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New Issues in Air Monitoring


Sulfur Dioxide (SO2 )

EPA air quality standards have developed a new National Ambient Air Quality Standard (NAAQS) for Sulfur Dioxide concentration averaged over a one-hour period.  Historically,  attainment status has been assessed using existing monitors located across the nation.  However,  due to the large number of affected facilities and a lack of adequate spatial coverage of the existing monitoring network,  EPA has approved using a combination of both dispersion modeling and ambient monitors  to demonstrate compliance.  Although Dispersion Modeling is less time consuming and is less expensive compared to ambient monitoring,  the conservative approach used in modeling may provide unrealistically higher predicted concentrations compared to actual measurements from an ambient monitoring study.  If you suspect this to be the case, it may be in your interest to initiate a monitoring study.  Shell Engineering and Associates can provide ambient monitoring services for your facility.

Particulate Matter

For most pollutants, if the modeled emissions are below a Significant Monitoring Concentration (SMC) level, preconstruction monitoring can be exempted.  However, PM2.5 (particulate matter < 2.5 microns) must be analyzed a little differently in this regard.  As a result of a D.C. Circuit Court decision in January 2013, in which the PM2.5 SMC was vacated, all PM2.5 air quality analyses must include monitoring from a “representative source”.  If the state has a monitoring network for PM2.5, a nearby monitor may be considered representative.  If not, preconstruction monitoring will be required.   In addition,  due to EPA setting a low National Ambient Air Quality Standard for PM2.5, it is very important to obtain an accurate background concentration for PM2.5.  An overstatement of background concentrations may require excessive controls be applied to new construction activities. Shell Engineering can perform a review of nearby PM2.5 monitoring stations to determine if they are representative for use in your permit application.   In addition, if PM2.5 monitoring is required,  one year of monitoring is typically required before a permit to construct will be issued.   Shell Engineering and Associates, Inc. can assist you with your particulate monitoring requirements.

Nitrogen Dioxide (NO2)

EPA developed a new National Ambient Air Quality Standard (NAAQS) for Nitrogen Dioxide concentration averaged over a one-hour period.  Modeled values for NO2 may be predicted to be high due to a large number of sources emitting NO2, and due to the difficulty of accounting for the chemistry involved between Nitrogen Oxide, Ozone, and Nitrogen Dioxide.  In some cases it may be deemed to be more appropriate to monitor Nitrogen Dioxide directly in the ambient air to show compliance with the new NAAQS rule, or for determining a background concentration for use in subsequent dispersion modeling.  Shell Engineering and Associates, Inc can assist you with your Nitrogen Dioxide monitoring requirements.

If you’d like to learn more about our air monitoring services contact us today.