Estimating emissions from stationary diesel engines (i.e., diesel compression ignition engines) presents unique challenges related to assessing Diesel Particulate Matter (DPM) and the other Toxic Air Contaminants (TACs) present in these emissions. DPM is an aggregate pollutant, meaning that it is comprised of a number of chemical compounds including black carbon (soot) and multiple incomplete combustion byproducts; it also contains metal and Polycyclic Aromatic Hydrocarbon (PAH) TACs in variable quantities. Diesel Particulate Matter emissions
DPM emissions must be included in the toxic emission inventory from diesel generators. In Oregon, source testing for particulate matter using DEQ Method 5 requires sampling of both the filterable (“front half") and condensable (“back half") Particulate Matter (PM) from an emissions source. Therefore, DEQ recommends including both the filterable and condensable PM when establishing an emission factor for risk assessment purposes. For newer Tier 2 federally compliant diesel engines still under manufacturer warranty, DEQ has approved the use of manufacturer emissions data for PM for the filterable fraction, and use of Hydrocarbon (HC) data as a conservative surrogate for the condensable fraction. For older engines a more conservative emissions factor may be required.Toxic air contaminant emissions other than diesel particulate matter
Because of the compositional variability of DPM emissions, DEQ requires facilities to report emissions of DPM as well as emissions for all other TACs listed in OAR 340-245-8020 Table 2 for which emission factor data are available. Below is a table of recommended TAC emission factors for diesel internal combustion operations – these factors may represent conservative over-estimates of emissions from Tier 2 engines as they are based on testing performed before Tier 1 federal performance standards were implemented. These emissions data were taken from Ventura County Air Pollution Control District and South Coast Air Quality Management District AB 2588 reporting documents.
Toxic Air Contaminant|
|7440-43-9||Cadmium and compounds||0.0015|
|1854-02-99||Chromium VI, chromate, and dichromate particulate||0.0001|
|7440-38-2||Arsenic and compounds||0.0016|
|7439-92-1||Lead and compounds||0.0083|
|7440-02-0||Nickel and compounds||0.0039|
|-||PAHs (excluding Naphthalene)||0.0362|
|50-32-8||Benzo[a]pyrene||3.55 x 10-5|
|7440-50-8||Copper and compounds||0.0041|
|7439-96-5||Manganese and compounds||0.0031|
|7439-97-6||Mercury and compounds||0.002|
|7782-49-2||Selenium and compounds||0.0022|
|1330-20-7||Xylene (mixture), including m-xylene, o-xylene, p-xylene||0.0424|
|-||Diesel Particulate Matter||See DPM section|
 – Benzo[a]pyrene emission factor is derived from AP-42 Table 3.4-4 value using 138,000 BTU/gallon of diesel. These emissions are required to account for Noncancer health impacts – see below.Noncancer health effects from Benzo[a]pyrene
 – Ammonia value corresponds to equipment with Selective Non-Catalytic Reduction (SNCR) control; for equipment with Selective Catalytic Reduction (SCR) control substitute 1.4 lb/M gal, and for equipment without SNCR or SCR substitute 0.8 lb/M gal.
In cases where facilities have reported PAH emissions in aggregate (as in the above table), DEQ has required benzo[a]pyrene emissions to be accounted for separately in order to capture noncancer health effects, both chronic and acute, of this TAC in the risk assessment. This is because the aggregate PAH Risk Based Concentration (RBC) in OAR 340-245-8040 Table 4 only accounts for the cancer health effects.Cold start emissions
Diesel emergency generators have higher emissions at start up (creating a 'black puff'). DEQ recommends using data on transient cold start emissions included in Section 3.4 (p.31) of this report on emissions from stationary diesel engines prepared by the California Energy Commission to develop TAC emissions from cold starts. These emissions should account for the transient increase in DPM and organic species present from incomplete combustion. Metals emissions should remain unaffected during this period. Please provide documentation on the methodology and assumed number of cold starts anticipated per emergency generator on both an annual and acute basis.Operational considerations for modeling emissions from diesel engines influencing EF values
Emissions from diesel engines should be modeled based on fuel consumption because all of the TAC emission factors are based on pounds per thousand gallons of fuel used. DEQ has approved approaches that assume the worst-case manufacturer data for PM and HCs relative to engine loading, coupled with the highest fuel consumption rate (i.e., typically 100% load). In this way, the facility ensures that the modeled risk, and subsequent risk assessment, provides a worst-case scenario.
In general, DEQ recommends that facilities take a more conservative approach to estimating emissions from these TEUs as in many cases the emission factors and rates used to model risk from a facility will become enforceable limits in their permits. For facilities that have a large number of generators, DEQ may require source test validation of these emission factors and rates.
Modeling decisions about diesel engine operations should be made in conjunction with submitting the emissions inventory as they are critical for determining the DPM emission factor values used in the risk assessment.