Halethorpe Weather-Watch  

The Air Quality Index (AQI) is divided into six categories. Each category corresponds to a different level of health concern. Each category also has a specific color. The colors makes it easy for people to quickly determine whether air quality is reaching unhealthy levels in their communities.
The Clean Air Act requires the EPA to set National Ambient Air Quality Standards (NAAQS) for six common air pollutants (also known as "criteria air pollutants"). Ground-level Ozone (O₃), Carbon Monoxide (CO), Sulfur Dioxide (SO₂), Lead (Pb), Nitrogen Dioxide (NO₂), and Particulate Matter (PM).
Particulate Matter, abbreviated as PM (also called particle pollution): 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:
PM10 : inhalable particles, with diameters that are generally 10 micrometers and smaller; and
PM2.5 : fine inhalable particles, with diameters that are generally 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 are emitted directly from a source, such as construction sites, unpaved roads, fields, smokestacks or fires. Most particles form in the atmosphere as a result of complex reactions of chemicals such as sulfur dioxide and nitrogen oxides, which are pollutants emitted from power plants, industries and automobiles.¹

NowCast reading shows the current air quality. It is calculated using the data for the current hour as well as multiple hours of past data. It uses a heavier averaging weight for recent hours of data and data that is changing rapidly. The NowCast reading is used in lieu of a 24-hour average, to give you a more useful indication of the danger of the air quality over that period. 2 NowCast current readings of Air Quality Index (US EPA), updated every 10 minutes.2  This index is based solely on particulate matter. Information on NowCast AQI calculation can be found on the AirNow Forum. Real-time current readings of particular matter (PM1, PM2.5, and PM10), updated every 10 minutes. 2 Last 60 minute mean, minimum, and maximum concentration readings, updated every 10 minutes.5

Why Should We Worry About PM2.5?
Exposure to PM2.5 has multiple short term and long term health impacts. Short term include irritation in the eyes, nose and throat, coughing, sneezing and shortness of breath. A prolonged exposure to PM2.5 can cause permanent respiratory problems such as asthma, chronic bronchitis and heart disease.
While PM2.5 impacts everyone, people with breathing and heart problems, children and the elderly are most sensitive to it. Due to the omnipresence of particulate matter, ambient particulate matter has proved to be a killer more potent than alcohol and diabetes.³

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