Do diesel generators, boilers and other stacks need emission testing?

Exceeding point source emission standards is prohibited. A source must meet the industry-specific standards in Appendix 4, and the general standards in Appendix 3 for any pollutant that Appendix 4 does not cover.^{1Air reg. Art. 5, First (1)}

The Appendix 3 general standards include:^{2Air reg. Appendix 3}

The opacity limit is written as 'should not exceed 20% of the normal level'. The regulation does not explain what 'normal level' means.^{3Air reg. Appendix 3, item 1}

Compliance with Appendix 4 is judged against hourly average data unless stated otherwise, corrected to standard conditions as specified by USEPA methods.^{7Air reg. Appendix 4, Note (1)}

Appendix 4 has separate rows for combustion facilities built before 1 September 2005 (row 12) and those built or modified after that date (row 13).^{8Air reg. Appendix 4, rows 12 and 13}

For facilities built or modified after 1 September 2005, the limits include:^{9Air reg. Appendix 4, row 13}

Each gas turbine class also has an SO2 limit of 0.015 percent by volume at 15 percent O2 and a turbine fuel sulphur limit below 0.8 percent by weight.^{11Air reg. Appendix 4, rows 13.14 to 13.22}

For mixed fuels, the standard is prorated by the share of heat input from each fuel.^{12Air reg. Appendix 4, Note (6)}

Row 12.10, a 43 ng/J particulate limit for small units built before 2005, carries a reviewer comment in the published English text reading 'Not in the standards'. Its status is unclear.^{13Air reg. Appendix 4, row 12.10}

The regulation contains no emission standard written specifically for diesel generators or reciprocating engines. The combustion rows in Appendix 4 cover steam generating units, furnaces, gas turbines and duct burners.^{8Air reg. Appendix 4, rows 12 and 13}

Appendix 4 states that general standards apply to all emission sources unless individual facility standards are specified.^{14Air reg. Appendix 4, Note (2)}

Read together, these provisions point to the Appendix 3 general standards for a generator, including the 20 percent opacity limit. The regulation does not state this for generators in so many words.^{3Air reg. Appendix 3, item 1}

The annual testing duty applies to point sources not subject to continuous monitoring and covers all their stacks. The regulation does not mention standby or emergency generators and does not exempt them.^{15Air reg. Art. 5, Fourth (1)}

NCEC may set further requirements in permits, and breaching any air quality requirement it issues is fined 50,000 riyals per requirement.^{16Air reg. Table 3 (2024), item 37}

Sources listed in Appendix 5 must install NCEC-approved continuous emission monitoring. NCEC may also require it on other sources based on EIA, audit or inspection results.^{17Air reg. Art. 5, Third (1) and (2)}

Appendix 5 includes, among others:^{18Air reg. Appendix 5}

Combustion sources burning only natural gas or hydrogen are exempt from continuous monitoring of opacity and SO2.^{21Air reg. Appendix 5, Note (2)}

A source can be exempted from continuous NOx monitoring if a performance test and later spot tests show NOx consistently below 70 percent of the standard for facilities built after 1 September 2005. This needs consecutive spot tests: 2 results below 50 percent, 3 below 60 percent, 4 below 70 percent, or 30 days below 70 percent with a portable continuous monitor. The tests must be at least 3 months apart and completed within 2 years.^{22Air reg. Appendix 5, Note (3)}

Operators with continuous monitoring must:

Point sources without continuous monitoring must measure and analyse all their stack emissions every year for the primary pollutants in Appendices 3 and 4. NCEC may ask for additional measurements.^{28Air reg. Art. 5, Fourth (1) and (2)}

The main rules are:

A primary source is one with uncontrolled potential to emit more than 100 t/y of CO, NOx, SO2, PM or lead, more than 10 t/y of one hazardous organic air pollutant or 25 t/y combined, or any source burning hazardous material or waste.^{34Air reg. Art. 5, Fourth (5)}

For primary sources, NCEC must be notified 'within thirty (30) working days before' testing, and the results report is due within 40 working days of the test. The notice wording is ambiguous, and giving at least 30 working days of notice is the cautious reading.^{35Air reg. Art. 5, Fourth (8) and (10)}

The report for a primary source must include analytical and physical data, operating conditions during sampling, calculation methods, results and calibration data.^{36Air reg. Art. 5, Fourth (10)}

You must notify NCEC immediately of emergencies, start-up or shutdown that may breach point source emission standards.^{37Air reg. Art. 5, First (5)}

Table 1 of Article 5 exempts these cases from the emission standards:^{38Air reg. Art. 5, First (6)}

NCEC may verify that an emergency did not result from an environmental violation. Where exceedance continues for more than 6 hours it may take suitable measures, including approving or rejecting an extension.^{40Air reg. Art. 5, First (6) and (7)}

Records of start-ups, shutdowns, disruptions, failures, tests, calibration and maintenance must be kept for at least 5 years. NCEC may extend this by 5 years for some activities.^{41Air reg. Art. 5, Fifth (1)(a)}

If a source cannot meet a standard, the operator may apply for a temporary permit to exceed it. The technical study must include emission data, dispersion modelling, evidence that compliance is technically impossible, an economic analysis and an action plan with timelines and costs.^{42Air reg. Art. 5, Second (1) and (2)}

NCEC decides within 15 working days of registering the request, after collecting the study fees, and may extend this by 5 working days.^{43Air reg. Art. 5, Second (4)}

The fee ceiling for a permit to temporarily exceed point source emission standards is 11,000 riyals.^{44Fees reg. Appendix 1, item 53}

The permittee must submit periodic progress reports at the frequency NCEC sets.^{45Air reg. Art. 5, Second (7)}

Table 3 of the Air Quality regulation includes these fines for stacks and emission monitoring:^{46Air reg. Table 3 (2024)}

Not maintaining machinery and emission controls is fined 20,000 to 200,000 riyals, and not maintaining stacks 10,000 to 100,000 riyals.^{48Air reg. Table 3 (2024), items 9 and 12}

Serious violations are penalised in proportion to the damage, with the amount estimated by an expert committee formed by NCEC's CEO.^{49Air reg. Art. 8(2) and (3)}

A 1446H ministerial decision re-issued Table 3 without changing any amount. It classes every row as serious except row 11 (stacks not designed to the Article 6 controls, 50,000 riyals plus rectification), whose classification cell is blank.^{50Decision 15029057 (1446H), Air reg. Table 3 (2024), row 11}

These are the most common stack testing failures: