Academic Appointments

  • Research Engineer, Civil and Environmental Engineering

Professional Education

  • PhD, Stanford University, Environmental Engineering and Science (2011)

All Publications

  • Using Indoor Positioning and Mobile Sensing for Spatial Exposure and Environmental Characterizations: Pilot Demonstration of PM2.5 Mapping ENVIRONMENTAL SCIENCE & TECHNOLOGY LETTERS Cheng, K., Tseng, C., Hildemann, L. M. 2019; 6 (3): 153–58
  • Effectiveness of air purifier on health outcomes and indoor particles in homes of children with allergic diseases in Fresno, California: A pilot study JOURNAL OF ASTHMA Park, H., Cheng, K., Tetteh, A. O., Hildemann, L. M., Nadeau, K. C. 2017; 54 (4): 341-346


    Epidemiologic studies indicate that indoor air pollution is correlated with morbidity caused by allergic diseases. We evaluated the effectiveness of reducing the levels of indoor fine particulate matter <2.5 micrometer diameter (PM2.5) in Fresno, California using air purifiers on health outcomes in children with asthma and/or allergic rhinitis.The active group (with air purifiers) and the control group consisted of eight houses each. Air purifiers were installed in the living rooms and bedrooms of the subjects in the active group during the entire 12-week study duration. Childhood asthma control test, peak flow rate monitoring, and nasal symptom scores were evaluated at weeks 0, 6, and 12.At 12 weeks, the active group showed a trend toward an improvement of childhood asthma control test scores and mean evening peak flow rates, whereas the control group showed deterioration in the same measures. Total and daytime nasal symptoms scores significantly reduced in the active group (p = 0.001 and p = 0.011, respectively). The average indoor PM2.5 concentrations reduced by 43% (7.42 to 4.28 μg/m(3)) in the active group (p = 0.001).Intervention with air purifiers reduces indoor PM2.5 levels with significant improvements in nasal symptoms in children with allergic rhinitis in Fresno.

    View details for DOI 10.1080/02770903.2016.1218011

    View details for Web of Science ID 000400169700002

  • Personal exposure to airborne particulate matter due to residential dryer lint cleaning BUILDING AND ENVIRONMENT Cheng, K., Zheng, D., Tetteh, A. O., Park, H., Nadeau, K. C., Hildemann, L. M. 2016; 98: 145-149
  • Measuring Indoor Air Quality and Engaging California Indian Stakeholders at the Win-River Resort and Casino: Collaborative Smoke-Free Policy Development. International journal of environmental research and public health Klepeis, N. E., Dhaliwal, N., Hayward, G., Acevedo-Bolton, V., Ott, W. R., Read, N., Layton, S., Jiang, R., Cheng, K., Hildemann, L. M., Repace, J. L., Taylor, S., Ong, S., Buchting, F. O., Lee, J. P., Moore, R. S. 2016; 13 (1)


    Most casinos owned by sovereign American Indian nations allow smoking, even in U.S. states such as California where state laws restrict workplace smoking. Collaborations between casinos and public health workers are needed to promote smoke-free policies that protect workers and patrons from secondhand tobacco smoke (SHS) exposure and risks. Over seven years, a coalition of public health professionals provided technical assistance to the Redding Rancheria tribe in Redding, California in establishing a smoke-free policy at the Win-River Resort and Casino. The coalition provided information to the casino general manager that included site-specific measurement of employee and visitor PM2.5 personal exposure, area concentrations of airborne nicotine and PM2.5, visitor urinary cotinine, and patron and staff opinions (surveys, focus groups, and a Town Hall meeting). The manager communicated results to tribal membership, including evidence of high SHS exposures and support for a smoke-free policy. Subsequently, in concert with hotel expansion, the Redding Rancheria Tribal Council voted to accept a 100% restriction of smoking inside the casino, whereupon PM2.5 exposure in main smoking areas dropped by 98%. A 70% partial-smoke-free policy was instituted ~1 year later in the face of revenue loss. The success of the collaboration in promoting a smoke-free policy, and the key element of air quality feedback, which appeared to be a central driver, may provide a model for similar efforts.

    View details for DOI 10.3390/ijerph13010143

    View details for PubMedID 26805860

    View details for PubMedCentralID PMC4730534

  • Mixing and sink effects of air purifiers on indoor PM2.5 concentrations: A pilot study of eight residential homes in Fresno, California AEROSOL SCIENCE AND TECHNOLOGY Cheng, K., Park, H., Tetteh, A. O., Zheng, D., Ouellette, N. T., Nadeau, K. C., Hildemann, L. M. 2016; 50 (8): 835-845
  • Effectiveness of air purifier on health outcomes and indoor particles in homes of children with allergic diseases in Fresno: a pilot study Journal of Asthma Park, H., Cheng, K., Tetteh, A. O., Hildemann, L. M., Nadeau, K. C. 2016
  • Mixing and sink effects of air purifiers on indoor PM2.5 concentrations: A pilot study of eight residential homes in Fresno, California Aerosol Science and Technology Cheng, K., Park, H., Tetteh, A. O., Zheng, D., Ouellette, N. T., Nadeau, K. C., Hildemann, L. M. 2016; 50: 835-845
  • Determining PM2.5 calibration curves for a low-cost particle monitor: common indoor residential aerosols ENVIRONMENTAL SCIENCE-PROCESSES & IMPACTS Dacunto, P. J., Klepeis, N. E., Cheng, K., Acevedo-Bolton, V., Jiang, R., Repace, J. L., Otta, W. R., Hildemann, L. M. 2015; 17 (11): 1959-1966


    Real-time particle monitors are essential for accurately estimating exposure to fine particles indoors. However, many such monitors tend to be prohibitively expensive for some applications, such as a tenant or homeowner curious about the quality of the air in their home. A lower cost version (the Dylos Air Quality Monitor) has recently been introduced, but it requires appropriate calibration to reflect the mass concentration units required for exposure assessment. We conducted a total of 64 experiments with a suite of instruments including a Dylos DC1100, another real-time laser photometer (TSI SidePak™ Model AM-510 Personal Aerosol Monitor), and a gravimetric sampling apparatus to estimate Dylos calibration factors for emissions from 17 different common indoor sources including cigarettes, incense, fried bacon, chicken, and hamburger. Comparison of minute-by-minute data from the Dylos with the gravimetrically calibrated SidePak yielded relationships that enable the conversion of the raw Dylos particle counts less than 2.5 μm (in #/0.01 ft(3)) to estimated PM2.5 mass concentration (e.g. μg m(-3)). The relationship between the exponentially-decaying Dylos particle counts and PM2.5 mass concentration can be described by a theoretically-derived power law with source-specific empirical parameters. A linear relationship (calibration factor) is applicable to fresh or quickly decaying emissions (i.e., before the aerosol has aged and differential decay rates introduce curvature into the relationship). The empirical parameters for the power-law relationships vary greatly both between and within source types, although linear factors appear to have lower uncertainty. The Dylos Air Quality Monitor is likely most useful for providing instantaneous feedback and context on mass particle levels in home and work situations for field-survey or personal awareness applications.

    View details for DOI 10.1039/c5em00365b

    View details for Web of Science ID 000364146800010

    View details for PubMedID 26487426

  • Stochastic modeling of short-term exposure close to an air pollution source in a naturally ventilated room: An autocorrelated random walk method JOURNAL OF EXPOSURE SCIENCE AND ENVIRONMENTAL EPIDEMIOLOGY Cheng, K., Acevedo-Bolton, V., Jiang, R., Klepeis, N. E., Ott, W. R., Kitanidis, P. K., Hildemann, L. M. 2014; 24 (3): 311-318


    For an actively emitting source such as cooking or smoking, indoor measurements have shown a strong "proximity effect" within 1 m. The significant increase in both the magnitude and variation of concentration near a source is attributable to transient high peaks that occur sporadically-and these "microplumes" cause great uncertainty in estimating personal exposure. Recent field studies in naturally ventilated rooms show that close-proximity concentrations are approximately lognormally distributed. We use the autocorrelated random walk method to represent the time-varying directionality of indoor emissions, thereby predicting the time series and frequency distributions of concentrations close to an actively emitting point source. The predicted 5-min concentrations show good agreement with measurements from a point source of CO in a naturally ventilated house-the measured and predicted frequency distributions at 0.5- and 1-m distances are similar and approximately lognormal over a concentration range spanning three orders of magnitude. By including the transient peak concentrations, this random airflow modeling method offers a way to more accurately assess acute exposure levels for cases where well-defined airflow patterns in an indoor space are not available.

    View details for DOI 10.1038/jes.2013.63

    View details for Web of Science ID 000334571000011

    View details for PubMedID 24064529

  • Controlled experiments measuring personal exposure to PM2.5 in close proximity to cigarette smoking. Indoor air Acevedo-Bolton, V., Ott, W. R., Cheng, K., Jiang, R., Klepeis, N. E., Hildemann, L. M. 2014; 24 (2): 199-212


    Few measurements of exposure to secondhand smoke (SHS) in close proximity to a smoker are available. Recent health studies have demonstrated an association between acute (< 2 h) exposures to high concentrations of SHS and increased risk for cardiovascular and respiratory disease. We performed 15 experiments inside naturally-ventilated homes and 16 in outdoor locations, each with 2-4 nonsmokers sitting near a cigarette smoker. The smoker's and nonsmokers' real-time exposures to PM2.5 from SHS were measured by using TSI SidePak monitors to sample their breathing zones. In 87% of the residential indoor experiments, the smoker received the highest average exposure to SHS, with PM2.5 concentrations ranging from 50-630 μg/m(3) . During the active smoking period, individual nonsmokers sitting within ~1 m of a smoker had average SHS exposures ranging from negligible up to >160 μg/m(3) of PM2.5 . The average incremental exposure of the nonsmokers was higher indoors (42 μg/m(3) , n = 35) than outdoors (29 μg/m(3) , n = 47), but the overall indoor and outdoor frequency distributions were similar. The 10-s PM2.5 averages during the smoking periods showed great variability, with multiple high concentrations of short duration (microplumes) both indoors and outdoors. This article is protected by copyright. All rights reserved.

    View details for DOI 10.1111/ina.12057

    View details for PubMedID 23808850

  • Identifying and quantifying secondhand smoke in source and receptor rooms: logistic regression and chemical mass balance approaches. Indoor air Dacunto, P. J., Cheng, K., Acevedo-Bolton, V., Jiang, R., Klepeis, N. E., Repace, J. L., Ott, W. R., Hildemann, L. M. 2014; 24 (1): 59-70


    Identifying and quantifying secondhand tobacco smoke (SHS) that drifts between multiunit homes is critical to assessing exposure. Twenty-three different gaseous and particulate measurements were taken during controlled emissions from smoked cigarettes and six other common indoor source types in 60 single-room and 13 two-room experiments. We used measurements from the 60 single-room experiments for (i) the fitting of logistic regression models to predict the likelihood of SHS and (ii) the creation of source profiles for chemical mass balance (CMB) analysis to estimate source apportionment. We then applied these regression models and source profiles to the independent data set of 13 two-room experiments. Several logistic regression models correctly predicted the presence of cigarette smoke more than 80% of the time in both source and receptor rooms, with one model correct in 100% of applicable cases. CMB analysis of the source room provided significant PM2.5 concentration estimates of all true sources in 9 of 13 experiments and was half-correct (i.e., included an erroneous source or missed a true source) in the remaining four. In the receptor room, CMB provided significant estimates of all true sources in 9 of 13 experiments and was half-correct in another two.

    View details for DOI 10.1111/ina.12049

    View details for PubMedID 23631597

  • Outdoor fine and ultrafine particle measurements at six bus stops with smoking on two California arterial highways-Results of a pilot study JOURNAL OF THE AIR & WASTE MANAGEMENT ASSOCIATION Ott, W. R., Acevedo-Bolton, V., Cheng, K., Jiang, R., Klepeis, N. E., Hildemann, L. M. 2014; 64 (1): 47-60


    As indoor smoking bans have become widely adopted, some U.S. communities are considering restricting smoking outdoors, creating a need for measurements of air pollution near smokers outdoors. Personal exposure experiments were conducted with four to five participants at six sidewalk bus stops located 1.5-3.3 m from the curb of two heavily traveled California arterial highways with 3300-5100 vehicles per hour. At each bus stop, a smoker in the group smoked a cigarette. Gravimetrically calibrated continuous monitors were used to measure fine particle concentrations (aerodynamic diameter < or = 2.5 microm; PM2.5) in the breathing zones (within 0.2 m from the nose and mouth) of each participant. At each bus stop, ultrafine particles (UFP), wind speed, temperature, relative humidity, and traffic counts were also measured. For 13 cigarette experiments, the mean PM2.5 personal exposure of the nonsmoker seated 0.5 m from the smoker during a 5-min cigarette ranged from 15 to 153 microg/m3. Of four persons seated on the bench, the smoker received the highest PM2.5 breathing-zone exposure of 192 microg/m3. There was a strong proximity effect: nonsmokers at distances 0.5, 1.0, and 1.5 m from the smoker received mean PM2.5 personal exposures of 59, 40, and 28 microg/m3, respectively, compared with a background level of 1.7 microg/m3. Like the PM2.5 concentrations, UFP concentrations measured 0.5 m from the smoker increased abruptly when a cigarette started and decreased when the cigarette ended, averaging 44,500 particles/cm3 compared with the background level of 7200 particles/cm3. During nonsmoking periods, the UFP background concentrations showed occasional peaks due to traffic, whereas PM2.5 background concentrations were extremely low. The results indicate that a single cigarette smoked outdoors at a bus stop can cause PM2.5 and UFP concentrations near the smoker that are 16-35 and 6.2 times, respectively, higher than the background concentrations due to cars and trucks on an adjacent arterial highway.Rules banning smoking indoors have been widely adopted in the United States and in many countries. Some communities are considering smoking bans that would apply to outdoor locations. Although many measurements are available of pollutant concentrations from secondhand smoke at indoor locations, few measurements are available of exposure to secondhand smoke outdoors. This study provides new data on exposure to fine and ultrafine particles from secondhand smoke near a smoker outdoors. The levels are compared with the exposure measured next to a highway. The findings are important for policies that might be developed for reducing exposure to secondhand smoke outdoors.

    View details for DOI 10.1080/10962247.2013.832712

    View details for Web of Science ID 000328535100006

  • Identifying and quantifying secondhand smoke in multiunit homes with tobacco smoke odor complaints ATMOSPHERIC ENVIRONMENT Dacunto, P. J., Cheng, K., Acevedo-Bolton, V., Klepeis, N. E., Repace, J. L., Ott, W. R., Hildemann, L. M. 2013; 71: 399-407
  • Real-time particle monitor calibration factors and PM2.5 emission factors for multiple indoor sources ENVIRONMENTAL SCIENCE-PROCESSES & IMPACTS Dacunto, P. J., Cheng, K., Acevedo-Bolton, V., Jiang, R., Klepeis, N. E., Repace, J. L., Ott, W. R., Hildemann, L. M. 2013; 15 (8): 1511-1519


    Indoor sources can greatly contribute to personal exposure to particulate matter less than 2.5 μm in diameter (PM2.5). To accurately assess PM2.5 mass emission factors and concentrations, real-time particle monitors must be calibrated for individual sources. Sixty-six experiments were conducted with a common, real-time laser photometer (TSI SidePak™ Model AM510 Personal Aerosol Monitor) and a filter-based PM2.5 gravimetric sampler to quantify the monitor calibration factors (CFs), and to estimate emission factors for common indoor sources including cigarettes, incense, cooking, candles, and fireplaces. Calibration factors for these indoor sources were all significantly less than the factory-set CF of 1.0, ranging from 0.32 (cigarette smoke) to 0.70 (hamburger). Stick incense had a CF of 0.35, while fireplace emissions ranged from 0.44-0.47. Cooking source CFs ranged from 0.41 (fried bacon) to 0.65-0.70 (fried pork chops, salmon, and hamburger). The CFs of combined sources (e.g., cooking and cigarette emissions mixed) were linear combinations of the CFs of the component sources. The highest PM2.5 emission factors per time period were from burned foods and fireplaces (15-16 mg min(-1)), and the lowest from cooking foods such as pizza and ground beef (0.1-0.2 mg min(-1)).

    View details for DOI 10.1039/c3em00209h

    View details for Web of Science ID 000322177300004

    View details for PubMedID 23784066

  • Measurement of the proximity effect for indoor air pollutant sources in two homes JOURNAL OF ENVIRONMENTAL MONITORING Acevedo-Bolton, V., Cheng, K., Jiang, R., Ott, W. R., Klepeis, N. E., Hildemann, L. M. 2012; 14 (1): 94-104


    Personal exposure to air pollutants can be substantially higher in close proximity to an active source due to non-instantaneous mixing of emissions. The research presented in this paper quantifies this proximity effect for a non-buoyant source in 2 naturally ventilated homes in Northern California (CA), assessing its spatial and temporal variation and the influence of factors such as ventilation rate on its magnitude. To quantify how proximity to residential sources of indoor air pollutants affects human exposure, we performed 16 separate monitoring experiments in the living rooms of two detached single-family homes. CO (as a tracer gas) was released from a point source in the center of the room at a controlled emission rate for 5-12 h per experiment, while an array of 30-37 real-time monitors simultaneously measured CO concentrations with 15 s time resolution at radial distances ranging from 0.25-5 m under a range of ventilation conditions. Concentrations measured in close proximity (within 1 m) to the source were highly variable, with 5 min averages that typically varied by >100-fold. This variability was due to short-duration (<1 min) pollutant concentration peaks ("microplumes") that were frequently recorded in close proximity to the source. We decomposed the random microplume component from the total concentrations by subtracting predicted concentrations that assumed uniform, instantaneous mixing within the room and found that these microplumes can be modeled using a 3-parameter lognormal distribution. Average concentrations measured within 0.25 m of the source were 6-20 times as high as the predicted well-mixed concentrations.

    View details for DOI 10.1039/c1em10521c

    View details for Web of Science ID 000298855800012

    View details for PubMedID 22068152

  • Determination of response of real-time SidePak AM510 monitor to secondhand smoke, other common indoor aerosols, and outdoor aerosol JOURNAL OF ENVIRONMENTAL MONITORING Jiang, R., Acevedo-Bolton, V., Cheng, K., Klepeis, N. E., Ott, W. R., Hildemann, L. M. 2011; 13 (6): 1695-1702


    The amount of light scattered by airborne particles inside an aerosol photometer will vary not only with the mass concentration, but also with particle properties such as size, shape, and composition. This study conducted controlled experiments to compare the measurements of a real-time photometer, the SidePak AM510 monitor (SidePak), with gravimetric mass. PM sources tested were outdoor aerosols, and four indoor combustion sources: cigarettes, incense, wood chips, and toasting bread. The calibration factor for rescaling the SidePak measurements to agree with gravimetric mass was similar for the cigarette and incense sources, but different for burning wood chips and toasting bread. The calibration factors for ambient urban aerosols differed substantially from day to day, due to variations in the sources and composition of outdoor PM. A field evaluation inside a casino with active smokers yielded calibration factors consistent with those obtained in the controlled experiments with cigarette smoke.

    View details for DOI 10.1039/c0em00732c

    View details for Web of Science ID 000291403300019

    View details for PubMedID 21589975

  • Modeling Exposure Close to Air Pollution Sources in Naturally Ventilated Residences: Association of Turbulent Diffusion Coefficient with Air Change Rate ENVIRONMENTAL SCIENCE & TECHNOLOGY Cheng, K., Acevedo-Bolton, V., Jiang, R., Klepeis, N. E., Ott, W. R., Fringer, O. B., Hildemann, L. M. 2011; 45 (9): 4016-4022


    For modeling exposure close to an indoor air pollution source, an isotropic turbulent diffusion coefficient is used to represent the average spread of emissions. However, its magnitude indoors has been difficult to assess experimentally due to limitations in the number of monitors available. We used 30-37 real-time monitors to simultaneously measure CO at different angles and distances from a continuous indoor point source. For 11 experiments involving two houses, with natural ventilation conditions ranging from <0.2 to >5 air changes per h, an eddy diffusion model was used to estimate the turbulent diffusion coefficients, which ranged from 0.001 to 0.013 m² s⁻¹. The model reproduced observed concentrations with reasonable accuracy over radial distances of 0.25-5.0 m. The air change rate, as measured using a SF₆ tracer gas release, showed a significant positive linear correlation with the air mixing rate, defined as the turbulent diffusion coefficient divided by a squared length scale representing the room size. The ability to estimate the indoor turbulent diffusion coefficient using two readily measurable parameters (air change rate and room dimensions) is useful for accurately modeling exposures in close proximity to an indoor pollution source.

    View details for DOI 10.1021/es103080p

    View details for Web of Science ID 000289819400033

    View details for PubMedID 21456572

  • Fine particle air pollution and secondhand smoke exposures and risks inside 66 US casinos ENVIRONMENTAL RESEARCH Repace, J. L., Jiang, R., Acevedo-Bolton, V., Cheng, K., Klepeis, N. E., Ott, W. R., Hildemann, L. M. 2011; 111 (4): 473-484


    Smoking bans often exempt casinos, exposing occupants to fine particles (PM(2.5)) from secondhand smoke. We quantified the relative contributions to PM(2.5) from both secondhand smoke and infiltrating outdoor sources in US casinos. We measured real-time PM(2.5), particulate polycyclic aromatic hydrocarbons (PPAH), and carbon dioxide (CO(2)) (as an index of ventilation rate) inside and outside 8 casinos in Reno, Nevada. We combined these data with data from previous studies, yielding a total of 66 US casinos with smoking in California, Delaware, Nevada, New Jersey, and Pennsylvania, developing PM(2.5) frequency distributions, with 3 nonsmoking casinos for comparison. Geometric means for PM(2.5) were 53.8 μg/m(3) (range 18.5-205 μg/m(3)) inside smoking casinos, 4.3 μg/m(3) (range 0.26-29.7 μg/m(3)) outside those casinos, and 3.1 μg/m(3) (range 0.6-9 μg/m(3)) inside 3 nonsmoking casinos. In a subset of 21 Reno and Las Vegas smoking casinos, PM(2.5) in gaming areas averaged 45.2 μg/m(3) (95% CI, 37.7-52.7 μg/m(3)); adjacent nonsmoking casino restaurants averaged 27.2 μg/m(3) (95% CI, 17.5-36.9 μg/m(3)), while PM(2.5) outside the casinos averaged 3.9 μg/m(3) (95% CI, 2.5-5.3 μg/m(3)). For a subset of 10 Nevada and Pennsylvania smoking casinos, incremental (indoor-outdoor) PM(2.5) was correlated with incremental PPAH (R(2)=0.79), with ventilation rate-adjusted smoker density (R(2)=0.73), and with smoker density (R(2)=0.60), but not with ventilation rates (R(2)=0.15). PPAH levels in 8 smoking casinos in 3 states averaged 4 times outdoors. The nonsmoking casinos' PM(2.5) (n=3) did not differ from outdoor levels, nor did their PPAH (n=2). Incremental PM(2.5) from secondhand smoke in approximately half the smoking casinos exceeded a level known to produce cardiovascular morbidity in nonsmokers after less than 2h of exposure, posing acute health risks to patrons and workers. Casino ventilation and air cleaning practices failed to control secondhand smoke PM(2.5). Drifting PM(2.5) from secondhand smoke contaminated unseparated nonsmoking areas. Smoke-free casinos reduced PM(2.5) to the same low levels found outdoors.

    View details for DOI 10.1016/j.envres.2011.02.007

    View details for Web of Science ID 000290141600001

    View details for PubMedID 21440253

  • Measurement of fine particles and smoking activity in a statewide survey of 36 California Indian casinos JOURNAL OF EXPOSURE SCIENCE AND ENVIRONMENTAL EPIDEMIOLOGY Jiang, R., Cheng, K., Acevedo-Bolton, V., Klepeis, N. E., Repace, J. L., Ott, W. R., Hildemann, L. M. 2011; 21 (1): 31-41


    Despite California's 1994 statewide smoking ban, exposure to secondhand smoke (SHS) continues in California's Indian casinos. Few data are available on exposure to airborne fine particles (PM₂.₅) in casinos, especially on a statewide basis. We sought to measure PM₂.₅ concentrations in Indian casinos widely distributed across California, exploring differences due to casino size, separation of smoking and non-smoking areas, and area smoker density. A selection of 36 out of the 58 Indian casinos throughout California were each visited for 1-3 h on weekend or holiday evenings, using two or more concealed monitors to measure PM₂.₅ concentrations every 10 s. For each casino, the physical dimensions and the number of patrons and smokers were estimated. As a preliminary assessment of representativeness, we also measured eight casinos in Reno, NV. The average PM₂.₅ concentration for the smoking slot machine areas (63 μg/m³) was nine times as high as outdoors (7 μg/m³), whereas casino non-smoking restaurants (29 μg/m³) were four times as high. Levels in non-smoking slot machine areas varied: complete physical separation reduced concentrations almost to outdoor levels, but two other separation types had mean levels that were 13 and 29 μg/m³, respectively, higher than outdoors. Elevated PM₂.₅ concentrations in casinos can be attributed primarily to SHS. Average PM₂.₅ concentrations during 0.5-1 h visits to smoking areas exceeded 35 μg/m³ for 90% of the casino visits.

    View details for DOI 10.1038/jes.2009.75

    View details for Web of Science ID 000285452900006

    View details for PubMedID 20160761

    View details for PubMedCentralID PMC3007589

  • Association of size-resolved airborne particles with foot traffic inside a carpeted hallway ATMOSPHERIC ENVIRONMENT Cheng, K., Goebes, M. D., Hildemann, L. M. 2010; 44 (16): 2062-2066
  • Model-based reconstruction of the time response of electrochemical air pollutant monitors to rapidly varying concentrations JOURNAL OF ENVIRONMENTAL MONITORING Cheng, K., Acevedo-Bolton, V., Jiang, R., Klepeis, N. E., Ott, W. R., Hildemann, L. M. 2010; 12 (4): 846-853


    Electrochemical sensors are commonly used to measure concentrations of gaseous air pollutants in real time, especially for personal exposure investigations. The monitors are small, portable, and have suitable response times for estimating time-averaged concentrations. However, for transient exposures to air pollutants lasting only seconds to minutes, a non-instantaneous time response can cause measured values to diverge from actual input concentrations, especially when the pollutant fluctuations are pronounced and rapid. Using 38 Langan carbon monoxide (CO) monitors, which can be set to log data every 2 s, we found electrochemical sensor response times of 30-50 s. We derived a simple model based on Fick's Law to reconstruct a close to accurate time series from logged data. Starting with experimentally measured data for repetitive step input signals of alternating high and low CO concentrations, we were able to reconstruct a much improved 2-s concentration time series using the model. We also utilized the model to examine errors in monitor measurements for different averaging times. By selecting the averaging time based on the response time of the monitor, the error between actual and measured pollutant levels can be minimized. The methodology presented in this study is useful when aiming to accurately determine a time series of rapidly time-varying concentrations, such as for locations close to an active point source or near moving traffic.

    View details for DOI 10.1039/b921806h

    View details for Web of Science ID 000276532100007

    View details for PubMedID 20383365

  • Near-infrared spectroscopy for in situ monitoring of geoenvironment JOURNAL OF GEOTECHNICAL AND GEOENVIRONMENTAL ENGINEERING Ghandehari, M., Kostarelos, K., Cheng, K., Vimer, C., Yoon, S. 2008; 134 (4): 487-496
  • Simultaneous sampling of gas- and aerosol-phase TDI with a triple filter system JOURNAL OF THE AIR & WASTE MANAGEMENT ASSOCIATION Tsai, C. J., Cheng, K. C., Aggarwal, S. G., Shih, T. S., Hung, I. F. 2003; 53 (10): 1265-1272


    A new triple filter system sampler/model is proposed for the precise and accurate simultaneous sampling and determination of gas- and aerosol-phase 2,4-toluene diisocyanate (TDI). The system consists of two front Teflon filters for sampling aerosol-phase TDI and a final coated glass fiber filter to collect gas-phase TDI. The aerosol-phase TDI is collected on the first Teflon filter, while the second Teflon filter is used to estimate gaseous TDI adsorbed by the first. According to the gas adsorption test of two Teflon filters in series, the TDI gas adsorption fraction of the two filters is almost the same. Results of the evaporation test using pure TDI aerosols collected on the Teflon filter show that significant evaporation of the compound does not occur during sampling. These two findings allow the use of a model to estimate accurate gas- and aerosol-phase TDI concentrations. The comparison test with an annular denuder shows that the triple filter system can minimize the TDI sampling bias between the dual filter and the annular denuder systems.

    View details for Web of Science ID 000185765500013

    View details for PubMedID 14604337