North Shore AIR

Contribution by Source

HOW DOES EACH OF THESE SOURCES CONTRIBUTE TO OUR AIR POLLUTION?

Essex County - Source Contribution of Criteria Air Pollutants

To determine the contribution by the different source categories, first the contribution to Criteria Air Pollutants was reviewed.  This data was available from the EPA 1999 NEI.

Since this includes the contribution of VOCs, most of the HAPs are also included as a subset of VOCs.  To double check this assumption, HAP estimates from EPA's  1999 NATA system were added to the total criteria pollutants yet the ratio of distribution by source type was not affected.  Thus Mobile Sources are certainly the largest contributer to air pollution in Essex County at 71% of the total contribution, while Area Sources at 14%, and Major Sources at 15% contribute significantly smaller portions of the total air emissions.

Further evaluation of the specific Criteria Air Pollutants helps further explain this distribution.

 This detailed review, reveals that in Essex County:

• Mobile Sources contribute the largest emissions for 5 of the specific pollutants/pollutant groups (including HAPs),
• Point Sources contribute the most Sulfur Dioxide, and
• Area Sources contribute the most VOCs.

The next step was to understand source contribution at the 3 target community level.   

Target Communities - Source Contribution of HAPs

At the target community level - Criteria Air Pollutant estimates for all sources was not readily available from EPA as it was at the county level.  Two alternative data sets were used to further understand source contribution at the community level.  However, only the EPA data of HAPs (a subset of the total air pollutants) could be used to compare contribution from the different sources at the town level.

• EPA's 1999 NATA data provides detailed estimates at the census tract level, and therefore the town level, for the contribution by sources of Hazardous Air Pollutants (HAPs).  This data analysis is discussed below.
• MADEP's Air Source Registration data (from 2003) provides Point/Major Source contribution of Criteria Air Pollutants and total HAPs.  Since this data was only from one source category- this review can be found in our detailed review of Major Sources.

Contribution by Source to HAP Emissions

In the communities of Salem, Beverly and Marblehead, background and mobile sources are the greatest sources of Hazardous air pollutants (HAPs).  Mobile sources account for the most air pollution at 190 tons per year. This is a combination of on-road sources which account for 133 tons, and off-road sources which account for 54 tons. Background sources are those that the wind carries in from other areas or are a result of historic use that remains persistent in the environment, and cannot be regulated on the local level yet they account for a significant percentage (33%) of the total air pollution that is estimated in the area. Area sources are the 3^rd largest category, and the Major point sources account for the lowest amount of this subset of air toxins.

Emissions by Source Type HAPS Only:

In general, each town has a similar distribution, or percentage per type of source.