Three-year investigation of the natural airborne bacterial flora at four localities in sweden

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Abstract
The concentration of airborn bacteria was recorded during a period of 3 yr at 4 localities: in an agricultural district with an average of 99 (range, 2-3400) bacteria/m3, in a coastal area with an average of 63 (range, 0-560) bacteria/m3, in a city park with an average of 763 (range, 100-2500) bacteria/m3; in a city street with an average of 850 (range, 100-4000) bacteria/m3. At all 4 localities the bacterial concentrations varied within broad limits, but an annual periodicity with high average counts found during summer and autumn could be seen. The influence of certain meteorological factors on the number of airborne bacteria is also reported. Rain or high relative humidity caused a decrease in the bacterial counts, while high temperature or high wind velocities increased the counts. The particle size distribution for the 4 localities showed that about 50% of the particles carrying bacteria were larger than 8 .mu.m.