Atmospheric Environment (v.41, #25)
Editorial board (i).
Particles, aerosols, and their transport in the built environment by Qingyan Yan Chen; Xudong Yang; Bin Zhao (5179-5180).
Biodiversity and concentrations of airborne fungi in large US office buildings from the BASE study by Feng C. Tsai; Janet M. Macher; Yun-Yi Hung (5181-5191).
The Building Assessment Survey and Evaluation (BASE) study measured baseline concentrations of airborne fungi in 100 representative US office buildings in 1994–1998. Multiple samples for different sampling durations, sites, and times of the day were aggregated into building-wide indoor and outdoor average concentrations. Fungal concentrations were compared between locations (indoor vs. outdoor), sampling and analytical methods (culture vs. microscopy), and season (summer vs. winter). The arithmetic means (standard deviations) of the indoor/outdoor concentrations of culturable fungi and fungal spores were 100/680 (230/840) CFU m - 3 and 270/6540 (1190/6780) spore m - 3 , respectively. Although fewer groups were observed indoors than outdoors, at lower average concentrations (except in two buildings), site-specific and building-wide indoor measurements had higher coefficients of variation. More groups were seen in summer, and aggregated concentrations tended to be higher than in winter except for culturable Aureobasidium spp. and Botrytis spp. outdoors and non-sporulating fungi in both locations. Rankings of the predominant fungi identified by both methods were similar, but overall indoor and outdoor spore concentrations were approximately 3 and 10 times higher, respectively, than concentrations of culturable fungi. In the 44 buildings with both measurements, the indoor and outdoor total culturable fungi to fungal spore ratios (total C / S ratios) were 1.27 and 0.25, with opposite seasonal patterns. The indoor C / S ratio was higher in summer than in winter (1.47 vs. 0.86; N = 29 and 15, respectively), but the outdoor ratio was lower in summer (0.19 vs. 0.36, respectively). Comparison of the number of different fungal groups and individual occurrence in buildings and samples indicated that the outdoor environment and summer season were more diverse, but the proportional contributions of the groups were very similar suggesting that the indoor and outdoor environments were related as were summer and winter seasons for each location. The extreme (e.g., 90th percentile) indoor concentrations ( 200 CFU m - 3 and 210 spore m - 3 ) may provide reference values for non-complaint US office environments.
Keywords: Baseline concentrations; Bioaerosols; Fungal diversity; Indoor–outdoor relationship; Seasonal variation;
Assessment of indoor air in Austrian apartments with and without visible mold growth by D. Haas; J. Habib; H. Galler; W. Buzina; R. Schlacher; E. Marth; F.F. Reinthaler (5192-5201).
Fungal spores are transported across great distances in the outdoor air and are also regularly found indoors. Building conditions and behavior-related problems in apartments may lead to massive growth of mold within a very short period of time.The aim of this study was to evaluate whether the visible growth of mold indoors influences the concentration of fungal spores in the air as well as the variety of their species. Samples were collected from 66 households in Austria. For each sampling, the corresponding outdoor air was measured as reference value. The size of the visible mold growth was categorized in order to correlate the extent of mold growth with the concentration of airborne spores as well as the fungal genera. In order to determine fungal spore concentrations in the air, the one-stage MAS-100® air sampler was used. Malt extract agar (MEA) and dichloran glycerol agar (DG18) plates were used as culture media. The total colony forming units (CFU) per m3 were determined. The fungi were identified from the isolated colonies.The results show that in apartments visibly affected by mold, the median values were significantly higher than those of apartments without visible mold growth. The extent of visible mold growth is significantly correlated with both concentration of fungal spores (p<0.001) as well as the predominance of Penicillium sp. and Aspergillus sp. (p<0.001) in indoor air. The total fungal concentration of Penicillium and Aspergillus in the air of apartments is recommended for assessing fungal exposure.
Keywords: Airborne fungi; Indoor air; Outdoor air; Mold growth; Apartments; Air sampling;
Further studies of oxidation processes on filter surfaces: Evidence for oxidation products and the influence of time in service by Gabriel Bekö; Geo Clausen; Charles J. Weschler (5202-5212).
The sensory pollutants emitted by loaded ventilation filters are assumed to include products formed via oxidation of organics associated with captured particles. In this study, experiments were performed that used either particle production or ozone removal as probes to further improve our understanding of such processes. The measured ratio of downstream to upstream submicron particle concentrations increased when ozone was added to air passing through samples from loaded particle filters. Such an observation is consistent with low volatility oxidation products desorbing from the filter and subsequently partitioning between the gas phase and the surface of particles that have passed through the filter, including particles that were previously too small (<20 nm) to be detected by the instrument used in these studies. A related set of experiments conducted with unused filters and filters that had been in service from 2 to 16 weeks found that ozone removal efficiencies changed in a manner that indicated at least two different removal mechanisms—reactions with compounds present on the filter media following manufacturing and reactions with compounds associated with captured particles. The contribution from the former varies with the type and manufacturer of the filter, while that of the latter varies with the duration of service and nature of the captured particles. In complimentary experiments, a filter sample protected from ozone during its 9 weeks of service had higher ozone removal efficiencies than an identical filter not protected from ozone during the same 9 weeks of service filtering the same air. This result indicates that a filter's exposure history subsequently influences the quantity of oxidation products generated when ozone-containing air flows through it.
Keywords: Sub-micron particles; Gas/particle partitioning; Oxidation; Ozone; Ventilation filters; Semi-volatile organic compounds;
The impact of building recirculation rates on secondary organic aerosols generated by indoor chemistry by M.S. Zuraimi; C.J. Weschler; K.W. Tham; M.O. Fadeyi (5213-5223).
Numerous investigators have documented increases in the concentrations of airborne particles as a consequence of ozone/terpene reactions in indoor environments. This study examines the effect of building recirculation rates on the concentrations of secondary organic aerosol (SOA) resulting from reactions between indoor limonene and ozone. The experiments were conducted in a large environmental chamber using four recirculation rates (11, 14, 19 and 24 air change per hour (ACH)) and a constant outdoor air exchange rate (1 ACH) as well as constant emission rates for limonene and ozone. As the recirculation rates increased, the deposition velocities of ozone and SOA increased. As a consequence of reduced production rates (due to less ozone) and larger surface removal rates, number and mass concentrations of SOA in different size ranges decreased significantly at higher recirculation rates. Enhanced coagulation at higher recirculation rates also reduced particle number concentrations, while shifting size-distributions towards larger particles. The results have health implications beyond changes in exposures, since particle size is a factor that determines where a particle deposits in the respiratory tract.
Keywords: Recirculation rates; Secondary organic aerosols (SOAs); Ozone-initiated chemistry; Particle size-distributions; Surface removal; Coagulation;
The effects of electric fields on charged molecules and particles in individual microenvironments by K.S. Jamieson; H.M. ApSimon; S.S. Jamieson; J.N.B. Bell; M.G. Yost (5224-5235).
Measurements of small air ion concentrations, electrostatic potential and AC electric field strengths were taken in an office setting to investigate the link between electric fields and charged molecule and particle concentrations in individual microenvironments. The results obtained indicate that the electromagnetic environments individuals can be exposed to whilst indoors can often bear little resemblance to those experienced outdoors in nature, and that many individuals may spend large periods of their time in “Faraday cage”-like conditions exposed to inappropriate levels and types of electric fields that can reduce localised concentrations of biologically essential and microbiocidal small air ions. Such conditions may escalate their risk of infection from airborne contaminants, including microbes, whilst increasing localised surface contamination. The degree of “electro-pollution” that individuals are exposed to was shown to be influenced by the type of microenvironment they occupy, with it being possible for very different types of microenvironment to exist within the same room.It is suggested that adopting suitable electromagnetic hygiene/productivity guidelines that seek to replicate the beneficial effects created by natural environments may greatly mitigate such problems.
Keywords: Air ions; Electric fields; Microbes; Charged ultrafine particles;
Comparison of the Eulerian and Lagrangian methods for predicting particle transport in enclosed spaces by Z. Zhang; Q. Chen (5236-5248).
The computational fluid dynamics (CFD) methods have been widely used in modeling particle transport and distribution in enclosed spaces. Generally, the particle models can be classified as either Eulerian or Lagrangian methods while each has its own pros and cons. This investigation is to compare the two modeling methods with an emphasis on their performance of predicting particle concentration distributions in ventilated spaces. Both the Eulerian and Lagrangian models under examination were performed based on the same airflow field calculated by solving the RANS equations with the k – ε turbulence model. The numerical results obtained with the two methods were compared with the experimental data. The comparison shows that both of the methods can well predict the steady-state particle concentration distribution, while the Lagrangian method was computationally more demanding. The two models were further compared in predicting the transient dispersion of the particles from a coughing passenger in a section of airliner cabin. In the unsteady state condition, the Lagrangian method performed better than the Eulerian method.
Keywords: Particle; Eulerian method; Lagrangian method; CFD; Indoor environment; Airliner cabin;
Comparison of a new Eulerian model with a modified Lagrangian approach for particle distribution and deposition indoors by Alvin C.K. Lai; F.Z. Chen (5249-5256).
Understanding of aerosol dispersion characteristics has many scientific and engineering applications. It is recognized that Eulerian or Lagrangian approach has its own merits and limitations. A new Eulerian model has been developed and it adopts a simplified drift–flux methodology in which external forces can be incorporated straightforwardly. A new near-wall treatment is applied to take into account the anisotropic turbulence for the modified Lagrangian model. In the present work, we present and compare both Eulerian and Lagrangian models to simulate particle dispersion in a small chamber. Results reveal that the standard k–ε Lagrangian model over-predicts particle deposition compared to the present turbulence-corrected Lagrangian approach. Prediction by the Eulerian model agrees well with the modified Lagrangian model.
Keywords: Dispersion; Mixing; Particulate matter; Indoor air quality;
Resuspension of allergen-containing particles under mechanical and aerodynamic disturbances from human walking by C. Gomes; J. Freihaut; W. Bahnfleth (5257-5270).
This study presents and develops a controlled and characterized method to explore the influence of specific occupant activity on the aerosolization of allergen-containing particles. Indoor allergen-related diseases are primarily inhalation sensitized and developed, suggesting an aerobiological pathway of allergen-containing carrier particles from dust reservoir to occupant respiration. But the pathways are not well understood or quantified. The influence of occupant walking on particle aerosolization is simulated by a system in which complex floor disturbances are deconvoluted into aerodynamic and mechanical components. Time resolved particle size distributions are measured for particles resuspended from representative samples of flooring materials and different types of floor disturbances in an environmentally controlled experimental chamber. Results indicate aerodynamic disturbances, relative to mechanical, dominate the particle resuspension behavior. Dust type, dust load and floor type showed marginal influences on a normalized surface loading basis. Humidity effects were not clear since during experiments the floor samples may not have reached moisture partitioning equilibrium with the controlled air humidity. Average resuspension rates ranged from 10−7 to 10−3 min−1, having phenomenological consistency with previous, large room or chamber investigations, suggesting the method can be utilized to develop a database for particle resuspension rates.
Keywords: Particle resuspension; Human activity; Allergens; Bio-aerosols; Asthma;
Fine particle counting with aerodynamic particle focusing and corona charging by Z.C. Tan; A.S. Wexler (5271-5279).
The conceptual design and evaluation of a fine particle sizing and counting instrument are introduced in this paper. A corresponding laboratory prototype was developed by coupling aerodynamic particle focusing with corona charging techniques that could detect particle sizes down to 25 nm in diameter. Comparison between the prototype and a condensation particle counter (CPC) using identical monodisperse particles showed that the measurements agreed well for the particle sizes in the range of 60–300 nm.
Keywords: Fine particle; Particle counting; Aerodynamic focusing; Corona charging;
Predicting personal exposure to airborne carbonyls using residential measurements and time/activity data by Weili Liu; Junfeng (Jim) Zhang; Leo R. Korn; Lin Zhang; Clifford P. Weisel; Barbara Turpin; Maria Morandi; Tom Stock; Steve Colome (5280-5288).
As a part of the Relationships of Indoor, Outdoor, and Personal Air (RIOPA) study, 48 h integrated residential indoor, outdoor, and personal exposure concentrations of 10 carbonyls were simultaneously measured in 234 homes selected from three US cities using the Passive Aldehydes and Ketones Samplers (PAKS). In this paper, we examine the feasibility of using residential indoor concentrations to predict personal exposures to carbonyls. Based on paired t-tests, the means of indoor concentrations were not different from those of personal exposure concentrations for eight out of the 10 measured carbonyls, indicating indoor carbonyls concentrations, in general, well predicted the central tendency of personal exposure concentrations. In a linear regression model, indoor concentrations explained 47%, 55%, and 65% of personal exposure variance for formaldehyde, acetaldehyde, and hexaldehyde, respectively. The predictability of indoor concentrations on cross-individual variability in personal exposure for the other carbonyls was poorer, explaining<20% of variance for acetone, acrolein, crotonaldehyde, and glyoxal. A factor analysis, coupled with multiple linear regression analyses, was also performed to examine the impact of human activities on personal exposure concentrations. It was found that activities related to driving a vehicle and performing yard work had significant impacts on personal exposures to a few carbonyls.
Keywords: Carbonyls; Air toxics; Indoor concentration; Aldehydes; Personal exposure;