What is your number? We all have numbers that are important to us as individuals—our social security number, our telephone number, maybe even our bed's sleep number. But there should be another number that is important to you, too, and that is an AQI number. The Air Quality Index (AQI) is a means of reporting daily air quality, and it is a measure of how clean or polluted air in a specific location is. The AQI number directly relates to the possible health and environmental effects of air, as well as the calculated health risks within a few hours to days after breathing it.
This is where AQI comes in and where veterinarians might be able to help their clients take a giant step toward successful management of horses with allergic inflammatory responses. AQI is calculated by the Environmental Protection Agency (EPA) focusing on the five major air pollutants regulated by the Clean Air Act. These pollutants are ground-level ozone, particulate matter, carbon monoxide, sulfur dioxide and nitrogen dioxide. Research has shown that these pollutants represent the greatest dangers to health, and the EPA has set national air-quality standards for them. The EPA makes measurements and calculations for all of these pollutants, and this information is then factored into an AQI number for a given location within the United States. A value of 100 is the national standard. Values below this number generally are thought to be satisfactory. Values of 0-50 are considered good, and values of 50-100 are moderate, meaning that only those animals and humans with pre-existing respiratory problems might experience health concerns. Values from 101 to 150 are considered unhealthy for sensitive individuals, and values from 150 to 200 are unhealthy for everyone. Levels beyond this are labeled very unhealthy and then hazardous and correspond to serious health concerns and emergency conditions.
The five major air pollutants merit a closer look because these different respiratory irritants are found in different locations across the country, and they seem to affect individuals differently. David Hurley, a Ph.D. microbiologist working at the University of Georgia College of Veterinary Medicine and exploring the interaction of various pollutant particles on respiratory health, points out that some horses, just like some humans, might have fungal trigger levels while others can have ozone trigger levels. These would be the levels of various irritants that initiate an inflammatory response in a specific individual.
Knowing more about the specific pollutants will help isolate and identify their effects.
Ozone (O3) is a gas emitted into the air and is created at ground level by a chemical reaction between nitrogen oxides and volatile organic compounds in the presence of heat and sunlight. Motor vehicle exhaust, emissions from industrial plants, chemical solvents and gasoline vapors are the chief sources that produce ozone. Ground-level ozone and ozone occurring in the atmosphere have the same chemical composition. Ozone that forms 10-30 miles above the earth's surface forms a protective layer to block the sun's harmful rays. This is considered good ozone while the same compound formed at ground level can irritate lung tissue and cause inflammation. Even low levels can cause aggravated asthma, reduced lung capacity and decrease exercise tolerance and increased susceptibility to infection. Repeated exposure can cause scaring of the lung tissue leading to permanent damage. This is considered bad ozone. Because ozone formation requires heat and sunlight, it is known as summertime irritant and commonly is found in high levels in urban areas. But ozone carries well in wind, and rural areas many hundreds of miles removed from the initial site of formation can be affected seriously.
Particulate matter (PM) is the term used for particles found in the air. These particles can be large enough and dark enough to be seen—as in dust, dirt, soot and smoke—or they can be so small that they can be detected only by electron microscope. Some particles come from engines emissions, factories, dust and dirt from construction sites, tilled fields, horse arenas, unpaved roads and from burning wood. Others come from chemical reactions from fuel combustion. These particles also can damage lung tissue and initiate inflammatory responses in sensitive individuals at even low levels. PM also is likely to cause significant throat irritation resulting in coughing, and it is the major cause for eye irritation and excessive ocular discharge, redness and irritation.
Carbon monoxide (CO) is primarily the result of burning vehicle fuels and, as such, is produced in large quantities in urban areas. CO causes intense irritation to lung tissue and can be lethal in high concentrations. Nitrogen dioxide (NO2) occurs when fuel is burned at high temperatures and is mainly produced by vehicles, electric utilities, and industrial combustion processes. Sulfur dioxide (SO2) is produced mainly by coal-burning electric utilities at a rate of nearly 13 million tons per year. In the air, the SO2 reacts with other chemicals to form small sulfur particles that gather in the lungs and cause tissue damage.
Since all of these pollutants can cause lung damage it is important to know how much of these irritants is in the air where you and your clients' horses live. The EPA maintains a Web site that can provide this information and will help you counsel your clients on management of these sensitive horses. By accessing www.epa.gov/airnow, you will enter the national AQI center site. This site explains the AQI and allows you to click on "Forecasts". This provides a map of the United States. Clicking on your city (or the nearest city shown) will give you a current forecast for air quality. The primary and secondary pollutants are listed along with a summarized health risk warning and a detailed forecast. Yesterday's conditions are available for trend comparison, and archive links are present to check today's conditions against those of last year's on the same date. These features are important when trying to set up a better management plan, for a COPD horse for instance. Many of your clients will report that a particular horse always seems to have trouble breathing or has reduced training days at a particular time of the year. What is it about the allergen exposure at that particular time? Is it a particular level of ozone for instance or a combination of heat, and particulate matter? Only by recording daily AQI levels and correlating them to that horse's breathing and performance record will you be able to see and use trends. The Airnow site also allows you to bring up a map of a specific area and to see a graphic representation of the AQI changes occurring throughout a single day mapped out in 20-minute intervals. A calculated prediction of the next day also is available. This can be of value in deciding if and when to work a horse on a specific day. If the AQI data—using either the archived data for usual conditions for that location or the predictive map—shows that air quality will be good until 11:00 a.m. and then will deteriorate until after 8:00 p.m., then you should suggest that any exercise or use of that particular horse occur only when the air quality is acceptable. With consistent use and attention to a horse's responses the AQI data can yield very specific guidelines. Ozzie is a case in point. This dressage horse has been suffering with COPD in the Atlanta area for years. He is generally controlled with oral Albuterol but still has intense flare-ups throughout the summer and cannot be ridden, and he must be monitored closely during these allergic episodes. With use of the Airnow site and through his owner's observations, it has been determined that Ozzie's number is 61. Below 50 he can be worked hard, does not need to be treated and shows no problems. Fifty-one to 61 requires daily Albuterol and a reduced work level. Exercise when the AQI is above 61 triggers a reaction, and Ozzie will take days to return to normal. Additionally, it has been determined that Ozzie reacts most strongly when the primary pollutant is particulate matter rather than ozone, so a 60 with high ozone is not as bad for this horse as a 60 with high PM. This wealth of data has allowed Ozzie's owner to get more useful work from her horse during a difficult time of the year while doing a better job of controlling his health issues. Hurley agrees that this type of AQI data management is the way of the future.
"Eventually it is hoped that research will be able to identify the particular pattern of allergic triggers for individuals," Hurley says. "Products such as leukotrine inhibitors can help to stop those triggers form causing these severe allergic responses."
Until that point, using the EPA data to find the AQI number that works best for affected horses may be the best management plan available.