Operating Conditions

8. Operating conditions

Facility operating conditions affect contaminant emission rates and emission rates are key inputs to the use of the approved models and assessment of POI concentrations. The purpose of this portion of an ESDM report is to document both the facility operating conditions (that are relevant to estimating emission rates) and the development of emission rate estimates for the significant air contaminants discharged from the facility.

Section 10 of the Regulation relates to facility operating conditions. Section 11 sets out the requirements for emission rates. In general, section 12 sets out the requirements to “refine” emission rate estimates^{footnote 12[12]} when the combined effect of sections 10 and 11 result in predictions of exceedences of ministry POI Limits. In summary, sections 10, 11 and 12 of the Regulation work together to ensure that the assessment of maximum POI concentration are as accurate as possible and do not under-estimate actual concentrations.

8.1 Operating Conditions

Operating conditions provide key information to the development of emission rate estimates. For example, operating conditions link to production information which are often the basis for emission factors used for emission rate estimates. Subsection 10 (1) of the Regulation states:

Subsection 10 (1) of the Regulation allows a choice between the scenarios described in paragraphs 1 and 2 of this subsection. In other words, when using an approved dispersion model, a person may choose to assume conservative operating conditions or to use actual operating conditions from the previous year. In situations, where the actual operating condition (e.g., from the previous year) is used to assess compliance with the ministry POI Limits, it will also be necessary to verify compliance according to the operating condition allowed by the most recent ECA issued and its approved production limit. A facility that uses actual operating conditions (e.g. from the previous year) in its ESDM report to assess compliance with the ministry POI Limits may have its operation restrained in its ECA to the actual operating condition used in its ESDM report.

Although subsection 10 (1) allows a choice of operating conditions, section 12 of the Regulation may require the use of the scenario described in paragraph 2 of subsection 10 (1) if an exceedence of a standard results from the use of a scenario based upon paragraph 1 of this section (see subsection 12 (2) of the Regulation for an exception to this requirement and see Chapter 9.3 Refinement of Emission Rates of this Procedure Document for more information).

For paragraph 1 of subsection 10 (1), the approved dispersion model must be used with operating conditions that result in the maximum POI concentration for each significant contaminant, according to the averaging period for the relevant ministry POI Limit corresponding to that contaminant. For example, a 24-hour average operating condition must be used when comparing to a ministry POI Limit that has a 24-hour averaging period. If a contaminant has more than one limit, then the operating conditions and averaging periods for all those limits must be assessed and included in the ESDM report.

The operating condition that corresponds to the maximum POI concentration may occur when the facility is at the maximum production level or running at a lower production level or the process is in transition (see Chapter 8.3 Transitional Operating Conditions for more information). Persons preparing an ESDM report must assess all operating scenarios to determine the scenario that results in the maximum POI concentration for that contaminant.

Determining the appropriate Operating Conditions should be based on the following:

• the averaging period for the ministry POI Limit(s) for the contaminant;
• information contained in the Facility Description of the ESDM report;
• simultaneous versus sequential operations and emission estimates that are based upon either design capacities or actual operating data; and
• technical and operational limitations on production.

Development of a Realistic Scenario that Results in the Highest Concentration

Many facilities have a combination of sources that emit the same contaminant. In some cases, the various sources emit the contaminant simultaneously while in other situations the contaminant is emitted at different times or sequentially from each source. Where there is a simultaneous emission of a contaminant, it may not be realistic, at some facilities, to assume that each individual source of contaminant is resulting in a maximum emission at the same time.

The following examples are intended to provide guidance in identifying a realistic assumption of the operating condition that results in the highest point of impingement concentration of a contaminant, as per paragraph 1 of subsection 11 (1). For more information on refinement of emissions, please refer to guidance for paragraphs 2 and 3 subsection 11 (1) in Chapter 9 Emission Rate Estimating And Data Quality.

Example Scenario 1: more than one source emitting the same contaminant at the same time. For this example, the operation of each source is linked to a common overall production rate and it is realistic to assume maximum emissions from each source of the contaminant occur simultaneously. To simplify the assessment, if a facility assumes that the sources are all emitting at the same time, and the assessment shows that the ministry POI limit is met, then no further assessment is necessary. If not, the operating scenario can be tailored to more closely simulate the operation of the facility.

Example Scenario 2: this is similar to Example 1 where there is more than one source emitting the same contaminant at the same time. However, for this example, the operation of each source of the same contaminant is not linked to the others and it is reasonable to assume that maximum emissions for each source are not occurring at the same time. In this situation, it would be realistic to assume the following scenario:

• maximum emission rate from the source of contaminant that has the largest contribution to the maximum POI concentration;
• maximum emission rate from the sources where it is reasonable to assume that these maximum emissions can occur simultaneously with the highest contributing source; and
• average emission rates for all other sources of contaminant that operate simultaneously.

Example Scenario 3: more than one source emitting the same contaminant but the emissions occur at different times. For this example, the scenario that results in the highest concentration would be based upon maximum emissions (for the relevant averaging period) from the source that has the largest contribution to the maximum POI concentration with an assumption of zero emissions for all other non-simultaneously operating sources. The use of the variable emission rate option in some dispersion modelling interfaces may also be a reasonable approach to address this type of situation; particularly when the averaging period for the relevant air standard is relatively long (e.g., annual-average).

To simplify the effort in selecting the operating condition that results in a maximum POI concentration for each significant contaminant, it may be possible to develop a common operating condition for similar contaminants. Operating conditions that are developed from an understanding of process interactions and operations may also simplify this task and result in common operating conditions for a variety of significant (non-negligible) contaminants. Paragraph 6 of subsection 26 (1) of the Regulation states the following regarding the documentation of operating conditions within an ESDM report:

To summarize, in accordance with paragraph 6, the ESDM report shall include a description of the operating condition for each contaminant that is emitted in significant amounts. This description of the operating condition for each significant contaminant should:

1. identify each significant source (or group of sources) of the contaminant;
2. describe the operating conditions of the significant sources that result in the maximum POI concentration for the contaminant, ensuring that the operating conditions correspond to the averaging period of the ministry POI Limit(s); and
3. be based upon information contained in the Facility Description section of the ESDM report with consideration for simultaneous versus sequential operations and emissions; design capacities versus actual operating data; technical and operational limitations on production and the terms and conditions of ECAs issued to the facility.

Table 8-1 Assessing Emissions At Operating Conditions That Result In Maximum POI Concentrations For Different Averaging Periods – Examples provides a series of examples for identifying operating conditions and developing emission rate estimates for different averaging periods.

Table 8-1: Assessing emissions at operating conditions that result in maximum POI concentrations for different averaging periods - examples

Using the Models in the Appendix to Regulation 346 in comparison to 1/2-hour average ministry POI Limits: Emission rates based on an operating condition, averaged over a ½ hour period that results in the maximum POI concentration must be developed as an input to the models. Output from the dispersion models must be compared to the ½-hour average ministry POI Limits, including standards in Schedule 2.

Using screen3screen3 or AERMOD in comparison to 1/2-hour average ministry POI Limits: Emission rates based on an operating condition, averaged over a ½ hour period, that results in the maximum POI concentration must be developed as an input to the models. Output from these dispersion models must be converted to ½ hr averages using the formula in section 17 and compared to the ½ hour average ministry POI Limits, including standards in Schedule 2 of the Regulation.

Using screen3, or AERMOD in comparison to 1-hour average ministry POI Limits: Emission rates based on an operating condition, averaged over a 1-hour period, that results in the maximum POI concentration must be developed as an input to the models. Output from the dispersion models must be compared to the 1-hour average ministry POI Limits, including standards in Schedule 3 of the Regulation.

Using screen3screen3, or AERMOD in comparison to 24-hour average ministry POI Limits: ^*Emission rates based on an operating condition, averaged over a 24-hr period, that results in the maximum POI concentration must be developed as an input to the models. Output from the dispersion models must be compared to the 24-hour average ministry POI Limits, including 24- hour average standards in Schedule 3 of the Regulation. This approach would also be used for 24-hour Upper Risk Thresholds in Schedule 6.

Note: The SCREEN3 dispersion model is only able to predict 1-hour average concentrations. These 1-hour results can be converted to a 24-hour average concentration by using the averaging period conversion factor set out in section 17 of the Regulation^**. In this case,^*emission rates would correspond to a maximum 24-hour average operating condition.

Using screen3, or AERMOD in comparison to annual average ministry POI Limits: ^*Emission rates based on an operating condition, averaged over a year period, that results in the maximum POI concentration must be developed as an input to the models. Output from the dispersion models must be compared to the annual average ministry POI Limits, including annual average standards in Schedule 3 of the Regulation.

Note: The screen3 dispersion model is only able to predict 1-hour average concentrations. These 1-hour results can be converted to an annual average concentration by using the averaging period conversion factor set out in section 17 of the Regulation^**. In this case,^*emission rates would correspond to a maximum annual average operating condition.

Note: Annual average emission rates must not be used as modelling inputs for ministry POI Limits with different averaging periods nor for URTs which are based on a 24 hour average emission rate.

Using screen3 or AERMOD in comparison to “X” – hour average ministry POI Limits:
^*Emission rates based upon an operating condition, averaged over an X-hour period, that results in the maximum POI concentration must be developed as an input to the models. Output from the dispersion models must be compared to the “X”-hour average ministry POI Limits, including the standards in Schedule 3 of the Regulation. This example is intended to illustrate that when using the appropriate dispersion model, the averaging period of the operating condition that represents the maximum POI concentration must be consistent with the averaging period of the corresponding ministry POI Limits.

Using ASHRAE in comparison to “X” – hour average ministry POI Limits: ^*Emission rates based upon an operating condition, averaged over an X-hour period, that results in the maximum POI concentration must be developed as an input to ASHRAE. Output from ASHRAE must be converted to “X” hour averaging times using the formula in section 17** to compare to the appropriate ministry POI Limits, including standards in Schedule 3 of the Regulation.

8.2 Multiple operating conditions

The Regulation may also require, in some cases, that ESDM reports be submitted with operational scenarios from both paragraphs 1 and 2 of section 10(1) as shown below.

ESDM reports prepared for URT exceedences (s.30) and Site-Specific Standards (s.32) are required to assess both of the operating scenarios described in subsection 10 (1) of the Regulation describing Operating Conditions, namely:

1. The conservative maximum operating scenario as set out in subsection 10 (1) paragraph 1; and
2. The scenario based on actual operating data from the previous year as set out in subsection 10 (1) paragraph 2.

Because both these ESDM reports under sections 30 and 33 of the Regulation involve assessments of POI concentrations above the standards, an assessment of frequency at specified human receptors is required. For more information on assessing frequency of exceedences see Chapter 13.2 Assessing Concentrations and Frequency at Specified POIs of this Procedure Document as well as Chapter 4.5 of the ministry document “Guideline for Implementation of air Standards in Ontario (GIASO)” (as amended) and Chapter 3.5 Assessing Concentrations and Frequency at Receptors of the “Guide to Requesting a Site-Specific Air Standard” (as amended).

8.3 Transitional operating conditions

This section is revoked, please refer to Section 10 of O. Reg. 419/05 amended on March 20^th, 2018.

8.4 Estimating emissions for different averaging periods

There is an interaction between s.10 (operating conditions), s.11 (emission rates) and s.13 (meteorological data) of the Regulation. The ministry already allows for some worst-case meteorological conditions to be discounted in the modelling by allowing the worst-case day per year or the highest 8 of the 1-hour values in a year to be discarded from the modelling results (see ADMGO)

There are often situations where contaminant emissions from sources are variable according to a time pattern and/or in accordance with specific conditions. Matching this variability with variable meteorological conditions can be particularly important for longer averaging periods. The dispersion modelling software such as AERMOD allow for the input of variable emissions, by hour, by week, by season and/or by wind speed. For more details on the use of this approach, please see the dispersion modelling documentation for the relevant approved model (e.g., AERMOD).

In addition, emission rate inputs depend on the averaging period that is relevant to the contaminant under review (e.g., use of the averaging period for the contaminant air standard). The following provides guidance on developing emission rate estimates for different averaging period scenarios^{footnote 13[13]}.

8.4.1 Estimating emissions for a maximum 1-hour averaging period (for contaminants with maximum 1-hour average standards)

Maximum 1-hour average emissions are generally developed either using maximum, 1- hour average measurement data or identifying the maximum 1-hour average for operating parameters that affect emissions of the contaminant (in conjunction with emission factors that are a function of these parameters).

Table 8.4.1: 1 Hour Averaging Period

Example 2.1a: Using Source Testing Data

• Stack testing campaigns were conducted for four different operating conditions for a source of emission. Source tests (each with three test runs), of at least one hour durations, were completed for each of the four operating conditions. The average emission rate, for each source test was 1 g/s, 1.5 g/s, 2.5 g/s and 3 g/s. In this example, the maximum 1-hour average emission rate for the tested source would be 3 g/s.

Example 2.1b: Combination of a Varying Operational Parameter and Emission Factors

• A process operating at full capacity is observed to have production rates that varied as follows over a 1-hour period: 1 unit of production per hour for the first fifteen minutes; 1.2 units per hour for the next 30 minutes; and 1.5 units for the last fifteen minutes. Emissions from this process were estimated (by past source tests on a similar set of processes) to be the following function of production:

  Emission Factor Equation: [10 g/s per hourly unit of production] × [units of production per hour]

  Therefore, maximum 1-hour average emissions = (1×0.25 + 1.2×0.5 + 1.5×0.25) × 10 = 12.25 g/s

  A third scenario involving estimating maximum 1-hour average emissions relates to emissions that occur over only a portion of an hour.

Example 2.1c: Part-Time Emissions

• Emissions from a process occur only for 20 minutes on an intermittent basis. Emissions are zero for the other 40 minutes in an hour. The maximum emissions, over a 20-minute period, were observed to be 1 g/s.

  Maximum 1-hour average emissions = (1 g/s) × (20 ⁄ 60) + (0 g/s) × (40 ⁄ 60) = 0.33 g/s

8.4.2 Estimating emissions for a maximum 24-hour averaging period (for contaminants with maximum 24-hour average standards)

The approach to estimating maximum 24-hour average emissions is similar to that used to estimate maximum 1-hour average emission estimates. However, situations where there is variation in emissions or where sources of contaminant are only operational for a fraction of the period are more common when estimating maximum 24-hour average emissions.

In addition, the dispersion models allow for the input of emission estimates on an hourly basis (also known as the “variable emissions input tool”). This allows for the matching of emissions with variations in meteorology over the 24-hour period.

Table 8.4.2: 24 Hour Averaging Period

Example 2.2a: Regular Variation in Emissions Over a 24-Hour Period; Five Days per Week

• Production and the emissions from a process are variable but regular and predictable and the same every day, five days per week. During the first 16 hours (of a 24-hour period), emissions are at a maximum of 1 g/s but only 0.5 g/s for the other 8 hours.

  In this situation, an appropriate approach would be to use the variable emissions input tool and input 1 g/s for the first 16 hours of the 24-hour period and 0.5 g/s for the other 8 hours.

Example 2.2b: Irregular Variation in Emissions Over a 24-Hour Period; Five Days per Week

• Production and the emissions from a process are variable and irregular over a 24-hour period but the pattern is the same for every day, five days per week. In this example, emissions of 1 g/s occur over any 16 hour period (not necessarily consecutive) and emissions are 0.5 g/s for the other 8 hours.

  One approach is to develop an overall average for the 24-hour period as a single input for the model run (and there is no need to use variable emissions input tool for this type of situation):

  Maximum 24-hour average emissions = (1 g/s) × (16 ⁄ 24) + (0.5 g/s) × (8 ⁄ 24) = 0.83 g/s
  (a single emission rate input for the modelling for each hour in the model run)

Example 2.2c: Irregular Variation in Emissions Over a 24-Hour Period; Five Days per Week with Occasionally Higher Emissions

• Production is generally the same as in example 2.2b, above, but a few days per year, the emissions increase to 3 g/s for 16 hours and 1 g/s for 8 hours.

  One approach is to develop an overall average for the “worst-case” 24-hour period as a single input for the model run and input this for each hour in the model run:

  Maximum 24-hour average emissions = (3 g/s) × (16 ⁄ 24) + (1 g/s) × (8 ⁄ 24) = 2.33 g/s
  (a single emission rate input for the modelling for each hour in the model run)

8.4.3 Estimating annual average emissions (for contaminants with annual average standards)

Estimating emissions on an annual-average basis includes consideration of variation in emissions on a daily, weekly and monthly basis.

The following general scenarios are intended to represent some common type of situations that affect how annual average emission estimates are developed for input into atmospheric dispersion models:

1. Source with intermittent and regular (i.e., same time of day) emissions, every day of the year.
2. Source with intermittent and irregular (i.e., any time of day) emissions, every day of the year.
3. Source with intermittent and irregular emissions, but only two days per week.
4. Source with intermittent and regular emissions, but for only the same two months per year.

Table 8.4.3: Annual Averaging Period

Example 2.3a: Intermittent and Regular (i.e., same time of day) Emissions; Every Day of the Year

• Source with intermittent (i.e., not constant) and regular (i.e., occur at the same time of day) emissions that average 1 g/s for any three hours between 6am and noon, every day of the year.

  Note: In this example, emissions between noon and 6am on the following day are zero.

  In this situation, an appropriate approach would be to use the variable emissions tool and input 0.5 g/s for each of the six hours between 6am and noon and 0 g/s for the remaining hours. This pattern would be applicable to every day in the year.

  Where, emissions input for 6am - Noon = 1 g/s × (3 hours ⁄ 6 hours) = 0.5 g/s

Example 2.3b: Intermittent and Irregular (i.e., any time of day) Emissions; Every Day of the Year

• Source with intermittent and irregular (i.e., occur any time of day) emissions that average 1 g/s for any three hours during the day, every day of the year.

  In this situation, the appropriate approach would be to input 0.125 g/s for each of the twenty-four hours in a day. This pattern would be applicable to every day in the year and there is no need to use variable emissions input tool for this type of situation.

  Where, emissions input for every hour = 1 g/s × (3 hours ⁄ 24 hours) = 0.125 g/s

Example 2.3c: Intermittent and Irregular (i.e., any time of day) Emissions; Only Two Days per Week

• Source with intermittent and irregular (i.e., occur any time of day) emissions that average 1 g/s for any three hours during the day and only two days per week.

  In this situation, the appropriate approach would be to input 0.036 g/s for each of the twenty-four hours. This pattern would be applicable to every day in the year.

  Where, emissions input for every hour = 1 g/s × (3 hours ⁄ 24 hours) x (2 days ⁄ 7 days) = 0.036 g/s

Example 2.3d: Intermittent and Regular (ie., same time of day) Emissions; Only for the Same Two Months Every Year

• Source with intermittent and regular emissions that average 1 g/s for any twenty- four hours per day but only for the same two months per year (i.e., zero emissions, other months).

In this situation, the appropriate approach would be to use the variable emissions tool and input 1 g/s for all 24-hours but only for the two months of emissions and 0 g/s for all other months in the year.