FREEHOLD, NEW JERSEY -- The need for accurate methods of quantifying industrial-source emission rates of methane and other greenhouse gases (GHGs), as well as other air pollutants, has never been greater, both domestically and abroad. Today, Minnich and Scotto, Inc. (www.msiair.net) announces the availability of e-Calc© – an emissions-calculation software package to yield air pollutant emission rates from a wide range of sources, in real time, based on the area-source technique using AERMOD.
The Windows-based e-Calc software “back-calculates” precise 15-minute-averaged emission-rate snapshots (mass per time) from virtually any ground-level source, such as an oil and gas production well-pad component, a landfill, a wastewater lagoon or pond, a hazardous waste site cleanup, or a transportation-related accident. Originally created to help municipal solid waste landfill owners comply with mandated methane emissions reporting and permitting requirements, e-Calc is designed for easy use with any open-path spectrometer. It can also accommodate point-type monitor data, as long as the measured concentrations along a downwind path are spatially averaged.
The area-source technique, upon which e-Calc is based, was developed by the U.S. EPA Environmental Response Team in the early 1990s for deriving emission factors during pilot-scale Superfund remediations. It is intended primarily for use with optical remote sensing (ORS) – either FTIR, UV, or TDL open-path spectroscopy – in which a path-integrated concentration is generated in the cross-plume dimension, i.e., a “whole-plume” approach.
Parameterization of plume transport and dispersion within the microscale region between the source and the downwind measurement path, via sophisticated surface-based meteorological monitoring, obviates the need for measuring contaminant concentrations or meteorological data in the vertical dimension (i.e., the extent of the pollutant’s lateral and vertical dispersion is inherently accounted for, taking full advantage of the principle of conservation of mass).
Recently, Minnich and Scotto, working with Kassay Field Services, Inc., www.kassay.com, successfully performed a 5-week field study under contract to the South Coast Air Quality Management District (SCAQMD), in which e-Calc was employed using open-path FTIR spectroscopy to measure emission rates of speciated hydrocarbons downwind of nearly 40 gas stations, active oil wells, and cattle farms.
The area-source technique involves the 15-minute-averaged cross-plume measurement of source attribution (i.e., a “monitoring event”), and the subsequent back-calculation of a coincident emission rate based on Gaussian dispersion relationships inherent in most air dispersion models; in this case, the model is AERMOD, U.S. EPA’s Guideline air dispersion model for regulatory application. Sometimes referred to as “inverse modeling,” this back-calculation can be thought of as the 15-minute-averaged “snapshot” emission rate required to yield the measured downwind path-integrated concentration under the atmospheric conditions influencing the source during that precise 15-minute period.
E-Calc computes wind-speed profiles and dispersion coefficients based on surface characteristics, solar insolation, and statistical data treatments such as the standard deviations of the vertical wind speed and horizontal wind direction.
E-Calc employs the U.S. EPA regulatory version of AERMOD in order to maintain the model’s legal Guideline status. As such, all e-Calc results are technically defensible and legally admissible in a court of law.
For each 15-minute monitoring event, the generation of e-Calc input files requires meteorological data, together with emissions-characterization and monitoring configuration data. Most input data are directly measured and entered into the software program automatically. Pre-identified source locations together with beam-path coordinates are manually entered into simple data input screens.
The area-source technique calculates an emission rate for a given pollutant in accordance with the following equation:
C / Q = CU / QU
C = measured path-integrated concentration (attribution) (mg/m2);
Q = actual emission rate (mg/s);
CU = predicted unity-based path-integrated concentration along the measurement path (mg/m2); and
QU = unity-based emission rate (mg/s).
This equation describes the inherent relationship between: (a) the unity-based dispersion modeling; and (b) the actual emission rate and downwind measurements. The cornerstone of the area-source technique, this ratio states that the measured path-integrated concentration is to the actual emission rate as the unity-based path-integrated (modeled) concentration is to its unity-based emission rate. The only unknown term in this equation is the actual emission rate (Q).
The spectrometer generates the measured path-integrated concentration (C). AERMOD is configured to yield a predicted concentration for each meter along the beam path. These predictions are summed to derive the predicted unity-based path-integrated concentration (CU).
Assignment of the unity-based emission rate (QU) is straightforward (i.e., simply set to 1 mg/s), unless the source includes multiple emission “subareas” of varying magnitude. In such a case, multiples of unity are assigned to each subarea based on either determination of relative source strengths or best professional judgment.
The e-Calc analysis screen is utilized for entry of event-specific meteorological data leading to emissions calculations via AERMOD, as well as the subsequent generation of a hard-copy report for each monitoring event. An example (actual) e-Calc analysis screen is shown below for a single monitoring event.
E-CALC ANALYSIS SCREEN
Finally, e-Calc can be used to easily assess community impacts. An e-Calc-derived source term can be directly input to AERMOD for prediction – via forward modeling – of downwind community impacts across any specified receptor field.
For further information about e-Calc, and how it can be applied to meet your specific needs, please contact Tim Minnich at email@example.com, or call (732) 409-9900.