Air Quality Facts

To learn more about air quality measurements, Air Quality Facts are provided to highlight ground-level ozone and particle pollution trends and inform citizens of revised National Ambient Air Quality Standards (NAAQS) and Air Quality Index (AQI). In addition t​o the common topics below, more air quality questions may be answered at AirNow FAQs.

Ozone at High Elevation 

Mountaintop Ozone

Ozone pollution has a distinct behavior at high elevation. For example, ozone measured near sea level often exhibits a daily trend with maximum values occurring in the afternoon (see Daily Climatology for Ozone below) whereas elevated areas may see a consistent level of ozone from morning to night. One moutaintop air monitoring site operated by the Department of the Environment is known to measure regional pollution transport from the west as a result of its elevation and distance from air pollution sources. Download the fact sheet to learn more.

Extent of the Ozone Pollution Plume

Ozone Plume Extent

During a typical air pollution episode, the ozone pollution plume is found along the I-95 corridor, from northern Virginia through Maryland, and can extend up to Boston, Massachusetts. A plume refers to a polluted airmass. Within the plume, high ozone concentrations are found in suburban and rural locations downwind from city centers, rather than the city itself. Download the fact sheet to learn more.

Daily Climatology for Ozone and Particle Pollution (PM2.5)

Diurnal Climatology

Ozone and particle pollution observe unique daily, or diurnal, trends. Ozone has a strong diurnal pattern with highest concentrations occurring between noon and early evening while particle pollution peaks during the morning and late afternoon hours. Download the fact sheets to learn more.

Seasonal Climatology for Ozone and Particle Pollution (PM2.5)

Seasonal Climatology

Ozone and particle pollution exhibit distinctive seasonal patterns. Ozone pollution typically reaches a maximum from June through August while particle pollution reaches two maximums during the months of February and July-August. Download the fact sheets to learn more.

2012 Revised Air Quality Index for Particle Pollution (PM2.5)

Revised PM2.5 AQI

On December 14, 2012, the EPA revised the Air Quality Index (AQI) for daily 24-hour average fine particle pollution. This revision was part of the strengthening of the annual fine particle pollution National Ambient Air Quality Standard (NAAQS) (www.epa.gov/pm/actions.html#dec12). Only the Good and the Moderate categories were affected by this change to the AQI. The upper range of the Good AQI was revised to the level of the annual fine particle pollution NAAQS of 12.0 ug/m3. The revised AQI, effective March 18, 2013, replaced the AQI that the Maryland Department of the Environment has used since 2009. Download the fact sheet to learn more.

2008 Ozone Standard and Revised Air Quality Index

2008 Ozone Standard

On March 12, 2008, the EPA strengthened the National Ambient Air Quality Standards (NAAQS) for ground-level ozone from 84 ppb to 75 ppb (http://www.epa.gov/air/ozonepollution/actions.html). The new standard was adopted and reflected that over 1,700 scientific studies linked adverse health effects at the level of the old standard or below. The color-coded Air Quality Index (AQI) for 8-hour ozone (which is used for air quality reporting and forecasting) was also revised. The new standard and the revised AQI will help improve the protection of public health and the protection of sensitive trees and plants. Four fact sheets (prepared by forecast region) are provided to help you understand how the new ozone standard will affect you and how you can make conscious simple everyday decisions that will help improve the quality of the air we breathe as well as the environment.

Generally, the number of unhealthy air days are expected to double for the Baltimore-Washington Metro area and quadruple in rural areas (Western Maryland and Eastern Shore) based on ozone data from 2003-2007. To learn more about the expected changes in your region, download the following fact sheets:

2015 Ozone Standard and Revised Air Quality Index

2015 Ozone Standard  

On October 1, 2015, the EPA strengthened the National Ambient Air Quality Standards (NAAQS) for ground-level ozone from 75 ppb to 70 ppb (http://www3.epa.gov/ozonepollution/actions.html). The new standard was adopted based on extensive scientific evidence about ozone’s effects on public health and welfare. The updated standards will improve public health protection, particularly for at-risk groups including children, older adults, people of all ages who have lung diseases such as asthma, and people who are active outdoors, especially outdoor workers. They also will improve the health of trees, plants and ecosystems. The color-coded Air Quality Index (AQI) for 8-hour ozone (which is used for air quality reporting and forecasting) was also revised. Four fact sheets (prepared by forecast region) are provided to help you understand how the new ozone standard will affect the number of poor ozone air days you experience.  Simple, everyday decisions can help improve the quality of the air we breathe as well as the environment on days when ozone is expected to be high.

Generally, the number of unhealthy air days is expected to increase by about 50% for the Baltimore-Washington Metro area.  That means about 15 poor air days (USG and greater) when formerly there was 10.  In rural areas (Western Maryland and Eastern Shore) the number of days are expected to double based on ozone data from 2005-2015.

To learn more about the expected changes in your region, download the following fact sheets:

Contact Information

For more information about the Air Quality Monitoring Program please contact Janice Lafon at (410) 537-3280 or email janice.lafon@maryland.gov.
​​​