Guidance Document. Plume Dispersion Modelling GD-PPD Guideline for Plume Dispersion Modelling

Transcription

1 Government of Newfoundland and Labrador Department of Environment & Conservation Pollution Prevention Division (Environment) Guidance Document Title: Guideline for Plume Dispersion Modelling Prepared By: Barrie Lawrence, Environmental Scientist Issue Date: June 10, st Revision: November 20, 2006 Approved By: Derrick Maddocks, Director Plume Dispersion Modelling GD-PPD-019.1

2 Table of Contents SUBJECT... 3 OBJECTIVE... 3 BACKGROUND... 3 DEFINITIONS APPROVED MODELS CALPUFF MODELLING SYSTEM - OVERVIEW AERMOD MODELLING SYSTEM - OVERVIEW US EPA SCREEN3 MODEL - OVERVIEW SCREEN3 MODEL - SPECIAL CIRCUMSTANCES AERMOD MODELLING SYSTEM - SPECIAL CIRCUMSTANCES POLLUTANTS TO BE MODELLED AVERAGING PERIODS TO BE MODELLED NO X VS NO NO X FORMATION AND PRIMARY CONTROL NO X FROM INDUSTRIAL SOURCES BASIC NO x CHEMISTRY IN THE ATMOSPHERE NO DISPERSION MODELLING INTERPRETATION GUIDANCE AERMOD MODELLING SYSTEM - MODELLING PROVISIONS AERMET AERMAP AERMOD CALPUFF MODELLING SYSTEM - MODELLING PROVISIONS CALMET CALPUFF CALPOST REPORTING BPIP REFERENCES

3 SUBJECT The plume dispersion modelling methods approved by the department for the purpose of determining compliance with the ambient air quality standards in the Air Pollution Control Regulations. OBJECTIVE To define the terms and conditions that proponents are to follow when conducting an air quality assessment of a facility in Newfoundland and Labrador. In so doing, the department ensures that the quality of all results obtained and submitted to the department are complete and consistent across all facilities and employ the latest advances in modelling technology. BACKGROUND Under the Air Pollution Control Regulations, the ambient air quality standards are defined for a series of contaminants. These standards define levels that the Minister deems to be acceptable for the protection of the environment, including human life, wildlife and vegetation. By their very nature, the ambient air quality standards are based on the emissions from all potential sources within an airshed. For some pollutants, such as sulphur dioxide, the number of potential sources in an airshed contributing to the concentrations in ambient air would be limited due to the chemistry involved in the formation of sulphur dioxide. For other pollutants, such as particulate matter, the number of potential sources in an airshed can be quite large, and difficult to assign to any particular source. To determine the ambient levels of a particular pollutant, typically a series of monitors are located within the airshed. If the level of a pollutant exceeds the corresponding ambient air quality standard, then by Section 3 of the Air Pollution Control Regulations, the Minister can specify conditions in an approval or develop an air quality management plan for the airshed. However, it is often the case that in an airshed which includes major industrial operations, the series of monitors do not record an ambient concentration in excess of the associated standard, yet an exceedance of the ambient air standard was likely to have occurred in an area where a monitor was not located. To address compliance with the ambient standards, the Department of Environment and Conservation developed guidance document GD-PPD Compliance Determination. 3

4 In that guidance document, compliance is to be determined by a registered dispersion model, or more specifically, in accordance with the terms and conditions of this particular Guidance Document. For this 1 st revision, numerous conditions were adjusted to account for model updates and improved algorithms in the approved models and associated preprocessors. As well, various usage conditions were modified to account for new technologies. This revision also incorporates, in Section 9, the provisions of Guidance Document GD- PPD-029 NO x Modelling Results, and as such, that Guidance Document is hereby rescinded. DEFINITIONS In this guidance document: (a) (b) (c) (d) (e) administrative boundary means the boundary, as defined in a Certificate of Approval, for the administration of the Air Pollution Control Regulations. AAERMOD modelling system@ means the modelling system developed by United States Environmental Protection Agency (US EPA) in conjunction with the American Meteorological Society (AMS) and includes the AERMET meteorological preprocessor, the AERMAP terrain preprocessor, and the AERMOD dispersion model; Aair contaminant@ means any discharge, release, or other propagation into the air and includes, but is not limited to, dust, fumes, mist, smoke, particulate matter, vapours, gases, odours, odorous substances, acids, soot, grime or any combination of them; ACALPUFF modelling system@ means the modelling system developed by scientists at the Atmospheric Studies Group and includes the CALMET meteorological preprocessor, the CALPUFF dispersion model, the CALPOST postprocessor, and associated preprocessing programs; Adepartment@ means the Department of Environment and Conservation and it=s successors; 4

5 1. APPROVED MODELS For all regulatory applications, the CALPUFF modelling system is approved, subject to the terms and conditions outlined in Section 11. Under special circumstances outlined in Sections 5 and 6, and with the prior approval of the department, the US EPA model SCREEN3 and the AERMOD modelling system, may be approved for regulatory applications. If a circumstance exists where the CALPUFF modelling system, or alternatively the AERMOD modelling system or the SCREEN3 model is not appropriate, the department will review, on a case by case basis, the appropriateness of alternate models and define the terms and conditions under which an alternate model will be employed. 2. CALPUFF MODELLING SYSTEM - OVERVIEW The CALPUFF modelling system includes three main components: CALMET, CALPUFF and CALPOST, and a series of preprocessing programs designed to interface the model with routinely-available meteorological and geophysical datasets. CALMET is a meteorological model that develops hourly wind and temperature fields on a threedimensional gridded modelling domain. Associated two-dimensional fields such as mixing heights, surface characteristics and dispersion properties are also included in the file produced by CALMET. CALPUFF is a transport and dispersion model that advects Apuffs@ of material emitted from modelled sources, simulating dispersion and transformation processes along the way. It typically uses the fields generated by CALMET, or as an option, uses simpler non-gridded meteorological data much like the existing plume models. Temporal and spatial variations in the meteorological fields selected are explicitly incorporated in the resulting distribution of puffs throughout a simulation period. The primary output files from CALPUFF contain either hourly concentrations or hourly deposition fluxes evaluated at selected receptor locations. CALPOST is used to process these files, producing tabulations that summarize the results of the simulation, identifying, for example, the highest and second highest 1-hour average concentrations at each receptor. When performing visibility-related modelling, CALPOST uses concentrations from CALPUFF to compute extinction coefficients and related measures of visibility, reporting these for selected averaging times and location. 1 5

6 3. AERMOD MODELLING SYSTEM - OVERVIEW The AERMOD modelling system includes three main components: AERMET, AERMAP and AERMOD. AERMET is a general purpose meteorological preprocessor for organizing available meteorological data, and requires the input of surface roughness, Bowen ratio and albedo together with morning upper air soundings and hourly observations of wind speed, wind direction, cloud cover and temperature. AERMAP is a terrain preprocessor whose primary purpose is to determine the height scale for each receptor in the modelling domain. AERMOD is a steady-state plume dispersion model for assessment of pollutant concentrations from a variety of sources. AERMOD simulates transport and dispersion from multiple point, area, or volume sources based on an up-to-date characterization of the atmospheric boundary layer. 2,3 4. US EPA SCREEN3 MODEL - OVERVIEW SCREEN3 is a Gaussian plume model that incorporates source-related factors and meteorological factors to estimate pollutant concentration from continuous sources. It assumes that the pollutant does not undergo any chemical reactions, and that no other removal processes, such as wet or dry deposition, act on the plume during its transport from the source. SCREEN3 performs all of the single source, short-term calculations including estimating maximum ground-level concentrations and the distance to the maximum, incorporating the effects of building downwash on the maximum concentrations for both the near wake and far wake regions, estimating concentrations in the cavity recirculation zone, estimating concentrations due to inversion break-up and shoreline fumigation, and determining plume rise for flare releases. SCREEN3 can not explicitly determine maximum impacts from multiple sources SCREEN3 MODEL - SPECIAL CIRCUMSTANCES The SCREEN3 model may be approved for regulatory applications provided the application does not involve situations denoted in Table 5.1 and; 1) has annual emissions, for all pollutants, less than those denoted in Table 5.2; or 2) has annual emissions, for at least one pollutant, in excess of those denoted in Table 5.2, but the department has deemed the use of the model as adequate for the application. 6

7 Table 5.1 Applications where SCREEN3 is not acceptable Multiple sources On-site meteorological data required Terrain elevations vary about the sources Complex fumigation calculations More than 1 downwash structure exists Particulate size fractionation required Table 5.2 Pollutant Annual Emission Limit for using SCREEN3 (kilograms) sulphur dioxide (SO 2 ) 5000 total suspended particulate (TSP) 1000 particulate matter less than 10 microns (PM 10 ) 500 particulate matter less than 2.5 microns (PM 2.5 ) 250 nitrogen oxides (NO x ) 5000 For pollutants not listed in Table 5.2, but where the use of SCREEN3 may otherwise be approved, the department shall determine, on a case by case basis, if SCREEN3 may be applied. If SCREEN3 indicates a potential violation of the Air Pollution Control Regulations or a condition of a Certificate of Approval, then the department may require the use of either the AERMOD modelling system or the CALPUFF modelling system. In such circumstances, the application shall adhere to the provisions of Sections 10 or 11 respectively. Examples of regulatory applications for which SCREEN3 may be approved include: - single source diesel powered electrical generators - space heating of small rectangular buildings - VOC emissions from small autobody shops - single flare oil production wells. 7

8 6. AERMOD MODELLING SYSTEM - SPECIAL CIRCUMSTANCES The AERMOD modelling system, as detailed in Section 10, may be approved for regulatory application if the application does not involve situations denoted in Table 6.1. If an application involves a circumstance denoted in Table 6.1, the application shall adhere to the provisions of the CALPUFF modelling system detailed in Section 11. Should this guidance document require the use of CALPUFF for regulatory application, but the use of the AERMOD modelling system was previously approved by an existing Certificate of Approval, the AERMOD modelling system may be used until the expiration of the Certificate of Approval or is otherwise replaced by another Certificate of Approval. The requirements of this guidance document shall be reflected in any future Certificate of Approval. Table 6.1 Applications where the AERMOD modelling system is not acceptable Long range transport (> 50km) Overwater and coastal interaction effects Temporal analysis required Visibility-related postprocessing Chemical transformations present Subgrid scaling of complex terrain 8

9 7. POLLUTANTS TO BE MODELLED Unless otherwise specified under an approval issued by the department, the minimum number of pollutants to be modelled is listed in Table 7.1. Table 7.1 Pollutant Combustion Sources Non- Combustion Sources sulphur dioxide (SO 2 ) total suspended particulate (TSP) particulate matter less than 10 microns (PM 10 ) particulate matter less than 2.5 microns (PM 2.5 ) nitrogen dioxide (NO 2 ) carbon monoxide (CO) Where other pollutants are deemed by the department to have the potential to exceed the limits established in the Air Pollution Control Regulations or otherwise have an adverse affect on the environment, the department reserves the right to require the modelling of these other pollutants. 8. AVERAGING PERIODS TO BE MODELLED For regulatory applications in which the SCREEN3 model is approved by the department, the averaging period to be modelled for all pollutants denoted in Section 7 is 1 hour. For all other regulatory applications, the averaging periods to be modelled for all pollutants denoted in Section 7 are contained in Table 8.1. Where concentrations are modelled, the results shall be reported in micrograms per cubic metre (µg/m 3 ). Where deposition is modelled, the results shall be reported in micrograms per square metre (µg/m 2 ). The minimum output requirement is the maximum concentration at each receptor for the time frames denoted in Table 8.1 over the meteorological period defined in Sections 10 and 11. 9

10 Table 8.1 Pollutant sulphur dioxide (SO 2 ) Averaging Period 1 hour, 3 hour, 24 hour, annual total suspended particulate (TSP) particulate matter less than 10 microns (PM 10 ) particulate matter less than 2.5 microns (PM 2.5 ) nitrogen dioxide (NO 2 ) carbon monoxide (CO) 1 hour, 24 hour, annual 1 hour, 24 hour 1 hour, 24 hour 1 hour, 24 hour, annual 1 hour, 8 hour Where modelling of other pollutants is required under Section 7, such modelling shall be conducted for the averaging periods specified by the department. 9. NO X VS NO NO X FORMATION AND PRIMARY CONTROL In a combustion process, NO x is produced through 3 mechanisms, namely thermal NO x, fuel NO x and prompt NO x. (a) (b) (c) Thermal NO x is the primary source of NO x and is formed as a high temperature dissociation and subsequent reaction of nitrogen (N 2 ) and oxygen (O 2 ). It is produced in the hottest part of the flame and its formation increases exponentially with the flame temperature. The control of thermal NO x, is generally achieved through reducing the flame temperature, reducing the residence time, or by operating under fuel rich conditions. Fuel NO x is formed by the reaction of nitrogen compounds chemically bound in liquid or solid fuels with oxygen in the combustion air. In the combustion of such fuels, fuel NO x can account for up to 50% of the total NO x emissions. As heavier fuels tend to have higher levels of bound nitrogen, whereas gaseous fuels have minimal bound nitrogen, the principal control of fuel NO x is through conversion to light fuels or gaseous fuels. Prompt NO x is formed from the rapid reaction of atmospheric nitrogen with hydrocarbon radicals, and typically under partially fuel-rich conditions. It can be reduced through combustion staging or by operating under highly oxidizing combustion conditions. 10

11 9.2 NO X FROM INDUSTRIAL SOURCES The main industrial sources of NO x emissions in Newfoundland and Labrador are from the burning of fossil fuels to either generate steam for assorted processes or to generate electricity. In power boilers: (a) (b) (c) NO x formation is primarily through thermal NO x and fuel NO x, with minimal prompt NO x. Thermal NO x formation is dependent on peak temperature, and proportional to the nitrogen concentration in the flame, the oxygen concentration in the flame, and the residence time. Increases in flame temperature, oxygen availability, and/or residence time at high temperatures leads to an increase in NO x production. It is the dominant NO x forming mechanism in units firing distillate oils primarily because of the negligible nitrogen content in these fuels. Fuel nitrogen conversion is the more important NO x forming mechanism in residual oil boilers. The percent conversion of fuel nitrogen to NO x varies, however, typically from 20 to 90 percent of nitrogen in oil is converted to NO x. In gas turbines: (a) (b) (c) (d) (e) NO x formation occurs by all three mechanisms. Thermal NO x, arises from the thermal dissociation and subsequent reaction of nitrogen and oxygen molecules in the combustion air. Most thermal NO x is formed in high temperature stoichiometric flame pockets downstream of the fuel injectors where combustion air has mixed sufficiently with the fuel to produce the peak temperature fuel / air interface. Prompt NO x is formed from early reactions of nitrogen molecules in the combustion air and hydrocarbon radicals from the fuel. It is formed within the flame and is usually negligible when compared to the amount of thermal NO x formed. Fuel NO x, stems from the evolution and reaction of fuel-bound nitrogen compounds with oxygen. Fuel NO x from distillate oil-fired turbines may become significant in turbines equipped with a high degree of thermal NO x controls. The maximum thermal NO x formation occurs at a slightly fuel-lean mixture because of excess oxygen available for reaction. The control of stoichiometry is critical in achieving reductions in thermal NO x. Thermal NO x formation also decreases rapidly as the temperature drops below the 11

12 adiabatic flame temperature for a given stoichiometry. Maximum reduction of thermal NO x can be achieved by control of both the combustion temperature and the stoichiometry. Gas turbines operate with high overall levels of excess air because they use combustion air dilution as the means to maintain the turbine inlet temperature below design limits. In older gas turbines, where combustion is in the form of a diffusion flame, most of the dilution occurs downstream of the primary flame, which does not minimize peak temperature in the flame and suppress NO x formation. In internal combustion engines: (a) NO x formation occurs primarily as thermal NO x which arises from the thermal dissociation and subsequent reaction of nitrogen and oxygen molecules in the combustion air. Most thermal NO x is formed in the hightemperature region of the flame from dissociated molecular nitrogen in the combustion air. Some prompt NO x is formed in the early part of the flame from reaction of nitrogen intermediary species, and hydrocarbon radicals in the flame. Fuel NO x is virtually non existent. 9.3 BASIC NO x CHEMISTRY IN THE ATMOSPHERE In its simplest form, the basic NO x chemistry can be considered a cycle of continual reactions. NO x emissions from a source are typically considered to be a combination of NO and NO 2. As the exhaust leaves the stack and mixes with the ambient air, the NO reacts with ambient ozone (O 3 ) to form NO 2 and O 2. In the presence of ultraviolet radiation from the sun, NO 2 gets broken down into NO and O. O and O 2 react with a third molecule (M) such as O 2 or N 2 to form O 3 and the third molecule. NO + O 3! NO 2 + O 2 NO 2 + µv! NO + O O + O 2 + M! O 3 + M In the presence, of hydrocarbons (HCs), NO may also react to also form NO 2 via the following reaction: NO + HC! NO 2 + HC 9.4 NO 2 NO 2 is the primary component of concern in NO x. NO 2 is a reddish brown gas with a pungent odour, which upon reaction with other atmospheric compounds, becomes a major contributor to smog, acid rain, inhalable particulates and 12

13 reduced visibility. At significant levels and exposure, inhalation may result in irritation and burning to the skin and eyes, nose and throat. Prolonged exposure may result in permanent lung damage. 9.5 DISPERSION MODELLING INTERPRETATION The assumption historically has been that all of the NO x being emitted from a source has been in the form of NO 2. Research, however, has indicated that this approach is conservative and that in reality only a relatively small fraction of the total NO x emissions are in the form of NO 2. Further NO 2 will be produced however, based on the above noted reactions once the NO x plume leaves the stack, the extent to which is largely dependent on the level of O 3 in the atmosphere. Consequently when a source was being modelled for compliance with the Air Pollution Control Regulations, results may have shown noncompliance when in actuality there may have been compliance. The other major contributing factor to the determining the concentration of NO 2 is the lack of actual in-stack emission data which speciates NO x into NO 2 and NO. Both stack sampling programs and combustion equipment manufacturers cite emissions as total NO x, not NO 2 or NO. Consequently there is only a small volume of information readily available to draw upon to determine the baseline emission rates and subsequent atmospheric emission rates. 9.6 GUIDANCE For all applications, the Plume Volume Molar Ratio Method (PVMRM) is the preferred approach to evaluate NO 2 emissions. Where a facility wishes to measure the in-stack ratio of NO 2 / NO x then the department will consider using such data only after a representative sample has been obtained from the facility, or where a representative sample has been obtained from similar facilities. Where a facility wishes to measure the on-site ambient O 3 levels, then the department will consider using such data for evaluation of that facility only. Such in-stack data and/or ambient data shall be obtained using methods acceptable to the department. For the determination of predicted NO 2 concentrations when information on the in-stack emissions of NO and NO 2 are not available, the acceptable in-stack ratios for modelling purposes are listed in Table

14 Table 9.1 Emission Source In-stack NO 2 / NO x ratio Power Boilers 0.1 Compressors and Gas Turbines 0.6 Diesel Power Generating Units 0.2 The acceptable hourly O 3 background concentrations in lieu of on-site measured levels, is 50 ppb (98 µg/m 3 ). It is recognized that AERMOD can accommodate the PVMRM algorithm directly whereas CALPUFF does not at this time. As such, results from CALPUFF will have to be post processed to conform with the PVMRM algorithm. 10. AERMOD MODELLING SYSTEM - MODELLING PROVISIONS When modelling with the AERMOD modelling system, the following minimum specifications shall be required as model inputs: 10.1 AERMET (a) (b) Meteorological data inputs shall consist of observations extracted from twice daily upper air soundings together with hourly surface data from an on-site meteorological station and/or nearest Environment Canada meteorological station. Where sufficient meteorological data from an onsite station is available, a minimum data record of 1 year is required for regulatory applications. Where sufficient meteorological data from an onsite station is not available, then a minimum data record of 3 years is required consisting of on-site data supplemented with data from the nearest Environment Canada meteorological station. Where no on-site data is available, then a minimum data record of 5 years is required from the nearest Environment Canada meteorological station. Data from an Environment Canada meteorological station can be obtained from the Atlantic Climate Centre in Fredericton NB. Upper air sounding data can be obtained from the Atlantic Climate Centre in Fredericton NB, or the National Climatic Data Center (NCDC) in the United States. Data extracted from the twice daily upper air soundings shall extend to the 500 mb level and shall incorporate all sounding levels (mandatory, significant, etc.), including the surface level and 500 mb level. Data to be extracted at each level includes, pressure, altitude, temperature, dew point temperature, wind direction and wind speed. The upper air soundings are to be taken from the most representative upper air station. Where a 14

15 facility is approximately equidistant from 2 or more upper air stations, the choice of the upper air station will be dependent on the direction of the upper air stations from the facility, the terrain elevation of the facility vs the terrain elevation of the upper air station, and the proximity of the facility and upper air station to large water bodies. Table 10.1 provides general guidance on choosing the appropriate upper station. Table 10.1 Location Eastern Newfoundland Central and Western Newfoundland Coastal and Central Labrador Western Labrador Alternate 1 Alternate 2 Upper Air Station St. John s Stephenville Goose Bay La Grande IV Sept Isle Kuujjuaq Latitude / Longitude N W N W N W N W N W N W (c) (d) (e) (f) Sufficient on-site meteorological data includes: wind speed, wind direction, ambient temperature, barometric pressure and opaque cloud cover (or alternatively total cloud cover). Meteorological data from an Environment Canada station shall include: wind speed, wind direction, ambient temperature, barometric pressure, opaque cloud, total cover, ceiling height and relative humidity. Albedo, Bowen ratio and surface roughness may be taken as seasonal values, though monthly is preferred, for a minimum of 4 direction sectors. Each sector shall be representative of the prevalent site characteristics, and need not be equal in dimension. In situations where the site characteristics are not explicitly defined within the generally available literature and tables, pre-approval of the albedo, bowen ratio and surface roughness values is required. All wind directions are to be randomized to 1º, either prior to using AERMET or through the METHOD command in AERMET. Only results from the latest version of AERMET shall be acceptable. As of the date of this guidance document, the version was The department shall be contacted prior to undertaking compliance modelling to confirm the latest acceptable version. 15

16 10.2 AERMAP (a) (b) (c) All applications are required to employ terrain effects, and calculate effects at ground-level. Terrain elevation data shall be extracted from digital elevation mapping available from the Department of Environment and Conservation (Lands Branch), National Resources Canada or Shuttle Radar Topography Mission (SRTM). Terrain elevations shall be extracted from maps scaled to 3 arcseconds or better using UTM (Universal Traverse Mercator) projection, reference ellipsoid NAD83 or WGS84. Terrain receptors shall incorporate a rectangular Cartesian grid coupled with discrete receptors using the UTM coordinate system as noted above. The maximum spacing, on and off property, shall be: 1) 50 m spacing from the centre of the operation out to 500 m, 2) 100 metre spacing from 500 m out to 1000 m, 3) 200 metre spacing from 1000 m out to 2000 m 4) 500 metre spacing beyond 2000 km, 5) 50 metre spacing within all residential areas located less than 1000 m of property s administrative boundary, 6) 100 metre spacing within all residential areas located beyond 1000 m of property s administrative boundary, but located within 2000 m of the property s administrative boundary, 7) 200 metre spacing within all residential areas located beyond 2000 m of property s administrative boundary. Discrete receptors are to be placed along the property s administrative boundary at 20 metre intervals or less. The physical extent of the spacing requirement shall be determined after consultation with the department. (d) (e) For the purposes of the guidance document, the centre of the operation is defined as the location that minimizes the distance from all emitting sources, weighted to the emission rates of the contributing sources. Only results from the latest version of AERMAP shall be acceptable. As of the date of this guidance document, the version was The department shall be contacted prior to undertaking compliance modelling to confirm the latest acceptable version AERMOD (a) Building downwash must be accounted for when it exists. As a general rule of thumb, if a building height is greater than 40% of the source emission height, then there is building downwash. 16

17 (b) Building downwash variables shall be calculated for the Plume Rise Model Enhancements (PRIME) algorithm with the appropriate output variables serving as inputs into AERMOD. These variables are (variable name): 1) direction specific building height (BUILDHGT), 2) direction specific building width (BUILDWID), 3) direction specific along flow building length (BUILDLEN), 4) along flow distance from the stack to centre of upwind face of the projected building (XBADJ), 5) across flow distance from the stack to centre of upwind face of the projected building (YBADJ). (c) (d) (e) (f) The application is to be employed in regulatory default mode. The application is to be employed without flagpole heights. Source emission parameters shall be taken from the most recent stack test conducted in accordance with departmental guidance document GD- PPD If no stack parameters exist, then source inputs to the model shall be made only in consultation with the department. Only results from the latest version of AERMOD shall be acceptable. As of the date of this guidance document, the version was The department shall be contacted prior to undertaking compliance modelling to confirm the latest acceptable version. 11. CALPUFF MODELLING SYSTEM - MODELLING PROVISIONS When modelling with the CALPUFF modelling system, the following minimum specifications shall be required as model inputs: 11.1 CALMET (a) Meteorological data inputs shall consist of observations extracted from twice daily upper air soundings together with hourly surface data from an on-site meteorological station and/or nearest Environment Canada meteorological station. Where sufficient meteorological data from an onsite station is available, a minimum data record of 1 year is required for regulatory applications. Where sufficient meteorological data from an onsite station is not available, then a minimum data record of 2 years is required consisting of on-site data supplemented with data from the nearest Environment Canada meteorological station. Where no on-site data is available, then a minimum data record of 3 years is required from the nearest Environment Canada meteorological station. Data from an Environment Canada meteorological station can be obtained from the 17

18 Atlantic Climate Centre in Fredericton NB. Upper air sounding data can be obtained from the Atlantic Climate Centre in Fredericton NB, or the National Climatic Data Center (NCDC) in the United States. (b) Data extracted from the twice daily upper air soundings shall extend to the 500 mb level and shall incorporate all sounding levels (mandatory, significant, etc.), including the surface level and 500 mb level. Data to be extracted at each level includes, pressure, altitude, temperature, dew point temperature, wind direction and wind speed. The upper air soundings are to be taken from the most representative upper air station. Where a facility is approximately equidistant from 2 or more upper air stations, the choice of the upper air station will be dependent on the direction of the upper air stations from the facility, the terrain elevation of the facility vs the terrain elevation of the upper air station, and the proximity of the facility and upper air station to large water bodies. Table 11.1 provides general guidance on choosing the appropriate upper station, however since CALMET can accommodate data from numerous upper air stations, in these circumstances, data from all pertinent stations should be used. Table 11.1 Location Eastern Newfoundland Central and Western Newfoundland Coastal and Central Labrador Western Labrador Alternate 1 Alternate 2 Upper Air Station St. John s Stephenville Goose Bay La Grande IV Sept Isle Kuujjuaq Latitude / Longitude N W N W N W N W N W N W (c) (d) Sufficient on-site meteorological data includes: wind speed, wind direction, ambient temperature, barometric pressure and opaque cloud cover (or alternatively total cloud cover). Meteorological data from an Environment Canada station shall include: wind speed, wind direction, ambient temperature, barometric pressure, opaque cloud, total cover, ceiling height and relative humidity. It is recognized that CALMET can accept mesoscale meteorological model inputs such as those from the ETA model and the Nonhydrostatic Mesoscale Model (NMM). In such circumstances, an effective meteorological windfield can be generated for the facility being modelled. 18

19 As such, a minimum data record of 1 year is required for regulatory applications. (e) (f) (g) (h) (i) (j) (k) (l) The meteorological grid shall be rectangular Cartesian, and shall be sufficiently large to encompass the entire modelling domain. Nodal spacing within the grid shall be a maximum of 1000 metres, but where terrain varies significantly about the facility, a meteorological grid of smaller spacing may be required. In the vertical, a minimum of 7 cell face heights are required, the heights of which are dependent of the nature of the facility being modelled and the surrounding terrain. The bias at each cell face height shall be determined only after consultation with the department. Where sea breezes are likely to affect the dispersion of a pollutant from a facility located in close proximity to the ocean, the effects must be considered. In this case, sea surface meteorological parameters must be extracted from a representative station. Though hourly is preferred, parameters recorded weekly or monthly may be acceptable. Albedo, bowen ratio, surface roughness, soil heat flux, anthropogenic heat flux, leaf area index and land use parameters are to be determined for each node of the meteorological grid. In situations where these characteristics are not readily available from the Lands branch of the Department of Environment and Conservation or from other sources, the Environment branch of the Department of Environment and Conservation shall be contacted for appropriate guidance. Terrain elevation data shall be extracted from digital elevation mapping available from the Department of Environment and Conservation (Lands Branch), National Resources Canada or Shuttle Radar Topography Mission (SRTM). Terrain elevations shall be extracted from maps scaled to 3 arcseconds or better using UTM (Universal Traverse Mercator) projection, reference ellipsoid NAD83 or WGS84. All parameters of the input file are to be set at default. Wind directions are to be randomized to 1º or better. Where only one surface meteorological station exists in the meteorological grid, the LVARY variable, specifying the radius of influence of the meteorological data, shall be set to true. If more than one surface meteorological station exists, then appropriate values of RMAX1, RMAX2 and RMAX3 need to be defined based on the topography of the meteorological grid. Only results from the latest version of CALMET shall be acceptable. As of the date of this guidance document, the version was 6.211, level The department shall be contacted prior to undertaking compliance modelling to confirm the latest acceptable version. 19

20 11.2 CALPUFF (a) Terrain receptors shall incorporate a rectangular Cartesian grid coupled with discrete receptors using the UTM coordinate system as noted above. The maximum spacing, on and off property, shall be: 1) 50 m spacing from the centre of the operation out to 500 m, 2) 100 metre spacing from 500 m out to 1000 m, 3) 200 metre spacing from 1000 m out to 2000 m 4) 500 metre spacing beyond 2000 km, 5) 50 metre spacing within all residential areas located less than 1000 m of property s administrative boundary, 6) 100 metre spacing within all residential areas located beyond 1000 m of property s administrative boundary, but located within 2000 m of the property s administrative boundary, 7) 200 metre spacing within all residential areas located beyond 2000 m of property s administrative boundary. Discrete receptors are to be placed along the property s administrative boundary at 20 metre intervals or less. The physical extent of the spacing requirement shall be determined after consultation with the department. (b) The computational grid shall be sized such that it extends a minimum of 1 km beyond the outer extent of the receptor grid in all directions to allow for puffs to reintegrate onto the receptor grid in the event of wind directional changes. (c) (d) Building downwash must be accounted for when it exists. As a general rule of thumb, if a building height is greater than 40% of the source emission height, then there is building downwash. Building downwash variables shall be calculated for the Plume Rise Model Enhancements (PRIME) algorithm with the appropriate output variables serving as inputs into AERMOD. These variables are (variable name): 1) direction specific building height (BUILDHGT), 2) direction specific building width (BUILDWID), 3) direction specific along flow building length (BUILDLEN), 4) along flow distance from the stack to centre of upwind face of the projected building (XBADJ), 5) across flow distance from the stack to centre of upwind face of the projected building (YBADJ). 20

21 (e) All parameters of the input file are to be set at default unless justification exists to the contrary. In situations where the default parameters are not justified for modelling, such as modelling for wet removal and dry deposition, the department shall be contacted for guidance. Irrespective of these situations, for the following parameters, the required values shall be: Parameter Name Value MSHEAR - Wind shear above stack top 1 MSPLIT - Puff splitting allowed 1 MDISP - Dispersion coefficient method 2 (f) (g) (h) In situations where the prediction of near source concentrations are desired, CALPUFF shall be run in slug mode, i.e. parameter MSLUG= 1, versus puff mode. Source emission parameters shall be taken from the most recent stack test conducted in accordance with departmental guidance document GD- PPD If no stack parameters exist, then source inputs to the model shall be made only in consultation with the department. Only results from the latest version of CALPUFF shall be acceptable. As of the date of this guidance document, the version was 6.112, level The department shall be contacted prior to undertaking compliance modelling to confirm the latest acceptable version CALPOST (a) (b) All parameters of the input file, subject to the provisions of Section 8, are to be set at default unless justification exists to the contrary. Only results from the latest version of CALPOST shall be acceptable. As of the date of this guidance document, the version was 6.131, level The department shall be contacted prior to undertaking compliance modelling to confirm the latest acceptable version. 12. REPORTING The modelling report shall be submitted to the department within 120 days of completion of a source emission test as defined in an approval issued to the industry, or in accordance with departmental guidance document GD-PPD The modelling report shall include: 21

22 (a) (b) (c) isopleths for the pollutants listed in Section 7 over the time frames specified in Table 8.1, superimposed on a map defining major roads, buildings, structures, landmarks. a listing of model input parameters including a copy of the input and output files. accompanying discussion of the results. 13. BPIP The Building Projection Input Program (BPIP) has been traditionally used to determine the building wake effects for input into either the AERMOD or CALPUFF modelling systems. However, it has been determined that in certain circumstances, BPIP may produce results that are not entirely accurate for the structure being modelled. As such, all building downwash input must be approved by the department prior to modelling. 14. REFERENCES 1. Scire, J.S, D.G. Strimaitis and R.J. Yamartino, 2000: A User=s Guide for the CALPUFF Dispersion Model. Earth Tech Inc., Concord MA. 2. U.S. Environmental Protection Agency, 1998: User=s Guide for the AERMOD Meteorological Preprocessor (AERMET). U.S. Environmental Protection Agency, Research Triangle Park, NC. 3. U.S. Environmental Protection Agency, 2000: 40 CFR Part 51, Guideline on Air Quality Models, Proposed Rule. U.S. Environmental Protection Agency. 4. U.S. Environmental Protection Agency, 1995: Screen3 Model User=s Guide. U.S. Environmental Protection Agency, Research Triangle Park, NC. G.G Akopova, N.A. Solovyova et al, 2002: Transformation of NO to NO2 in the Exhaust Plumes from Gas Compressor Stations. Atmospheric Chemistry within the Earth System from Regional Pollution to Global Change, Greece. Alpha-Gamma Technologies Inc, 2000: Emission Factor Documentation for AP- 42 Section 3.1 Stationary Gas Turbines. Raleigh, NC. 22

23 R. Bell & F Buckingham. An Overview of Technologies for Reduction of Nitrous Oxides Emissions. MPR Associates Inc, Alexandria, VA. Clark, Larry 2002: Controlling NOx. Process Heating. Eastern Research Group, 1998: Report on Revisions to 5th Edition AP-42 Section 1.3 Fuel Oil Combustion. Morrisville, NC. P. L. Hanrahan, 1999: The Plume Volume Molar Ratio Method for Determining NO2/NOx Ratios in Modeling. Air Quality Division, Oregon Department of Environmental Quality, Portland, Oregon. D. Laxen & P. Wilson, 2002: A New Approach to Deriving NO2 from NOx for Air Quality Assessments of Roads. Air Quality Consultants Ltd, Bristol, UK. MACTEC Federal Programs, Inc, Sensitivity Analysis of PVMRM and OLM in AERMOD. MACTEC Federal Programs, Inc, Research Triangle Park, NC. Oakridge National Laboratory, 2002: Guide to Low Emission Boiler and Combustion Equipment Selection. Oakridge, TN. U.S. Environmental Protection Agency, 1998: Compilation of Air Pollution Emission Factors, AP-42, Section 1.3, Fuel Oil Combustion. U.S. Environmental Protection Agency, Research Triangle Park, NC. U.S. Environmental Protection Agency, 2000: Compilation of Air Pollution Emission Factors, AP-42, Section 3.1, Stationary Gas Turbines. U.S. Environmental Protection Agency, Research Triangle Park, NC. U.S. Environmental Protection Agency, 1996: Compilation of Air Pollution Emission Factors, AP-42, Section 3.3, Gasoline and Diesel Industrial Engines. U.S. Environmental Protection Agency, Research Triangle Park, NC. U.S. Environmental Protection Agency, 1996: Use of the Ozone Limiting Method for Estimating Nitrogen Dioxide Concentrations. U.S. Environmental Protection Agency, Research Triangle Park, NC. 23