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Maine's Air Quality Forecast, Ozone and Particle Pollution

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Air Quality Forecast Availability
Ozone
Particle Pollution
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Air Quality Forecast Availability

Map of Maine air quality forecast regions — Forecast map
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Maine DEP air quality meteorologists issue Air Quality Forecasts year-round. These forecasts capture what is expected to be the worst in that region.
Ground-level ozone concentrations are higher during the summer months. Particle pollution levels tend to be higher during the summer and winter and lower during the spring and fall.
Since many factors impact pollution levels including terrain and geography, please see ozone and particle pollution specifics below for information to help interpret the forecast for your location.
Maine DEP's Air Quality Forecast website is the best place to check the forecast. When it is appropriate, air quality meteorologists will include more information about the forecast and current air quality.
The forecast is made available to the public daily in the following ways:

24-hour toll free Air Quality hotline: 1-800-223-1196
Online on this site - daily forecasts
EnviroFlash -- Email and text message alert system established by Environmental Protection Agency (EPA) in cooperation with Maine DEP.
AirNow's mobile app -- EPA's AirNow app has a sleek new look and improved functionality! Download the updated app for free on the Apple App Store or the Google Play Store.
Local media

When poor air quality is expected, Maine DEP also submits Air Quality Alerts to:

The Citizen Alert System on the State of Maine home page (Maine.gov)
The National Weather Service's Maine Offices

As more people rely on mobile apps and want localized forecasts and data, many options are becoming available. They are likely to use a computer model to approximate a forecast, or current values at specific locations. They may use a different index to present the forecast or data than EPA's Air Quality Index. The EPA is working with some of these other sources to try to reduce confusion and present information in similar ways for the benefit of the public.

Ozone

What is it?

Ozone is an extremely reactive virtually colorless gas comprised of three atoms of oxygen.
In the upper levels of the atmosphere, it shields the earth from the sun's harmful ultraviolet rays.
However, ozone close to the ground is a harmful pollutant.
That is why we say, “Good up high, bad nearby.”

Where does it come from?

Ozone is formed through a complex chemical reaction between volatile organic compounds (VOCs) and nitrogen oxides (NOx) in the presence of sunlight. Therefore, it is called a photochemical pollutant.
Sources of manmade VOCs and NOx include:

automobiles, trucks and buses
gasoline storage and transfer
large combustion and industry sources such as utilities
industrial use of solvents and degreasing agents
consumer products such as paints and cleaners
off-road engines such as aircraft, locomotives, boats, construction equipment and lawn and garden equipment.

VOCs are also produced naturally by certain types of vegetation.
The EPA has more information about ground-level ozone.

How does it behave in Maine?

By season – since ozone needs the sun to form from NOx, VOC's and other precursors in the air, it is most abundant at the surface when the sun is higher in the sky and the days are longer. Maine's official Ozone monitoring season is April 1st through September 30th. Levels of ozone begin to rise in late February and early March. Monitoring staff try to get as many of our seasonal monitors running prior to April 1st depending on location accessibility. Additionally, some seasonal ozone monitors continue running into October.
By height – Ozone levels do not drop as readily after the sun sets at high elevation sites such as Cadillac Mountain in Acadia National Park. In fact, Cadillac Mountain's ozone levels frequently peak after 10 PM while at lower elevations, ozone levels are dropping. At higher elevations, winds travel faster than at ground-level. Therefore, ozone aloft can travel faster and further than ground-level ozone. In the morning, when the sun begins mixing the air, ozone from aloft can be brought down to lower elevations.
By temperature – Ozone is a very unstable gas. It breaks down readily. Warmer temperatures reduce this instability which helps ozone to reach higher levels during the warmer months. However, just because it is hot does not mean that ozone levels will be high in Maine. Maine's ozone levels are the result of how much ozone and its precursors are transported to the state. If the wind comes from areas with low ozone levels, ozone will be lower in Maine. As a result, Maine has had some very hot summers with very few days when ozone reaches the Unhealthy for Sensitive Groups range on the Air Quality Index.
By geography and terrain – Warmer months' ozone varies across the state. Sunshine heats land faster and more effectively than water. The cooler water in the Gulf of Maine causes the air to concentrate pollutants in a shallow layer just above the surface of the water. Additionally, this same impact changes the wind direction, turning the winds toward the Maine coast. As the day progresses, ozone and its precursors continue to move eastward along the Maine coast. This is one of the factors that contributes to higher ozone levels along Maine's coast. After the leaves are unfurled on the trees, the vegetation removes ozone from the air as it pushes inland. Even one town inland from the coast, ozone levels will be lower than right along the coast. One exception is that river valleys can channel air moving inland from the coast, concentrating ozone levels within the valley.
Typical ozone event progression – Ozone and its precursors are transported from the New York metropolitan region across Connecticut and Massachusetts into the Gulf of Maine. Along the Maine coast, the timing of the ozone peak progresses as the air mass is transported from west to east. Near the New Hampshire border, the peak is often midafternoon. Near Mount Desert and beyond, the peak is during the early to late evening hours.

Particle Pollution

What is it?

Particle pollution is a term for pollution that includes both solid particles (dust, dirt, soot, smoke, etc.) and liquid droplets found in air. Particles come in a wide range of sizes. Particles less than 10 micrometers in diameter can be inhaled and accumulate in the respiratory system. Particles less than 2.5 micrometers are called fine particles. This is the size range included in the particle pollution forecast. The EPA as more information about particle pollution.

Where does it come from?

Some particles are emitted directly into the air. They come from a variety of sources such as cars, trucks, buses, locomotives, ships, factories, construction sites, tilled fields, unpaved roads, stone crushing, and the burning of wood.

Other particles form in the air from chemical processes. They are indirectly formed when gases from fuel combustion react with sunlight and water vapor.