Because of the location of the three places, there are people to service a lot. We need to check the air quality in areas that have pollution or disease-causing substances with this service?
Because the three locations is that people who use the service a lot. We therefore want to check the air quality in areas that are polluted with pathogens or chemicals used or not.
Because the place is the source of the three places people into service a lot. We need to check the quality of the air in the area that was polluted or substances that cause disease to users or not.