Quote Originally Posted by pjt View Post
Adding to the debate.....What effect does air temp/hum have on the suspension of particles? Does dry air allow more floating of particles? Does moist air have the opposite effect? or Is there no difference?
Pete
Temperature, Humdity and Dust are very interesting companions.

John has already provided the main temperature-dust correlation but the dust-humidity one has a bit more to it. The guys adding window tint are only interested in visible dust which is reduced by removing charge from the bigger particles by squirting water vapour into the air, but irrespective of the temperature, increased humidity dramatically increases the number of invisible particles present in the air and that effect is easily detected by a particle counter. For example I see as much as a five fold increase in the small particle background of dust in sheds that are close to the ocean compared to those that are not. This happens because the zillions of sub-0.1 micron particles can absorb enough water and start to clump together to become >0.1 micron particles. In addition ocean roughness also increases particle counts as the waves generate droplets that evaporate and leave salt particles suspended in the air. This is a trap for people using particle detectors and my guess is that there are some (perhaps foolish) decisions made that did not take these into consideration. All particle measurements should be recorded with along with temp and humidity data just in case these could contribute to the results.

One question worth asking is, what is the effect of the sub-0.1 micron particles turned into bigger particles by humidity. This appears to be unknown. A sub-0.1 micron particle surrounded by a water jacket turning it into a 0.5 micron particle is likely to be less harmful than a 0.5 micron particle composed entirely of wood. OTOH a 0.5 micron particle resulting from clumping of sub-0.1 micron particles is likely to be just as bad.

Terrestrial temperature and dust levels are highly correlated which enable dust to be used as a paleothermometer in environmental reservoirs like polar ice. In ice cores that go back in time through a number of ice ages the levels of dust in the ice vary with temperature. However the effect is the reverse to what one might believe. High temperatures means most of the land is covered with seawater and vegetation which means less exposed land so less dust. During ice ages the amount of vegetation decreases and the ocean levels fall dramatically (can walk across Bass Straight) exposing large areas of continental shelf which produces a lot of dust.