If there are no contaminants in the air, the quality is perfect. Not many places exist with no contaminants. At the pre-college level, detection of gaseous contaminants such as NOx or SO2 pollutants is difficult without donated equipment. Particulate matter in ambient air is readily availible in most locations and relatively easy to sample. These can all be readily sampled with a vacuum cleaner and the kleenex holder suggested in the Berkeley Lab experiment.
Studies can be of both total mass of sample and analysis of what is cught by the filter.
In the spring time pollen collected can be examined by examination through a high powered light microscope. The same filter system can be used to collect the combustion products of cigaretts by attatching the top half of a plastic water or soda bottle to the filter holder. The collected tars and smoke particles are colorful to say the least.