Effect of central air conditioning and meteorologic factors on indoor spore counts

We have studied the effect of residential central air conditioning on indoor spore counts. The air of 6 pairs of homes (air-conditioned and non-air-conditioned) was sampled volumetrically 4 times daily for 3 consecutive days at 2-hr intervals in the kitchens, bedrooms, and basements with an Anderson sampler. Nearly simultaneous samples were taken outdoors at the same intervals. The total spore count was significantly lower (p less than 0.05) in the kitchens and bedrooms of air-conditined as compared to non-air-conditioned homes. Logarithmic conversion of the total spore count showed significant reduction in all indoor locations of air-conditioned homes. Multiple regression analysis revealed the lower relative humidity of air-conditioned homes to be associated with the lower spore counts. There was no difference in the percent concentration of the major genera within both types of homes. Since reducing the influx of outdoor spores decreases the total spore count without altering the relative concentration of the genera whereas filtration preferentially removes the larger spores, we conclude that the major mechanism in reducing spore counts in air-conditioned homes is the closed windows, although the lower relative humidity and perhaps filtration are also associated with lower spore counts.