Indoor air quality

By Daniel Mendoza

Inversions are natural events due to cold temperatures and our surrounding mountains (for a more detailed explanation, take a look at CATALYST’s January 2018 issue). When air becomes stagnant, pollution, which normally gets ventilated away, ends up trapped. This causes us to earn a dangerously high rank in particulate matter (also known as PM2.5) levels in the country.

Luckily, newer technology has been helping reduce pollution levels, including cleaner industrial sources and fuels, more efficient (and even electric) vehicles. You can do your part by taking public transit instead of driving (see CATALYST, January 2019).

We may bemoan the air outside, especially when we see layers of soot. However, outdoor air quality is only a part of the equation. We spend, on average, about 90% of our time indoors—be it at home, office or school—and this number increases during the winter as people avoid cold temperatures. That means that on a given day we are indoors for over 22 hours and this is where we should be most concerned about the air we breathe.

Many scientific studies have focused on the impact of outdoor air quality on health, but relatively fewer have focused on indoor air quality. The reason is simple: Outdoor air quality is much more easily measured and has fewer factors affecting its variability. An entire neighborhood can have similar air quality.

But think about your house for a minute. Say you forgot to turn off the oven and you burn dinner—the kitchen and maybe the adjoining rooms are smoky, but it’s okay upstairs. If someone in your household enjoys using a lot of perfume, hairspray or air freshener, those tiny droplets are technically particulate matter and may have negative effects within those rooms, but the remainder of the house would be mostly unaffected.
So how can we protect ourselves? The answer depends on how you heat your home in the winter and your budget.

Forced air heat
Salt Lake City homes are most commonly heated by forced air. Forced air takes in air from the outside, heats it in a furnace and redistributes it through air ducts across all rooms in a house. The main disadvantage of forced air is that the air it’s bringing in could be contaminated, particularly during inversions.

The incoming air passes through a filter. You’re familiar with heading to the store to buy new filters, right? Many people buy the most inexpensive filters available in multi-packs. This is a mistake, especially if you want to breathe.

Filters are rated using a scale called minimum efficiency reporting value (MERV) rating which specifies the efficiency of trapping particles of specific sizes—the higher the MERV rating, the smaller particles it traps. These are the particles we especially don’t want in our homes.

A typical inexpensive filter has a MERV rating of 4 to 8. These are known as “rocks and logs” because that’s essentially what they can trap. For maximum health benefits, providing your furnace motor can handle it, buy filters with a MERV rating of 13.

There are also electrostatic filters which essentially charge the air as it goes through and traps the pollutants in that manner. These need to be washed at least every month but are very efficient.

Heating via radiators involves heating water in a boiler and piping it around the home to radiators, which radiate heat into the room.

For radiator-heated homes, stand-alone air filtration units are available in various sizes. Place them strategically in the most-used areas, especially sleeping areas. Our noses can filter some air pollution, but when we sleep, we tend to breathe through our open mouths which do not filter the air.

Look for stand-alone units that provide sufficient coverage for the intended area, whether it be a room or one floor. It is likely that a multi-story house will need a unit for each floor as it would be difficult to circulate air across floors.

Air purifiers and humidifiers
Given our current knowledge of particles and health impacts, a unit with HyperHEPA filtering could have the most benefit. While HEPA filtering units are an inexpensive option, they will not trap the smallest of particles that could permeate deeper into our lungs and potentially our bloodstream.

A lower-cost solution is a high-output humidifier. Humidifying your house offers three distinct benefits:
1. Dry air, which is even dryer in the winter, has obvious effects on our body, such as dry skin. This drying also happens in our respiratory system and can irritate air passages.Whenever you have a cold or flu, you are told to stay hydrated as this helps release mucus and reduce irritation. A humidifier provides a similar benefit.

2. Humid air is also able to retain heat better than dry air which means you may be able to reduce your heating bill in the winter—and who doesn’t want that?

3. Lastly, higher humidity can help condense particulate matter and reduce indoor concentrations. When our inversions happen, we all want it to rain or snow so the smog clears up. Higher humidity may produce a similar effect indoors.

So, when it comes to improving the air quality inside your home, it starts with how your house is heated. Many companies produce furnace filters and air purifying units which, for the most part, are beneficial. Make sure you focus on the areas you spend the most time in, especially sleeping areas.

As for going outdoors: Consider wearing a high-quality breathing mask when you must go outside during bad air quality days to lessen your exposure.

Daniel Mendoza works in the Pulmonary Division and Department of Atmospheric Sciences at the University of Utah. His research entails the quantification of urban emissions, subsequent pollutant exposure, and health outcomes. He was a recipient of the University of Utah’s Sustainability Leadership Research Award in 2019.

This article was originally published on December 30, 2019.