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Air Quality Background Information

Page history last edited by ashley.collier@... 10 years, 3 months ago


Air Quality Background Information


     For more detailed information on outdoor pollutants or indoor air quality, try these links


     http://epa.gov/airquality/urbanair/ or http://www.epa.gov/iaq/ia-intro.html 



The Pollutants: 


CO2 - Carbon Dioxide  


The primary source for CO2 indoors is human exhalation.  This compound is a byproduct of human metabolic activity and might be more likely to build up in areas with a lot of people or poor ventilation.  Other sources include those resulting in combustion byproducts: car exhaust, fossil fuel power plants, leaking furnaces, cigarette smoke, etc…  CO2 can be considered one of the primary products of combustion; complete (or ideal) combustion results in CO2 and H2O, as well as, energy.  CO2 is a major greenhouse gas and contributor to climate change, for more information, check out the climate change section below.


(http://www.idph.state.il.us/envhealth/factsheets/indoorairqualityguide_fs.htm; http://www.health.state.mn.us/divs/eh/indoorair/co2/index.html)


Reference Levels: 


300 - 400 ppm: typical levels outdoors


600 - 1000 ppm: typical levels in properly ventilated buildings


> 1000 ppm: this range suggests inadequate ventilation and could result in health effects associated with high CO2 (e.g., fatigue), this may also indicate that other pollutants might be building up as well 






CO - Carbon Monoxide 


This pollutant is a result of the incomplete burning of fuels (or the incomplete combustion of natural gas, coal, wood, etc...).  Some common sources of carbon monoxide are unvented gas space heaters, gas stoves, fireplaces, generators, gasoline-powered equipment, including automobiles.  In particular, dangerous sources can be old or poorly functioning combustion devices.  In certain quantities, this pollutant can pose immediate threats to human health.



Reference Levels:


             .5 - 5 ppm: typical range in homes with no gas stoves


             5 - 15 ppm: typical range in homes with gas stoves


             1-70 ppm: Prolonged exposure to this range typically does not cause symptoms in healthy people


             > 70 ppm:  Symptoms of CO poisoning will begin to appear in healthy people


             > 150 - 200 ppm: Dangerous levels of CO exposure


(http://www.epa.gov/iaq/voc.html#Levels%20in%20Homes; http://www.cpsc.gov/cpscpub/pubs/466.html)



VOC's - Volatile Organic Compounds 



The composition of VOC’s allow them to volatilize or evaporate (from solid or liquid form to a gaseous form) under normal indoor temperature and pressure conditions, which makes them easier for people to accidentally ingest, thereby posing a threat to human health.  They are present in a wide variety of products from cleaning supplies and pesticides, to building materials, paints, and office equipment.  There are literally hundreds of VOCs and they include everything from compounds emitted by pine trees (these are what you smell in a forest) to those emitted in gasoline vapor (benzene, for example).  These compounds can also range from harmless, to toxic, and even carcinogenic. 



Reference Levels:


Unfortunately very little research has been done on overall VOC levels and their impacts, studies do indicate that indoor levels are on average 2-5 times higher than outdoor levels.  Although there are many VOC’s that are regulated individually; formaldehyde, for example, has a Permissible Exposure Level of .75 ppm as determined by OSHA.  Individual compound regulation typically occurs in workplaces.





O3 - Ozone 


The effects of ozone varying depending on where it is located; in the upper regions of earth’s atmosphere it occurs naturally and shields the earth from the sun’s ultraviolet rays.  However, at ground level it poses a threat to human health as a pollutant, to be precise it is a respiratory irritant.  Ozone is formed when VOC’s and nitrogen oxides react in the presence of sunlight, which is why ozone is typically highest on sunny days in urban environments.  The sources of ozone forming compounds include emissions from vehicles, construction equipment, industry, and some consumer products, however, ozone is never directly emitted itself.  Another factor to consider, is that ozone is more prevalent outdoors than indoors, and should be considered when engaging in outdoor physical activities. 




Reference Levels:


< .059 ppm: good levels


.060 - .075 ppm: moderate levels


.076 - .095: unhealthy for sensitive groups (young children, elderly, and those prone to respiratory issues)


.096 - .115 ppm: unhealthy levels for all groups


> .116 - .404 ppm: very unhealthy levels for all groups




NOx - Nitrogen Oxides 


This measurement refers to the NO and NO2 levels in the air, both of which are toxic.  Indoors, these compounds primarily result from combustion reactions (gas stoves, gas heaters, tobacco smoke).  Outdoors, NO and NO2 come primarily from emissions (car exhaust, or industry).  They pose a threat to human health both in their NO and NO2 forms, and because NO2 is a contributor to ozone production. 


Reference Levels:


Currently there are no standards or limits for indoor air levels of nitrogen oxides; for reference, levels in homes without combustion appliances are typically half of outdoor levels, while homes with combustion appliances can have levels exceeding outdoor levels.  The outdoor annual average limit for NO2 is set at .053 ppm.







Other Important Quantities 




Temperature & Humidity:


     These measurements serve several different purposes.  First of all, due to the relatively high flow rate through the monitors, we can use these measurements to gain a general understanding of the weather conditions accompanying our data.  Additionally, several of our sensors are temperature and humidity sensitive and having this data allows us to correct for these impacts during post-processing.


Wind Speed & Direction:


     Wind speed and direction can assist in understanding pollutant transport or possibly even in locating a specific pollutant source.





     GPS data allows for the plotting of mobile data on maps, which can enhance spatial understanding of air quality information.




A Note About Air Quality Units of Measurement



          Pollutant levels are typically measured in ppm (parts per million) or ppb (parts per billion).  To help you understand this type of measurement - imagine a million sealed water bottles, if you had 400 ppm of CO2, that would mean 400 out of the million bottles would be filled with pure CO2 and the rest with air and some other constituents.   The same analogy holds true for ppb, except that one billion bottles should be imagined instead of one million.  Another common unit of measurement is mg/m3, this implies a particular weight for a given volume of space.  Although these units can be used with gases they are more typically used with particulate pollutants.  



Climate Change


     Certain gases (CO2, CH4, O3, N2O, and water vapor) are also air quality concerns due to their abilities as greenhouse gases.  Greenhouse gases have the ability to absorb and re-emit outgoing long-wave radiation from the earth, which results in an overall warming effect.  The diagram below illustrates this effect.  Some of these gases, such as water vapor, exist naturally in the atmosphere and we only effect their concentration through indirect means.  However, others, such as ozone and carbon dioxide, are directly emitted by or as a result of human activity, and increasing the rate at which we are putting them into the atmosphere increases our risk of impacting global climate. 





Click here for more information on Climate Change.


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