-vent openness and outdoor wind speeds were carried out. The effects of the air change rate, the indoor airflow pattern, and the external pollutant dispersion on indoor air quality were investigated. The control strategies of ventilation rates and paths for reducing incoming vehicle pollutants and maintaining a desirable air change rate are proposed to reduce the impact of outdoor traffic pollution during traffic rush hours. It was concluded that the windward side vent is a significant factor contributing to air change rate and indoor air quality. Air intakes on the leeward side of the building can effectively reduce the peak and average indoor concentration of traffic pollutants, but the corresponding air change rate is relatively low. Using the leeward cross-flow ventilation with the windward roof vent can effectively lower incoming vehicle pollutants and maintain a desirable air change rate during traffic rush hours.     

Numerical evaluation of the effect of traffic pollution on indoor air quality of a naturally ventilated building

A computational fluid dynamics technique was used to evaluate the effect of traffic pollution on indoor air quality of a naturally ventilated building for various ventilation control strategies. The transport of street-level nonreactive pollutants emitted from motor vehicles through the indoor environment was simulated using the large eddy simulation (LES) of the turbulent flows and the pollutant transport equations. The numerical model developed herein was verified by available wind-tunnel measurements. Good agreement with the measured velocity and concentration data was found. Twelve sets of numerical scenario simulations for various roof- and side-vent openness and outdoor wind speeds were carried out. The effects of the air change rate, the indoor airflow pattern, and the external pollutant dispersion on indoor air quality were investigated. The control strategies of ventilation rates and paths for reducing incoming vehicle pollutants and maintaining a desirable air change rate are proposed to reduce the impact of outdoor traffic pollution during traffic rush hours. It was concluded that the windward side vent is a significant factor contributing to air change rate and indoor air quality. Air intakes on the leeward side of the building can effectively reduce the peak and average indoor concentration of traffic pollutants, but the corresponding air change rate is relatively low. Using the leeward cross-flow ventilation with the windward roof vent can effectively lower incoming vehicle pollutants and maintain a desirable air change rate during traffic rush hours.     

On the Relation Between the Indoor and Outdoor Concentrations of Nitrogen Oxides

Simultaneous measurements were made of the concentrations of NO, NO₂, and CO inside and outside of a building. The building is located in the Los Angeles area, which is heavily polluted by photochemical smog, and the experiments were conducted at a time of the year when the pollutants in question tend to be high. The results shows that there is a direct relationship between the inside and outside concentrations, and that the phase lag between the concentrations depends principally on the ratio of the building volume to the ventilation rate. Although the outside concentrations of the pollutants in question did not follow the same pattern every day, peak concentrations seemed to be related to “rush-hour” traffic. By reducing ventilation rates during these periods, it may be possible to reduce the concentration peaks inside of the building. The building involved in the current study was not located in the immediate vicinity of heavy traffic, and the indoor concentrations of NO, NO₂, and CO did not appear to be very severe when compared to those defined by present air quality standards. Finally, the results support the belief that NO and O₃ do not co-exist indoors except in very small quantities.     

Influence of trees on the dispersion of pollutants in an urban street canyon—Experimental investigation of the flow and concentration field

Flow field and concentration measurements have been performed in an idealized model of an urban street canyon with one row of trees arranged along the center axis. The model was set up in an atmospheric boundary layer wind tunnel and the approach flow was directed perpendicular to the street axis. A line source embedded in the bottom of the street was used to release tracer gas for the simulation of traffic exhaust emissions. Trees with spherical crowns were modeled and positioned inside the street canyon, varying crown diameter, crown permeability, trunk height and tree spacing. Traffic-induced turbulence was simulated by rotating belts with thin plates. Concentrations were measured at the facades of the street canyon. For small tree crowns, only little changes in concentration were measured, however, increasing crown diameters led to increasing concentrations at the leeward street canyon wall associated with a reduction of local concentrations at the windward wall. For some cases, a variation of trunk height led to a modification of the concentration pattern on the walls. Increasing the tree spacing resulted in a noticeable concentration decrease. When compared to the situation with standing (but emitting) traffic, the traffic-induced turbulence by two-way car movements always contributed to a more homogenous concentration field inside the street canyon yielding to reduced mean concentration levels.     

Effects of a constructional intervention on airborne and deposited particulate matter in the Portuguese National Tile Museum, Lisbon

In the 1970s, a large ambulatory of the National Tile Museum, Lisbon, was closed with glass panes on both ground and first floor. Although this design was meant to protect the museum collection from ambient air pollutants, small openings between the glass panes remain, creating a semi-enclosed corridor. The effects of the glass panes on the indoor air quality were evaluated in a comparative study by monitoring the airborne particle concentration and the extent of particle deposition at the enclosed corridor as well as inside the museum building. Comparison of the indoor/outdoor ratio of airborne particle concentration demonstrated a high natural ventilation rate in the enclosed corridor as well as inside the museum building. PM₁₀ deposition velocities on vertical surfaces were estimated in the order of 3?×?10^?4 m s^?1 for both indoor locations. Also, the deposition rates of dark-coloured and black particles in specific were very similar at both indoor locations, causing visual degradation. The effectiveness of the glass panes in protecting the museum collection is discussed.     

Modeling of Radon and Its Daughter Concentrations in Ventilated Spaces

In order to predict indoor radiation levels due to radon daughters at low building ventilation and air leakage rates, differential equations governing the decay and venting of radon (Rn-222) and its daughters were used. A computer program based on the equations was written to predict radon and daughter concentrations, total potential alpha energy concentration and equilibrium factor. The program can account for time dependence of ventilation and emanation rates and is readily used by building designers.

Sample calculations using the program showed that potential alpha energy levels in tightened buildings can commonly reach about 0.01 working level (WL), a level more than twice as high as concentrations currently found in most houses.     

Comparison of indoor and outdoor concentrations of CO at a public school. Evaluation of an indoor air quality model

A field study was carried out to investigate the internal and external carbon monoxide (CO) concentration levels of a public school building in Athens, Greece. Simultaneous measurements of indoor and outdoor CO concentrations were conducted using a non-dispersive infrared analyzer. Measurements of mean hourly CO concentrations inside and outside the sampling room were conducted on a 24-h basis for 13 consecutive days during May and June 1999 and for 14 consecutive days during December 1999. The aim of the study was to investigate the attenuation pattern of external pollution levels within the building. The diurnal concentration variations reported for different days during the week show that indoor CO concentrations are in general lower than the respective outdoor levels, and that the morning peaks of indoor concentrations show a delay of 1 h or less compared to the morning peaks of outdoor concentrations. The measured indoor to outdoor concentration ratios show a seasonal variation. An indoor air quality model for the prediction of indoor concentration levels developed by Hayes (J. Air Pollut. Control Assoc. 39 (11) (1989) 1453; J. Air Waste Manage. Assoc. 41 (2) (1991) 161) is coded as a computer program and evaluated using the experimental data. The model results are in good agreement with the indoor concentration measurements, although in some cases the model cannot respond adequately to sharp outdoor concentration changes. The ratio between measured and predicted daily maximum indoor concentration ranges between 0.88 and 1.23. The regression curve between predicted by the model and measured hourly indoor concentrations, for a continuous period of 96 h, has a slope of 0.64 and a coefficient of determination (R²) of 0.69.     

Indoor/Outdoor Ozone Concentrations at a Contemporary Art Gallery

Ozone concentrations were measured both inside and outside the Sainsbury Centre for Visual Arts, near a small city in rural eastern England, during a three-week period in summer. The inside concentration was typically 70 ± 10% of the outside concentration during the period of expected maximum outside levels. During the period of observation the maximum outside ozone levels ranged up to 60 ppb, although there have been periods at this location where outside ozone levels have been well in excess of 120 ppb. The relatively high indoor/outdoor ozone ratio is a function of the Centre’s design, its internal geometry, and its ventilation system. Conventional art galleries and museums experience much lower indoor ozone exposure. The measured indoor ozone levels imply deleterious effects on the gallery exhibits and an enhanced ozone exposure may have to be considered in the design of modern galleries and museums.     

Numerical calculation of flow and stack-gas concentration fluctuation around a cubical building

A numerical simulation model was developed to predict the instantaneous concentration fluctuation of a plume and applied to stack-gas diffusion around a cubical building. The flow field, including an instantaneous velocity component, was predicted using the large eddy simulation (LES) method in the developed numerical model. Then, the instantaneous concentration fluctuation was predicted using the obtained unsteady flow field. Concentration was calculated using the finite difference method, in which the LES is expanded for concentration, and the puff method, in which small volumes of the tracer gas are divided and combined according to the calculation mesh sizes. In order to avoid numerical viscous effects, a puff method and finite difference method were applied separately in the regions near and far from the stack-gas release point, respectively. Then, the flow field around a cubical building and the diffusion of stack-gas, emitted from an elevated point source at an upstream position of the building, were calculated using the model mentioned above. Numerical calculation results were compared with those obtained in wind tunnel experiments in which concentration fluctuation was measured using high-response flame ionization detectors. Although there were some discrepancies in the flow field between the calculated results and those of wind tunnel experiments, e.g., the calculated windward length of a cavity region behind the building, the calculated mean velocity and turbulent intensity showed good agreement with those of the wind tunnel experiments. Furthermore, the calculated concentration fluctuation showed good agreement with that in the wind tunnel, not only regarding the features of fluctuating concentration signals, but also statistic quantities, viz., mean concentration, fluctuation intensity and high-concentration values.     

Effects of Strength and Position of Pollutant Source on Pollutant Dispersion Within an Urban Street Canyon

A two-dimensional numerical model for simulating airflow and pollutant dispersion inside an urban street canyon was first developed using the FLUENT code, and then it was validated against a wind tunnel experiment. Then the effects of strength and position of pollutant sources on pollutant dispersion within an urban street canyon were investigated numerically. The numerical results showed that the dimensionless pollutant concentrations within the urban street canyon were independent from the source strength. The results also revealed that the pollutant distributions inside the urban street canyon with a two-lane road were influenced significantly by the positions of the two sources: 1) the closer the two sources were to the street center of the canyon, the lower the pollutant concentrations on the leeward wall and at the human respiration level in the leeward footpath became; 2) the pollutant concentrations on the windward wall and at the human respiration level in the windward footpath were not sensitive to the locations of the two sources as long as the source on the windward lane was situated outside the small recirculation zone at the bottom corner of the canyon windward wall; 3) the pollutant concentrations on the lower parts of the windward and leeward walls as well as in the two footpaths increased greatly when the two sources were moved from outside into the small recirculation zones.     

Control of volatile organic compounds indoors—Development of an integrated mass-transfer-based model and its application

Building envelopes are usually comprised of several different layers of building materials, which may alternatively act as VOC sources or sinks depending on their emission and sorption potentials and the indoor environmental conditions as well. In this research, a whole room IAQ model consisting of multi-phase emission/sorption model for wall materials and room volume mass balance model catering for practical ventilation schemes was developed. The interactions of VOC and building materials composing different building components can be modeled based on fundamental mass transfer theories. The effects of various construction materials and ventilation strategies on the emission characteristics were investigated. Results show that measures like pre-occupancy flush-out, lead-time ventilation, etc. have substantial impacts on indoor VOC concentration and the model can successfully handle different building scenarios. Although more rigorous validation, in particular more experimental verification, is needed, the proposed model has proven to be valuable in handling different building scenarios. It is useful in analyzing the levels of contaminant buildup that would occur during no ventilation period for intermittent ventilation situations and in determining the amount of outdoor air and the lead-time period required to flush out the contaminants prior to occupancy. It is likely to be a simple routine tool for building owners, designers and operators to attain acceptable indoor VOC concentration level.     

Health Effects and Energy Choices

ABSTRACT

Day- and nighttime total suspended particulate matter was collected inside and outside Emperor Qin's Terra-Cotta Museum in winter and summer 2008. The purpose was to characterize the winter and summer differences of indoor airborne particles in two display halls with different architectural and ventilation conditions, namely the Exhibition Hall and Pit No. 1. The morphology and elemental composition of two season samples were investigated using scanning electron microscopy and energy dispersive X-ray spectrometry. It is found that the particle size, particle mass concentration, and particle type were associated with the visitor numbers in the Exhibition Hall and with the natural ventilation in Pit No. 1 in both winter and summer. Evident winter and summer changes in the composition and physicochemical properties of the indoor suspended particulate matters were related to the source emission and the meteorological conditions. Particle mass concentrations in both halls were higher in winter than in summer. In winter, the size of the most abundant particles at the three sites were all between 0.5 and 1.0 μm, whereas in summer the peaks were all located at less than 0.5 μm. The fraction of sulfur-containing particles was 2–7 times higher in winter than in summer. In addition to the potential soiling hazard, the formation and deposition of sulfur-containing particles in winter may lead to the chemical and physical weathering of the surfaces of the terra-cotta statues.

IMPLICATIONS Relatively few microanalyses of indoor airborne particles inside museums in China have been performed. The mass concentrations of winter and summer indoor total suspended particulate (TSP) are presented for the Emperor Qin's Terra-Cotta Museum along with the characterization of individual particles via computerized scanning electron microscopy and an energy dispersive X-ray spectrometry. The results indicate that both the high level of particle mass concentrations in winter and the predominant fine particles in summer were responsible for the soiling of the statues over a long period of time. The irreplaceable statues were also facing with weathering hazards posed by abundant sulfur-containing particles, especially in winter. Data provided in this study suggested that mechanical ventilation, air filtration, and air conditioning systems should be installed in Pit No. 1 display hall and proper display strategy should be adopted in Exhibition Hall.     

Use of an indoor air quality model (IAQM) to estimate indoor ozone levels

Currently, outdoor ozone levels in many U.S. cities exceed the primary health-based national ambient air quality standard. While outdoor ozone levels are an important measure of the severity of those exceedances, people typically spend more than 80 percent of their time indoors, where ozone levels are lower. Indoor ozone levels range from 10 to 80 percent of outdoor levels, with many people receiving a substantial portion of their ozone exposure while indoors. This paper uses an indoor air quality model (IAQM) to estimate indoor ozone levels by microenvironment type (home, office, and vehicle) and configuration (windows open, windows closed, older construction, weatherized, and air conditioned). The formulation of IAQM is discussed, along with specification of model parameters for ozone. The multicompartment version of IAQM is described, with a single-compartment version used for the analyses. IAQM-calculated ozone indoor-outdoor ratios compare well with research-reported values. Results indicate that ozone peak-concentration indoor-outdoor ratios range as follows: home--0.65 (windows open), 0.36 (air conditioned), 0.23 (typical construction, windows closed), and 0.05 (energy-efficient construction, windows closed); office--0.82 (heating, ventilation and air conditioning systems supplying 100 percent outdoor air), 0.60 (typical HVAC), and 0.32 (energy-efficient HVAC); and vehicle--0.41 (85 mph), 0.33 (55 mph), and 0.21 (10 mph). Analysis results are presented to characterize IAQM's sensitivity to assumed model parameters.     

The effect of different ventilation modes on in-vehicle carbon monoxide exposure

In-vehicle carbon monoxide (CO) concentration profiles were monitored in a passenger vehicle driven along a heavily traveled route of a commercial/residential area of Beirut, Lebanon, under several ventilation modes. Trips were conducted during morning rush hours in spring and summer time. Concomitant monitoring of car-exterior CO level, ambient CO level and wind speed was also undertaken. The highest mean CO exposure was experienced for the “windows closed, vents closed” and “windows closed, AC on recirculation” ventilation settings, with mean CO levels of 37.4 and 30.8 ppm, respectively, exceeding the 1-h air quality guidelines. The exposure was less significant for other ventilation modes with respective mean values of $10.8–19\mathrm{ppm}$. Mean car-exterior CO levels were lower than the 1-h air quality guidelines, but exceeded the 8-h CO exposure guidelines. Ambient CO levels were low and non-representative of the personal exposure of individuals neither inside nor in the vicinity of road vehicles. In-vehicle CO levels revealed moderate to good correlations to out-vehicle CO levels for ventilation modes allowing for outdoor air intake, and no correlation to ambient CO levels and wind speed. Infiltration as a result of indoor–outdoor air exchange and intrusion from engine combustion/exhaust infiltration constituted the main sources of observed in-vehicle CO levels.     

Outdoor/Indoor/Personal ozone exposures of children in Nashville, Tennessee

An ozone (O3) exposure study was conducted in Nashville, TN, using passive O3 samplers to measure six weekly outdoor, indoor, and personal O3 exposure estimates for a group of 10- to 12-yr-old elementary school children. Thirty-six children from two Nashville area communities (Inglewood and Hendersonville) participated in the O3 sampling program, and 99 children provided additional time-activity information by telephone interview. By design, this study coincided with the 1994 Nashville/Middle Tennessee Ozone Study conducted by the Southern Oxidants Study, which provided enhanced continuous ambient O3 monitoring across the Nashville area. Passive sampling estimated weekly average outdoor O3 concentrations from 0.011 to 0.O30 ppm in the urban Inglewood community and from 0.015 to 0.042 ppm in suburban Hendersonville. The maximum 1- and 8-hr ambient concentrations encountered at the Hendersonville continuous monitor exceeded the levels of the 1- and 8-hr metrics for the O3 National Ambient Air Quality Standard. Weekly average personal O3 exposures ranged from 0.0013 to 0.0064 ppm (7-31% of outdoor levels). Personal O3 exposures reflected the proportional amount of time spent in indoor and outdoor environments. Air-conditioned homes displayed very low indoor O3 concentrations, and homes using open windows and fans for ventilation displayed much higher concentrations.     

Characterizing the occurrence, sources, and variability of radon in Pacific Northwest homes

A compilation of data from earlier studies of 172 homes in the Pacific Northwest indicated that approximately 65 percent of the 46 homes tested in the Spokane River Valley/Rathdrum Prairie region of eastern Washington/northern Idaho had heating season indoor radon (222Rn) concentrations above the U. S. EPA guideline of 148 Bq m-3 (4 pCi L-1). A subset of 35 homes was selected for additional study. The primary source of indoor radon in the Spokane River Valley/Rathdrum Prairie was pressure-driven flow of soil gas containing moderate radon concentrations (geometric mean concentration of 16,000 Bq m-3) from the highly permeable soils (geometric mean permeability of 5 x 10(-11) m2) surrounding the house substructures. Estimated soil gas entry rates ranged from 0.4 to 39 m3h-1 and 1 percent to 21 percent of total building air infiltration. Radon from other sources, including domestic water supplies and building materials was negligible. In high radon homes, winter indoor levels averaged 13 times higher than summer concentrations, while in low radon homes winter levels averaged only 2.5 times higher. Short-term variations in indoor radon were observed to be dependent upon indoor-outdoor temperature differences, wind speed, and operation of forced-air furnace fans. Forced-air furnace operation, along with leaky return ducts and plenums, and openings between the substructure and upper floors enhanced mixing of radon-laden substructure air throughout the rest of the building.     

The impact of a building implosion on airborne particulate matter in an urban community

In response to community concerns, the air quality impact of imploding a 22-story building in east Baltimore, MD, was studied. Time- and space-resolved concentrations of indoor and outdoor particulate matter (PM) (nominally 0.5-10 microm) were measured using a portable nephelometer at seven and four locations, respectively. PM10 levels varied in time and space; there was no measurable effect observed upwind of the implosion. The downwind peak PM10 levels varied with distance (54,000-589 microg/m3) exceeding pre-implosion levels for sites 100 and 1130 m 3000- and 20-fold, respectively. Estimated outdoor 24-hr integrated mass concentrations varied from 15 to 72 microg/m3. The implosion did not result in the U.S. Environmental Protection Agency (EPA) National Ambient Air Quality Standard (NAAQS) for PM10 being exceeded. X-ray fluorescence analysis indicated that the elemental composition was dominated by crustal elements: calcium (57%), silicon (23%), aluminum (7.6%), and iron (6.1%). Lead was above background but at a low level (0.17 microg/m3). Peak PM10 concentrations were short-lived; most sites returned to background within 15 min. No increase in indoor PM10 was observed even at the most proximate 250 m location. These results demonstrate that a building implosion can have a severe but short-lived impact on community air quality. Effective protection is offered by being indoors or upwind.     

Impacts of Upstream Building Width and Upwind Building Arrangements on Airflow and Pollutant Dispersion in a Street Canyon

A two-dimensional numerical model for evaluating the wind flow and pollutant dispersion within a street canyon was first developed using the FLUENT code, which was then validated against a wind tunnel experiment. Then, the effects of the upstream building width and upwind building arrangement on the airflow and pollutant dispersion inside an isolated street canyon were investigated numerically. The numerical results revealed that: (1) the in-canyon vortex center shifts downwards as the upstream building width increases; (2) the recirculation zone covers the entire upstream building roof for the cases when W/H = 0.5, 1.0, 1.5, and 2.0 (W is the upstream building width and H is the building height), whereas the flow reattaches the upstream building roof for the cases when W/H = 2.5 and 3.0; (3) when the upstream building width is shorter than the critical width W_C (= 2H), an increase in the upstream building width leads to an increase in the pollution level on the leeward wall of the canyon and a decrease in the roof-level concentrations at the upstream building; (4) when the upstream building width is longer than the critical width, the roof-level concentrations at the upstream building are negligibly small and the pollution level on the leeward wall of the canyon is almost unaffected by a further increase in the upstream building width; (5) when the buildings are placed upwind of the canyon, the flow attaches the upstream building roof and, therefore, almost none of the pollutants are distributed on the upstream building roof; and (6) the pollution levels inside the canyon and on the downstream building roof increase significantly with the number of upwind buildings.