Impact of Outdoor Seasonal Changes on Indoor Air Quality

Impact of Outdoor Seasonal Changes on Indoor Air QualityManaging indoor air quality is a difficult job because the variables are constantly changing and settings need to be adjusted to account for these changes. Some changes can be easily controlled, such as occupancy rate, housekeeping procedures, temperature control, and moisture barriers. One variable that is unable to be controlled and must be managed individually is seasonal changes.

However, even though you may not be able to control the seasons, there are predictable patterns that come with each season that you can use to help you prepare, and will make it easier to maintain indoor air quality.


During the hotter summer months there is a decrease in pollen, but mold and dust increase significantly. The temperature also continues to rise, and in many areas humidity levels are at a yearly high. Within urban areas an issue during the summer is an increase in ozone and outdoor pollution levels building up, some cities can create a bubble around themselves where the temperature and pollution levels are significantly higher than the surrounding areas.

Air conditioners are also used more during the heat of summer, and if they are not cleaned and operating correctly they can grow mold within the ventilation system, which then blows throughout the building. Air conditioners also pull humidity out of the air, and the change from high to low humidity for people entering the building can cause sinus issues for at risk patients.

A poorly maintained ventilation system will have significant operating costs during the summer, and will not properly mix the correct amount of fresh air into the system to manage humidity and temperature levels.


In the Fall mold levels reach their highest for the year as grasses and leaves begin to decay, and some plants put out pollen. Temperature fluctuations mean that ventilation systems will have days when they are operating inefficiently and are not able to manage the air temperature and humidity.


Outdoor pollen and contaminants are usually at their lowest during the winter, and frozen ground and air means that mold is not present. Humidity is typically lower during this time of year, which actually causes issues with indoor air quality. Indoor humidity is lower than outdoor humidity due to the heating system, and low humidity can cause the mucous membranes to dry out and can increase the risk of respiratory infections.

People are also indoors more, which increases the chance of an airborne pathogen entering the ventilation system.


Everything starts to increase during the spring months, including pollen, dust, mold spores, and temperature and humidity levels. These create an increase in the symptoms of allergy attacks and illness, which can be brought into the building. Oddly, as the temperature and humidity increase there are fewer colds and respiratory infections, but other illnesses will take their place


Need help planning your indoor air quality procedures for the changing seasons?  Contact us now to see how we can help!



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