The effects of meteorological factors on atmospheric bioaerosol concentrations--a review.

a time as one year after leaving the Rehabilitation Unit, and about one quarter were not in competitive jobs but were in sheltered employment. Only just over one quarter were still working in ordinary jobs. Their average wage was £8 I is. 6d. Furthermore if one compares the type of work these patients were able to perform there was a definite decline from their premorbid position. The social class grouping before and after rehabilitation was Class II, i-i, Class III, 9-3, Class IV, 4-6, and Class V, IO-I4. Indeed the authors report that 'even the least handicapped of these patients presented continuous problems . . .' and it is noted that such a programme requires special personnel and a great deal of work. Comparing these results with the extra cost in personnel, time, and effort (which could be directed elsewhere) a Doctor Beeching of the psychiatric services would probably scrap such a rehabilitation service before it even started. But is this the right way of looking at it? The authors point out that such a programme, if applied throughout the country, would affect about 6,ooo patients. If the failure rate were the same as in this experiment, about I,500 would be rescued from a disabled life in a mental hospital and once more returned to an at least partially useful and, one assumes, more satisfying life. Obviously more is involved here than mere economics. We were interested to read that as regards behaviour at the Rehabilitation Centre and during the follow-up year 'There were no outstanding differences' between the schizophrenic and the non-schizophrenic rehabilitees. It appears that the group of schizophrenics had difficulties in social adjustment which were even greater than those of work adjustment. '. . . the men concerned had greater difficulty in living outside hospital, than in working outside hospital. If, however, adequate arrangements are made to cater for these various needs, there seems to be every reason to expect that a small selected group of long stay schizophrenic patients can be successfully resettled in work.' The experiment and the report show the high standards we have come so confidently to expect from Dr. Wing and his colleagues, and the publication will be read with interest, not only by psychiatrists, but by all those concemed with rehabilitation problems of chronically disabled patients. J. HOENIG

https://oem.bmj.com/content/oemed/23/2/161.2.full.pdf

The Mechanics of Aerosols

 Bacteria are ubiquitous in the atmosphere, with concentrations of bacterial cells typically exceeding 1×104 m−3 over land Numerous studies have suggested that the presence of bacteria in the atmosphere may impact cloud development, atmospheric chemistry, and microbial biogeography A sound knowledge of bacterial concentrations and distributions in the atmosphere is needed to evaluate these claims This review focusses on published measurements of total and culturable bacteria concentrations in the atmospheric aerosol We discuss emission mechanisms and the impacts of meteorological conditions and measurement techniques on measured bacteria concentrations Based on the literature reviewed, we suggest representative values and ranges for the mean concentration in the near-surface air of nine natural ecosystems and three human-influenced land types We discuss the gaps in current knowledge of bacterial concentrations in air, including the lack of reliable, long-term measurements of the total microbial concentrations in many regions and the scarcity of emission flux measurements

/pdf/bacteria-in-the-global-atmosphere-part-1-review-and-2japsgbxzp.pdf

Bacteria in the global atmosphere – Part 1: Review and synthesis of literature data for different ecosystems

To determine the risks of microbial air pollution from microorganisms used for pesticides and bioremediation, or emanating from composting, fermentation tanks, or other agricultural and urban sources, airborne microbial levels must be evaluated. This study surveyed the atmospheric load of culturable bacteria at four locations in Oregon: a city street, a rye grass field, a Douglas fir forest, and a bluff on the Pacific coast. Samples (20–60 min each) were taken using slit and six-stage cascade samplers. Samples were taken over two 10- or 24-h periods, depending on the site. Meteorological measurements were made at each location. The quantity and type of bacteria found varied by location and time. The highest average number of bacteria during daylight hours was exhibited at the urban site (609 cfu/m3), followed by the forest site (522 cfu/m3), then the rural site (242 cfu/m3), with the lowest concentration found at the coastal site (103 cfu/m3). During the 24-h sampling periods at the rural site, bacterial concentration, in general, tended to increase at sunrise, decrease during the solar noon hours, gradually increase until sunset, then decrease into the evening, with the lowest concentrations occurring between 2100 and 0500 hours. Pigmented bacteria represented between 21 and 62% of the total bacteria sampled; the highest percentage of pigmented bacteria was found at the rural site, and the lowest percentage at the forest site. Bacillus was found to be the most abundant single genus represented at all locations (12–45%). The majority of bacteria found were associated with particles greater than 3 μm aerodynamic diameter. Information gathered from this survey combined with data from the literature and future surveys will contribute to the detection and description of microbial air pollution.

Survey of Culturable Airborne Bacteria at Four Diverse Locations in Oregon: Urban, Rural, Forest, and Coastal

The ecology of bacteria in the alfresco atmosphere

A bioaerosol research chamber was constructed and used to evaluate wind-gust release of previously depositedPseudomonas syringae, spores ofBacillus subtilis var.niger, and fluorescent microspheres (FM) on oat plants, and the airborne survival of the releasedP. syringae. Observations of wind gusts on the releasedBacillus spores and FM showed they had similar particle size distributions and therefore FM could act as bacterial sized surrogates in particle dispersion. Microscopic examination of the released FM containing particles revealed that 84% were associated with either fungal spores and hyphae were epiphytic on the plant, or with plant and soil debris. The release rate ofBacillus spores decreased as the number of gusts experienced by the plants increased, with a greater proportion of larger particles removed. The larger the particle associated with the releasedP. syringae, the longer the bacteria survived.

Artificial wind-gust liberation of microbial bioaerosols previously deposited on plants

Simulated droplet trajectories ofa polydispersed microbial aerosol ina laminar airflowregimen were compared withobserved dispersal patterns ofaerosolized Bacillus subtilis subsp. niger sporesinquasilaminar airflow. Simulated dispersal patterns couldbeexplained intermsofinitial droplet sizes andwhether the droplets evaporated toresidual aeroplanktonic size before settling totheground. Fordroplets thatevaporated jtior tosettling out, avertical downwind size fractionation ispredicted inwhichthemicrobial residue ofthe smallest droplets settles theleast, andisfoundintheairstream atabout sprayerheight, andprogressively larger droplet residues settle toprogressively lower heights. Observations ofsporeparticle size distributions downwind froma spraysourcesupport thesimulation. Droplet andparticle size distributions nearthesource hadthree size fractions: onecontaining large, presumably nonevaporated droplets of.7,umindiameter, and twosmaller fractions, withdiameters of2to3,um(probably theresidue ofdroplets containing more thanone spore) and1to2 jim(probably theresidue fromsingle-spore droplets). Aspredicted bythesimulation, the aerosol settled andprogressed downwind, withthenumberofsmalldroplets andparticles increasing in proportion totheheight anddistance downwind. Studies ofthechronological events occurringinmicrobial aerosols havebeenlimited toevaluating thesurvival ofcells suspended inthespray solution undervarious ambient environmental conditions (see, e.g.,references 2,8,9,and 11).Withthedevelopment ofmodelstopredict viable airborne microbial dispersion anddeposition ofan aerosol (see, e.g.,references 10,12-16), theestimation ofthedrift characteristics ofliquid droplets or evaporated particles (residue) froma sprayed microbial suspension becomes an important factor inbioaerosol research. Thedevelopment ofaerosol technology asdescribed previously (4-7, 17)provides an opportunity toestimate more detailed temporal drift characteristics ofliquid aerosol dropletsthatcontain a suspensionofviable microbes. The purposeofthis report istodescribe theestimated trajectory ofspore-containing aerosol droplets andtocompare this with an observed bacterial-spore aerosol drift pattern.

Balkumar Marthi

Papers

Artificial wind-gust liberation of microbial bioaerosols previously deposited on plants

Trajectory ofAerosol Droplets froma Sprayed Bacterial Suspension