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Air Quality in Winchester

Air Quality Index

How clean is the air in your metropolitan area or county? Use this map to find out.

The U. S. Environmental Protection Agency (EPA) has provided a scale called the Air Quality Index (AQI) for rating air quality. The AQI scale is based on the National Ambient Air Quality Standards (NAAQS) and is described in the Code of Federal Regulations, Part 58, Appendix G. This map is based on the EPA AQI scale.

The latest AQI imagery available is for August 17, 2017 as of 11:10 pm EDT (Eastern Daylight Time). Click on any of the boxes on the image for a detailed listing of that monitoring site.
You can also view a tabular presentation of the Air Quality Index (AQI) Report for the entire state.

Sites outside the Winchester Metropolitan Area will appear dimmer than sites within the area. You can still select these sites to see data collected at them.

PLEASE NOTE: Data in this image is collected from Virginia DEQ air monitoring sites, local agencies, and private monitoring networks. This data has not been verified by the Virginia DEQ or the responsible entity and may change. While this is the most current data, it is not official until it has been certified by the appropriate technical staff. This image is updated hourly.

The image above shows the Air Quality Index (AQI) ratings for each of the NAAQS pollutants that are measured real-time and the critical pollutant that is driving the AQI rating in each where pollutant levels are monitored by the Virginia DEQ. The critical pollutant is the pollutant with the highest AQI rating measured in the area. The image is updated each hour and covers the period from midnight through the indicated ending time.

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Which Pollutants Can I Monitor Using the AQI?

There are five pollutants that go into the Air Quality Index: ozone, carbon monoxide, sulfur dioxide, nitrogen dioxide, and particulate matter. In the image above, each monitoring area is represented by a small box which is color coded to match the AQI rating for the day (see Interpreting the AQI). Inside the box, the pollutant that is driving the AQI rating is identified by its abbreviation (see the table below). At the bottom of each box is a small legend that indicates which pollutants are actively measured in that area. Each of the smaller boxes is color coded to match the AQI rating for that specific parameter. Please note that not all pollutants are measured in all areas or at all sites. The table below briefly describes each pollutant that goes into the AQI.

OzoneO3Ozone is a form of oxygen with three atoms instead of the usual two atoms. It is a photochemical oxidant and, at ground level, is the main component of smog. Unlike other gaseous pollutants, ozone is not emitted directly into the atmosphere. Instead, it is created in the atmosphere by the action of sunlight on volatile organic compounds and nitrogen oxides.

Higher levels of ozone usually occur on sunny days with light winds, primarily from March through October. An ozone exceedance day is counted if the measured eight-hour average ozone concentration exceeds the standards.
Carbon MonoxideCOCarbon Monoxide (CO) is a colorless, odorless, very toxic gas produced by the incomplete combustion of carbon-containing fuels, most notably by gasoline powered engines, power plants, and wood fires. CO can cause harmful health effects by reducing oxygen delivery to the body's organs (like the heart and brain) and tissues. At extremely high levels, CO can cause death.
Sulfur DioxideSO2Sulfur dioxide (SO2) is one of a group of highly reactive gasses known as "oxides of sulfur." The largest sources of SO2 emissions are from fossil fuel combustion at power plants (73%) and other industrial facilities (20%). Smaller sources of SO2 emissions include industrial processes such as extracting metal from ore, and the burning of high sulfur containing fuels by locomotives, large ships, and non-road equipment. SO2 is linked with a number of adverse effects on the respiratory system.
Nitrogen DioxideNO2Nitrogen dioxide (NO2) is one of a group of highly reactive gasses known as "oxides of nitrogen", or "nitrogen oxides (NOx)". Other nitrogen oxides include nitrous acid and nitric acid. While EPA's National Ambient Air Quality Standard covers this entire group of NOx, NO2 is the component of greatest interest and the indicator for the larger group of nitrogen oxides. NO2 forms quickly from emissions from cars, trucks and buses, power plants, and off-road equipment. In addition to contributing to the formation of ground-level ozone and fine particle pollution, NO2 is linked with a number of adverse effects on the respiratory system.
Particulate MatterPM-2.5
Particle pollution (also called particulate matter or PM) is the term for a mixture of solid particles and liquid droplets found in the air. Some particles, such as dust, dirt, soot, or smoke, are large or dark enough to be seen with the naked eye. Others are so small, they can only be detected using an electron microscope. Particle pollution includes inhalable coarse particles, with diameters larger than 2.5 micrometers and smaller than 10 micrometers and fine particles, with diameters that are 2.5 micrometers and smaller. How small is 2.5 micrometers? Think about a single hair from your head. The average human hair is about 70 micrometers in diameter -- making it 30 times larger than the largest fine particle. These particles come in many sizes and shapes and can be made up of hundreds of different chemicals. Some particles, known as primary particles, are emitted directly from a source, such as construction sites, unpaved roads, fields, smokestacks or fires. Others form in complicated reactions in the atmosphere of chemicals such as sulfur dioxides and nitrogen oxides that are emitted from power plants, industries and automobiles. These particles, known as secondary particles, make up most of the fine particle pollution in the country.

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Interpreting the AQI

Air Quality Index

Each NAAQS pollutant has a separate AQI scale, with an AQI rating of 100 corresponding to the concentration of the Federal Standard for that pollutant. Additional information about the AQI and how it can be used is available from the EPA's AirNow web site.

Place your mouse pointer over the scale displayed above to view information about the Air Quality Index, and each of the rating levels.

The actual index calculation is different for each parameter measured and is specified by the EPA. The following table shows the various breakpoints used in calculating the AQI.

AQI Breakpoint Definitions
AQI Range 1hr Ozone
in ppm
8hr Ozone
in ppm
8hr Carbon Monoxide
in ppm
1hr Sulfur Dioxide
in ppm
24hr Sulfur Dioxide
in ppm
1hr Nitrogen Dioxide
in ppm
24hr PM-10
in µg/m³ (25° C)
24hr PM-2.5
in µg/m³ LC
24hr PM-2.5
in µg/m³ LC
0 - 50 Not Defined 0 - 0.054 0 - 4.4 0 - 0.035 Not Defined 0 - 0.053 0 - 54 0 - 12.0 0 - 12.0
51 - 100 Not Defined 0.055 - 0.070 4.5 - 9.4 0.036 - 0.075 Not Defined 0.054 - 0.1 55 - 154 12.1 - 35.4 12.1 - 35.4
101 - 150 0.125 - 0.164 0.071 - 0.085 9.5 - 12.4 0.076 - 0.185 Not Defined 0.101 - 0.36 155 - 254 35.5 - 55.4 35.5 - 55.4
151 - 200 0.165 - 0.204 0.086 - 0.105 12.5 - 15.4 0.186 - 0.304 Not Defined 0.361 - 0.649 255 - 354 55.5 - 150.4 55.5 - 150.4
201 - 300 0.205 - 0.404 0.106 - 0.200 15.5 - 30.4 Not Defined 0.305 - 0.604 0.65 - 1.249 355 - 424 150.5 - 250.4 150.5 - 250.4
301 - 400 0.405 - 0.504 Not Defined 30.5 - 40.4 Not Defined 0.605 - 0.804 1.25 - 1.649 425 - 504 250.5 - 350.4 250.5 - 350.4
401 - 500 0.505 - 0.604 Not Defined 40.5 - 50.4 Not Defined 0.805 - 1.004 1.65 - 2.049 505 - 604 350.5 - 500.4 350.5 - 500.4
500+ Not Defined Not Defined Not Defined Not Defined Not Defined Not Defined Not Defined Not Defined Not Defined

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PLEASE NOTE: This data has not been verified by the Virginia DEQ and may change. This is the most current data, but it is not official until it has been certified by our technical staff. Data is collected from Virginia DEQ ambient monitoring sites and may include data collected by other outside agencies. This data is updated hourly. All times shown are in local standard time unless otherwise indicated.