This map illustrates near real-time concentration of ammonia (NH3), fine particulate matter (PM-2.5) and coarse particulate matter (PM-10) measured at the two Lower Eastern Shore (LES) monitoring stations. The Pocomoke City station is located in an area expected to be impacted by proximity to a high density of poultry houses, while the Princess Anne station is located in an area where there are very few poultry houses nearby. For comparison purposes, near real-time concentrations of NH3 and PM-2.5 measured at the Oldtown station, in downtown Baltimore City, and the Horn Point Lab, near Cambridge, are also presented on this map. PM-10 is not measured continuously at either of these locations.
National Ambient Air Quality Standards (NAAQS) have been established for both PM-2.5 and PM-10. Concentrations are displayed for the most current hour and the 11 previous hours, and are expressed in micrograms per cubic meter (ug/m3) and are also represented by their respective Air Quality Index color codes (link to AQI explanation).
No NAAQS have been established for ammonia; however, risk-based residential and worker air concentration screening levels have been issued by various federal and state agencies. Among the available exposure levels that exist, the three that are shown in the chart below reflect those that best fit the objective of this project – to provide data on residential air quality in the vicinity of poultry operations. The first is EPA’s residential lifetime exposure concentration, which assumes an exposure concentration reflective of a residential setting, where an individual would be exposed 24 hours a day, 350 days a year, for 30-years.
The second and third values in the chart are MDE’s air toxics screening levels. These screening levels are used during the permitting of point sources of pollution to determine whether the emissions from a point source would pose a threat to public health. The screening levels are conservative in nature, as they represent the worker protection exposure levels developed by the American Conference of Governmental Industrial Hygienists divided by a safety factor of 100.
The ambient air ammonia screening concentrations presented in the table below may be compared to results of the real time concentrations of ammonia detailed on the accompanying webpage map. The concentrations reported on the map are displayed for the most current hour and the 11 previous hours. All results on the map and webpage are reported in parts per billion by volume (ppbv).
In terms of odors, there is no universally accepted concentration at which ammonia can be detected. An odor threshold for ammonia has, however, been documented in different studies to be as low as .04 ppm (40 ppb), and it is noted here that sensitivity to odors can vary among individuals. This threshold is below the levels shown above that are being used to determine impacts to public health, which means that an odor can be detected before the concentration reaches a level where public health is being impacted.
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