Tag Archives for " ozone "

OH, the detergent of the atmosphere, and OH-, the ion that cleanses our homes’ air

Did you know that earth’s atmosphere is self-cleaning, to an extent?  We would be A LOT worse off if it wasn’t.

OH, the hydroxyl radical, is the most important oxidizing species in the atmosphere.  In this article, we’re going to discuss how it’s formed in nature, what it does, and how it’s different from the hydroxyl ion OH- that is formed in bipolar ionizers.  

You’ve probably heard that there is ozone in the earth’s atmosphere.  The majority of ozone is found in the stratosphere (about 10-25 miles above the earth), shielding us from the sun’s UV light and cosmic radiation.  This is where ozone can be destroyed by molecules that contain chlorine and bromine, such as chlorofluorocarbons (CFCs). (EPA.gov) About 10% of the ozone is found a bit lower, however, in the troposphere (where clouds are formed and planes fly).  In the troposphere, ozone performs a very important function by being a primary ingredient for the production of OH.  Here, UV energy from the sun (mostly in the UV-B range of 290-310nm)(Treatise on GeoChemistry, ch.5.5.9.1 Chemistry of the Hydroxyl Radical (OH) in the Troposphere), breaks down ozone (O3) into O + O2.  Then, in the presence of water vapor (there’s very little water vapor in the stratosphere, so this has to happen in the troposphere), the lone O molecule reacts with H2O to form 2 molecules of OH (hydroxyl radical).  

In chemistry, a radical, also called free radical, is a molecule that contains at least one unpaired electron.  OH is a radical which is highly reactive because of the configuration of electrons in its outermost shell.  Normally, atoms and molecules prefer to have 8 electrons in their outermost shell, making them most stable (called the Octet Rule), but they will compromise and share electrons if necessary.  OH has 7 electrons in its outer shell: 6 electrons are from the O atom and 1 electron from the H atom.  Each electron has a negative charge, but it is balanced by the same number of protons in the nuclei of the atoms, so that the total “charge” of the molecule remains neutral.  Electrons also like to be “paired”, and although each has a negative charge, they have opposing spin directions which causes them to seek to be “paired” with another electron.  The OH molecule constantly seeks one more electron to “pair” with the 7th electron in its outer shell.  OH only survives for nanoseconds after it is formed–because it can immediately steal that missing electron from most of the chemicals found in the troposphere.  This reaction of the OH with other molecules is called oxidation. 

(Oxidation: Despite the name, the presence of oxygen is not a requirement in an oxidation reaction.  The reaction is part of a transfer of electrons between two substances.  Oxidation occurs simultaneously with reduction in a type of chemical reaction called a reduction-oxidation or “redox” reaction.  The oxidized atom loses electrons, while the reduced atom gains electrons.  On earth, oxidation is usually an undesirable reaction.  Oxidation is another name for rust, corrosion, and breakdown of materials around us and in us.  Our bodies produce “anti-oxidants” to prevent breakdown of our cells. ) 

There are limitless reactions that can happen in the atmosphere, but OH reacts primarily with carbon monoxide (40%) to form carbon dioxide. Around 30% of the OH produced is removed from the atmosphere in reactions with organic compounds and 15% reacts with methane (CH4). The remaining 15% reacts with ozone (O3), hydroperoxy radicals (HO2) and hydrogen gas (H2). (Oxidation and OH Radicals)  With its supreme oxidation potential, hydroxyl radicals can react with molecules and chemicals that are otherwise extremely stubborn and resist oxidation. (Hydrogenlink.com)

Since OH is primarily formed with energy from the sun, OH production mainly happens during daylight hours.  The following map is a snapshot of a model showing how OH is generated as sunlight illuminates a rotating earth.  (The Atmosphere: Earth’s Security Blanket)  Because OH is so short-lived, it’s really hard to detect, so the formation or degradation of other chemicals is used to determine how much OH is in the atmosphere at any one time.  For example, this model is generated from the Tropospheric Emissions Spectrometer (TES) equipment on a NASA satellite.  TES measurements of a number of other chemical elements influenced by OH, such as ozone, carbon monoxide and nitrogen dioxide, have enabled scientists to better represent OH in these models.

Did you know that humans also generate OH indoors? (Science Daily)  Indoor air can have higher (but not dangerous) levels of ozone, which reacts with certain oils on our skin. The reaction releases a host of gas phase chemicals containing double bonds that react further in the air with ozone to generate substantial levels of OH radicals.  It’s a very new discovery (2022), which was aided with extensive computer modeling.  This is important to know, because although they are great to have in the upper level of the troposphere,  we don’t want high levels of hydroxyl radicals indoors.  They can damage tissue and frequently initiate chain reactions with other radicals and VOCs, able to produce harmful chemicals like formaldehyde. 

It’s not the heat, it’s the humidity air pollution!

Decades ago, when the meteorologists predicted extreme heat, it seemed they only advised on the necessity to stay out of the sun, drink more water, and cool off more frequently (stay in the pool, yayyyy!).  Now, heat advisories come with more sinister warnings about air pollution levels, and the outdoors are less fun.  How did that happen?  The answer lies in meteorology and chemistry, all cooked up in our atmosphere.

Low-pressure systems are quite famous for moving rapidly across the US and bringing devastating weather like severe thunderstorms, hail and tornadoes.  They can also sweep pollutants like smoke and smog to other states.  High-pressure systems, on the other hand, typically cause stagnant air, which can concentrate pollutants over one area.  (scied.ucar.edu)  A “Heat Dome” is an area of high pressure that parks over a region like a lid on a pot, trapping heat. (National Geographic) A Heat Dome caused about 600 deaths in June 2021 in the Pacific NorthWest as a 1-in-1000-year event.  The heat, which broke Portland’s all time record of 107 degrees, was bad enough, but extreme heat combined with stagnant air during a heatwave increases the amount of ozone pollution and particulate pollution. (metone.com)  Here is where the chemistry comes in.

“Ground-level ozone pollution forms when heat and sunlight trigger a reaction between two other pollutants, nitrogen oxide and volatile organic compounds — which come from cars, industrial facilities, and oil and gas extraction. High temperatures therefore make ozone pollution more likely to form and harder to clean up. Drought and heat also increase the risk of wildfire, which can make air quality worse as smoke drives up levels of fine particulate matter — also known as PM2.5, or soot...Both ozone and PM2.5 carry major health risks. Ozone can cause acute symptoms, including coughing and inflamed airways, and chronic effects, including asthma and increased diabetes risk. PM2.5 exposure can lead to an increased risk of asthma, heart attack, and strokes. Globally, long-term exposure to PM2.5 caused one in five deaths in 2018, including 350,000 deaths in the United States.” (Heat waves can be life-threatening for more reasons than one)

Because of the increase in cars and industry, extreme heat forecasts are not just requirements to have bottled water and popsicles on hand and check that our elderly neighbors’ air conditioning is working.  It’s a time to make sure that those who have asthma, heart and vascular conditions stay indoors, and that you take the proper air pollution precautions, too. 

Unlike outdoor air filled with wildfire smoke, ozone and smog are not as visible and may not affect everyone immediately, but they are dangerous pollutants and shouldn’t be allowed in our homes.  Here are some steps you can take to prepare for that heatwave, and the resulting air pollution that often accompanies it!  

• Seal doors and windows with weatherstripping, caulk and door sweeps.  

• Find out how to adjust your HVAC system accordingly: you’ll want to close the fresh air intake and change over to recirculation, no matter whether you have central AC, a window air conditioner or portable air conditioner.

• Purchase extra MERV 13 filters for your HVAC system, to be used on poor air quality days (caution: read our post on HVAC filters first, as using a filter with too high MERV rating can damage your system). 

• If you live in an apartment building or condo with little control over the HVAC, consider purchasing vent filter material so you can place them in the vents into your space.  The filter material can prevent smaller particulates in smog from entering.  Carbon vent filter material will neutralize many VOCs as well.

• Purchase a HEPA air cleaner (non-ozone producing type) and be sure to have an extra filter or two on hand.  The use of a HEPA filter will take much of the damaging fine particles out of the air you breathe!  Whenever there is bad air quality outside, run the cleaner/purifier on high for an hour and thereafter at "quiet"/medium setting (Wirecutter).  You can check out our post on standalone HEPA filters as a purchase guide.  If you can't purchase one, make one: there are many videos and instructionals online for DIY air cleaners; most only require one or more filters, a box fan, and some cardboard and tape.

• Keep a stash of N95 respirator masks on hand.  These are a good source of protection if you have to go outside, or if power is cut to your home and indoor air quality gets bad as well.  The “95” means it blocks out 95% of particulates.   

• Keep canned and non-perishable food on hand, so that you don’t have to cook during periods of bad air quality.  Cooking indoors increases small particulates and vapors in the air, and you won’t want to turn on your stove exhaust, as that will draw polluted outdoor air into the house.

• If air quality is very poor (check next point), you’ll want to evacuate to a place with clean, filtered air, like indoor malls, libraries, community centers, civic centers and local government buildings (sfgate.com). 

• Check your local air quality and receive updates from airnow.gov . Using an Air Quality Index (AQI) as a measuring tool ranging from 0-500, your local forecast and larger maps can be color coded to show whether an area is good (green), moderate (yellow), unhealthy for sensitive groups (orange), unhealthy (red), very unhealthy (purple), and hazardous (maroon).

How droughts can even impact your air

It’s been an unusual year.  In the southeast US, temperatures have been above normal with extended periods of no rain.  In the west, Lake Mead and Lake Powell have lowered by nearly 75% of where lake levels once were as the country's two largest reservoirs.  The Colorado River, which supplies these lakes, is used by seven surrounding states, and for decades annually the region was taking out about 1 million acre-feet of water more than the river was providing (Los Angeles Times).  Much of the country is in drought, and the Southwest is experiencing a megadrought–one it has not seen in 1,200 years. 

What is drought?  Drought arises only after a prolonged (>week) period of precipitation shortage that causes soil to dry up, and these period(s) may reoccur monthly.  Further, the prominent feature of drought is water deficit in both the atmosphere and the land component (e.g., soil and vegetation), resulting from the combination of precipitation shortage and increasing evapotranspirative water loss driven in part by high temperatures.   (2017 study).  When drought hits home, it’s more than water restrictions on your lawn. Here are some of the effects: 

• Droughts increase ozone and PM2.5. A study released in 2017 examined air quality during 4 severe droughts and found that elevated ozone and PM2.5 are attributed to the combined effects of drought on deposition, natural emissions (wildfires, biogenic volatile organic compounds (BVOCs), and dust), and chemistry. In our post “It’s not the heat, it’s the humidity air pollution”,we noted the correlation between extreme heat and ozone.  Here are some other facts brought forth by the 2017 study: 

• Meteorological conditions/extremes likely to co-occur with drought that are also associated with higher pollution levels. For example, high ozone is more likely to occur with high temperature and low RH (2016 study; 2017 study, 2016 study 2)

• more frequent stagnation and heat waves could explain up to 40 % of the ozone and PM2.5 enhancements during drought

• Since anthropogenic sources of ozone and PM2.5 have decreased significantly since 1990, the ozone and PM2.5 enhancements during drought are largely responses of natural processes from the land biosphere and abnormal atmospheric conditions. 

• Droughts affect plants and their interaction with atmospheric ozone in complicated ways.  Some plants take in ground-level ozone, while other plants emit isoprene, a VOC that reacts with other atmospheric chemicals to create ozone. (Scientific American).  While studying the 2011-2015 drought in California, scientists found that: 

• Dry conditions caused the plants to restrict water loss by closing their stomata (pores), which means taking in less ozone (ozone levels rose). Absorption did drop by about 15% during the most severe years of the drought.

• Plants and trees were able to sustain isoprene production during the first three years by drawing on their carbon stores; isoprene helps them against heat stress. 

• After 4 years, isoprene production dropped, and so did ozone (by 20%).  

• Drying lakebeds (like the Great Salt Lake in Utah) expose people to toxic elements like arsenic when dust storms pick up lake bed dust, which are residuals of pesticides and agricultural chemicals that migrated into the lake over many decades.. (New York Times)  Another dried lake that causes air quality problems is Owens Lake in California, which is the country’s largest source of PM10 (geochange.er.gov).

• Droughts can increase transmission of soil and dust-transmitted diseases like Valley Fever, which is coccidiodomycosis (Cocci for short).  Dust that is liberated from the soil during digging activities or dry, windy conditions can carry the fungus, which workers or residents can breathe in.  It causes symptoms like fever, cough and tiredness, but can occasionally be serious or deadly.

• Trees and plants weakened by drought are more vulnerable to pests and disease, which can kill large numbers of them. Plants that succumb to drought and die cause several problems:

• they turn from absorbing ozone and CO2 to emitting carbon via CO2.  

• Dead plants and trees increase the risk of wildfires.

• Droughts impact electric power generation systems (the Grid)in the following ways (americanscientist.org):

• Hydropower is reduced because of low stream flow

• Demand for electricity increases because increased cooling is needed in homes and offices 

• Fossil-fuel plants (coal, natural gas) must increase production of electricity.

• This means that air pollution increases during drought due to our electric power generation system. IF changes can be made to shift to “cleaner” generators (ie. natural gas instead of coal) during drought, it is generally better for air quality. 

In all, drought is a serious, complicated blight on both the land and the air, which we at HypoAir have felt for some time because California has been in long-term drought.  Finding ways to reduce water and energy consumption helps everyone, so don’t wait until regulations forces change–here’s a list of ways you can help your community and family before and during drought.  However, it’s the unseen increases in ozone, PM2.5, fungus and other forms of air pollution for which the public generally doesn’t prepare.  Here are some ways you can be smarter about air pollution from drought:

• Continue to work on air sealing your home

• Have extra MERV 13 furnace filters, air purifier filters, and filter media on hand so that you can change these more frequently

• Have N95 respirators on hand for the immune-impaired who need to go outside 

• Be cautious about excavation and construction work in areas where Valley Fever is a risk (wear an N95 mask if necessary)