Frequently Asked Questions

  1. I live on the border between two (or more) forecast regions. When they have different forecasts, which should I follow?
  2. Why was Maine broken into the eight Air Quality Forecasting regions?
  3. Can I be alerted when Air Quality is forecast to be poor?
  4. Why does MEDEP issue air quality forecasts year-round?
  5. In a recent forecast discussion you mentioned a 'dirty air mass'. What do you mean and what causes an air mass to be dirty?
  6. The Air Quality Forecast for a pollutant is different than what the current data shows. Why is that?
  7. What is the difference between particle pollution and coarse particles mentioned in your winter forecast discussions?
  8. Does ozone behave differently with height?
  9. I can see pollution in the air, is it ozone?
  10. MEDEP and EPA warn about Ozone yet it has been touted as a great indoor air cleaner. Why is that?
  11. Does MEDEP have any information about winds in Maine?

1. I live on the border between two (or more) forecast regions. When they have different forecasts, which should I follow?

In the atmosphere political boundaries do not exist and neither do forecast regional boundaries. The forecast regional boundaries were positioned based on years of monitoring information and our best judgement. It is a good idea to view the borders as a transition between regions rather than a sharp difference. If you are sensitive to the pollutant in question and live or expect to be along the border between two differing forecasts assume the higher forecast category from the regions will prevail in your area. This will enable you to take appropriate precautions to safeguard your health. We strive to give you the information you need to protect your health. While the new forecasting regions allow us to issue a forecast that more accurately portrays what we believe will happen, there are more border areas.


2. Why was Maine broken into the eight Air Quality Forecasting regions?

For years we had three forecast regions: Coastal, Interior and Northern. As we learned more about how Ozone and Particle Pollution behaved in Maine it became apparent that the three regions were not adequate. They were fairly good for Ozone, but not good at all for Particle Pollution. So we refined and subdivided the former regions using the monitoring data for both pollutants and our best judgement. We created seven major forecast regions which display in the table as well as on the forecast maps. This gives us more flexibility in issuing a graphical forecast and better descriptive and consistent regional terms to use in the text and hot line messages.

Of course, it also pushes us to do better and refine our forecasting knowledge. Who knows, in the years to come we may realize these seven major regions need to be revised, especially as we learn more about how pollution behaves in our northern areas.

In addition to the seven major forecast regions, we've added a region called 'High Elevation'. This region includes the ozone monitor on Cadillac Mountain in Acadia National Park. The High Elevation forecast region only displays in the table because it would have been a tiny dot on the map which would have been hard to display properly.


3. Can I be alerted when Air Quality is forecast to be poor?

Yes, you can. Maine DEP uses both EnviroFlash and Twitter to get the word out. 

EPA created EnviroFlash an automated zip-code based air quality alert email notification system. EnviroFlash covers the entire state of Maine and allows the subscriber to decide at which Air Quality Index (AQI) level to receive email notification.

DEP's Air Quality Meteorologists submit the forecast to EPA's AIRNOW system every day of the year. EnviroFlash will review the forecast in AIRNOW at 4:00 each afternoon and when tomorrow's forecast in your location matches the criteria you set up an email will be sent to you. Let EnviroFlash help you 'Keep an eye on the AQI'. 

Go to: http://www.maine.gov/dep/air/ozone/enviroflash.html for more information about EnviroFlash and how to subscribe then click on the map to initialize the subscription process for EnviroFlash!

Four Twitter accounts have been set up for different parts of the state. EnviroFlash automatically generates tweets for these accounts and the air quality meteorologists can issue tweets manually when necessary. Find out how to follow the air quality forecast for your area by going to: http://www.maine.gov/dep/air/aqforecast/twitter.html

 


4. Why does MEDEP issue air quality forecasts year-round?

MEDEP Air Quality Meteorologists issue Air Quality Forecasts every day of the year because air quality is not just seasonal. Ozone is a photochemical pollutant which means it requires strong sunlight. That is why ozone levels are only a problem in Maine during the warmer months. However, particle pollution levels can climb at any time of the year in Maine. During the summer months particle pollution levels can rise due to regional events. During the winter particle pollution levels can climb due to a combination of factors including winter heating needs.


5. In a recent forecast discussion you mentioned a 'dirty air mass'. What do you mean and what causes an air mass to be dirty?

A dirty air mass is caused by a slow moving weather system trapping and pushing air pollution across the country. There is no specific source or region contributing to the pollution. All emissions from highly populated areas, industrial sources, mobile sources, smoke from wild fires and more get trapped in the air mass. The slower it moves the dirtier it is by the time it reaches New England. The only relief for Maine comes when a front finally pushes that air out to sea. The strength, direction of movement and speed of a front determines which areas of Maine will clean out first. A strong and/or fast moving front will clean Maine out quickly while a slow moving and/or weak front will take longer to clean out the state.


6. The Air Quality Forecast for a pollutant is different than what the current data shows. Why is that?

You are viewing the data during a small part of the day, yet values will be higher during another part of the day and that data is what the forecast is based on.

This is often the case with Ozone which is a photochemical pollutant and peaks during the afternoon hours (from April through September). Both morning and evening values are likely to be low. Ozone forecasts are for the highest 8-hour period of the day.

For Particle Pollution values, the running 24-hour average for several hours may be Moderate yet the block 24-hour average from midnight to midnight for that day ends up being Good. It is this block, midnight to midnight, average for which we issue the forecast. When we believe that particle levels will build in late one day and clear out early the next we will mention this in the forecast details on the Air Quality Forecasting web page.

The Air Quality Trends pages have hourly and other trends for ozone and particle pollution.

Finally, although we make every effort to forecast as accurately as possible, it is still an inexact science and, just like the weather forecasts upon which we base our Air Quality Forecasts, we may be wrong. Sometimes we know the values will end up near the break point between categories. In those cases we carefully weigh the various factors contributing to the pollution levels and make a decision based on experience and the most likely weather conditions expected. Sometimes we believe it will be such a close call that we err on the side of protecting the public and issue the forecast for the higher of the two categories. Unlike weather forecasters who are able to give a range of temperatures or weather conditions, we issue forecasts for a specific category and a very small change in pollution levels will 'make' or 'break' the forecast.


7. What is the difference between particle pollution and coarse particles mentioned in your winter forecast discussions?

Particle pollution is a term that refers to very small particles that can be carried deep into the lungs and even enter the bloodstream. These particles are less than 2.5 micrometers in diameter and so small that they can remain airborne for a relatively long time. Thus, particle pollution is often referred to as PM2.5 where 'PM' stands for particulate matter.

Particles larger than 2.5 micrometers in diameter can be filtered by the breathing passages and also settle out of the atmosphere more readily. These particles are now referred to as coarse particles and most often the size is between 2.5 to 10 micrometers. Thus coarse particles may also be referred to as PM10 or PM2.5to10.


8. Does ozone behave differently with height?

Yes. We've studied years of ozone data from the Cadillac Mountain monitor. We've learned that:

  • Ozone levels do not drop as readily after the sun sets at high elevation sites such as Cadillac. In fact, Cadillac Mountain's ozone levels frequently peak after 10 PM while low elevation ozone levels are dropping.
  • Cadillac Mountain's height places the monitor at an elevation to monitor ozone transport aloft. At this level ozone is more stable and doesn't break down as readily. At this level transport winds have reduced friction from the surface so ozone aloft can travel faster and further than surface ozone.
  • Additionally, Cadillac Mountain is geograhically located downwind of major metropolitan areas and large emission sources that are outside of the state of Maine. Ozone is formed by chemical reactions in the atmosphere in the presence of sunlight. So the pollution emitted in one area can be lofted and transported to another with ozone forming as the air mass is transported.

For information on how ozone differs from one part of Maine to another, from one year to another and during the day please return to the Air Quality Forecast home page and use the contact us function at the bottom of that page.


9. I can see pollution in the air, is it ozone?

Ozone is often described as a colorless pollutant. In fact, it is a pale blue. So for all intents and purposes you cannot see ozone. You may be looking at fog or mist. If you are seeing pollution in the air, it is particles. Particle pollution affects the lungs and so much more. Check out the health messages by going to: http://www.maine.gov/dep/air/ozone/airqualityindexandhealth.html  .


10. MEDEP and EPA warn about Ozone yet it has been touted as a great indoor air cleaner. Why is that?

Ozone in the lower atmosphere is a pollutant. There is no doubt about that. While ozone is able to clean the air, one needs to monitor its use very closely to avoid unhealthy levels. This is a very complicated process and not easily accomplished without sophisticated monitoring equipment and continuous vigilance.

The Maine Indoor Air Quality Council covers general indoor air quality issues at: http://www.miaqc.org/

The U.S EPA deals with indoor air in general at: http://www.epa.gov/iaq/index.html and ozone generators/air purifiers more specifically at: http://www.epa.gov/iaq/pubs/ozonegen.html
California Air Resources Board has issued a report assessing the health impacts of indoor air pollution. Air 'purifiers' that emit ozone were included in their list of indoor air pollution sources which contribute to asthma, respiratory disease and more. For more information go to: http://www.arb.ca.gov/research/indoor/aircleaners.htm


11. Does MEDEP have any information about winds in Maine?

Yes, we do. MEDEP Air Quality Meteorologists have provided access to images (called wind roses) of wind data for sites around the state at: http://www.maine.gov/dep/air/meteorology/Windrosehome.html If you have never seen a wind rose there is a web page of information about how to read a wind rose and understand what it means. It is important to realize that a wind rose is specific to that location and may not be an accurate representation of winds even a few miles away depending on several factors including topography.