What Is Source Testing? A Guide for Industrial Facility Managers

Source testing is the direct measurement of pollutant concentrations and emission rates at the point where they leave your equipment. A probe goes into the stack or duct, samples are collected under controlled conditions, and the results tell you exactly what your facility is emitting.

It is not ambient air monitoring. It is not a model or an estimate. Source testing gives you hard numbers from your specific equipment under your actual operating conditions.

If you manage a facility with permitted emission sources in Southern California, SCAQMD and CARB require source testing to verify compliance. This post walks through the full process: what gets tested, why it is required, who performs it, and what to expect from start to finish.

Source Testing vs. Ambient Monitoring

These two are often confused. Source testing measures pollutant concentrations directly at the emission point, inside the stack or duct. Results are expressed in concentrations (ppm) and mass emission rates (lb/hr, lb/day). Ambient monitoring measures concentrations in the surrounding air. It tells you regional air quality, not which specific source is responsible.

SCAQMD uses both. But as a facility manager, source testing is your compliance obligation.

Why Source Testing Is Required

SCAQMD issues operating permits with specific emission limits. Source testing proves your equipment meets those limits. The regulatory drivers include:

• Permit compliance: Your permit conditions specify testing frequencies and parameters. Failure to test on schedule is a standalone violation.
• Rule-specific requirements: Rule 1146 and Rule 1147 cover boilers, process heaters, and miscellaneous combustion sources. Rules 218.2 and 218.3 govern CEMS certification.
• CARB and EPA requirements: Title V major sources, NSPS equipment, and NESHAPs regulated units have additional federal and state testing obligations.
• RECLAIM transition: Former RECLAIM facilities must now source test individual units to demonstrate BARCT compliance under landing rules (1135, 1109.1, 1134).

What Gets Measured

Source testing can measure virtually any air pollutant. The specific pollutants tested at your facility depend on your permit conditions and applicable rules.

Criteria Pollutants

These are the pollutants regulated under the National Ambient Air Quality Standards:

• NOx (nitrogen oxides): The primary pollutant of concern for combustion sources in the South Coast Air Basin. Measured using SCAQMD Method 100.1 or CARB Method 100.
• CO (carbon monoxide): Typically tested alongside NOx for combustion sources. Measured using SCAQMD Method 100.1 or CARB Method 100.
• SO2 (sulfur dioxide): Required when burning fuels with sulfur content. Measured using SCAQMD Method 100.1, SCAQMD Method 6.1, or CARB Method 100.
• PM/PM10/PM2.5 (particulate matter): Measured using SCAQMD Methods 5.1–5.3, EPA Method 5 (total PM), Method 201A (PM10/PM2.5 with cyclone), or Method 202 (condensable PM).
• VOC (volatile organic compounds): Measured using SCAQMD Method 25.1/25.3, EPA Method 25A, or Method 18 (individual organic compounds by GC).

Air Toxics

For facilities with toxic air contaminant requirements:

• Metals (lead, chromium, nickel, arsenic, etc.): Measured using CARB Method 436.
• Formaldehyde: Measured using CARB Method 430.
• Dioxins and furans: Measured using CARB Method 428.
• Hydrogen chloride (HCl): Measured using CARB Method 421.
• Hexavalent chromium: Measured using CARB Method 425.

Stack Parameters

Source testing also measures auxiliary stack parameters: velocity and flow rate (SCAQMD Method 2.1–2.3), moisture (SCAQMD Method 4.1), O2/CO2 (SCAQMD Method 100.1), and temperature. These measurements convert raw concentration data into mass emission rates for comparison against permit limits.

Who Performs Source Testing

In California, source testing for regulatory compliance must be performed by a company certified under the Laboratory Approval Program (LAP), administered jointly by CARB and the local air districts. LAP certification requires demonstrated competency in each test method, properly calibrated equipment, qualified personnel, QA/QC procedures, and successful proficiency audits.

Using a non-LAP-approved firm means your results will not be accepted by SCAQMD. You will need to retest with an approved firm, doubling your cost and potentially missing your compliance deadline.

The Source Testing Process: Step by Step

A source test is not a single event. It is a multi-step process that spans several weeks from initiation to final report.

Step 1: Scope and Planning

The testing company reviews your permit conditions, identifies the required test methods and pollutant parameters, and evaluates your stack or duct sampling locations. If you do not have existing sample ports, they may need to be installed.

Sample port locations must meet SCAQMD Method 1.1–1.2 criteria for upstream and downstream distances from flow disturbances. Poor port locations produce unrepresentative data.

Step 2: Protocol Preparation and Submission

A test protocol is prepared and submitted to SCAQMD for approval. The protocol details:

• Equipment to be tested and permit numbers
• Pollutants and test methods
• Sampling locations
• Normal operating conditions during testing
• QA/QC procedures
• Testing schedule

SCAQMD typically requires 30 to 45 days to review and approve a protocol. They may request modifications. Plan accordingly.

Step 3: Pre-Test Coordination

Once the protocol is approved, the testing company coordinates with your operations team on scheduling, utility connections, and safe access to sampling locations. Your equipment must run at the specified conditions on your permit during the test. Running at reduced capacity to produce lower emissions is a protocol violation and will invalidate the results.

Step 4: On-Site Testing

The testing crew arrives with sampling equipment, sets up at the designated sampling locations, and conducts the test.

On-site duration depends on complexity:

• Simple combustion source (NOx, CO only): 1 day on-site.
• PM testing (Method 5): 1 day on-site. We can set up and test on the same day. Each run requires isokinetic sampling, plus setup and breakdown time.
• Metal testing: 2 to 3 days on-site (three consecutive runs of 4 or 8 hours each, most often 8 hours). Other pollutants can be completed simultaneously in a single day, which gives our crews a scheduling advantage.

During testing, the crew collects real-time data and field samples. Our crew will collect this process data (fuel flow, load, temperatures) for the test report while your operations staff maintains specified operations.

Step 5: Data Reduction and Analysis

After on-site work, the testing company processes raw data: laboratory analysis of collected samples, calculation of emission concentrations and mass rates, correction to standard conditions (dry basis, reference O2), and comparison against permit limits. Data reduction typically takes 2 to 4 weeks.

Step 6: Final Report

The completed report is submitted to SCAQMD within the 30-calendar-day deadline. It includes all raw data, calculations, QA/QC documentation, process operating data, and a clear statement of compliance or non-compliance for each pollutant tested.

If any results exceed permit limits, the report must note the exceedance. Your facility will need to take corrective action and retest.

How Long the Entire Process Takes

From initial contact to final report submission, budget 8 to 12 weeks:

• Protocol preparation: 1 to 2 weeks
• SCAQMD protocol review: 4 to 6 weeks
• Pre-test coordination: 1 week
• On-site testing: 1 to 3 days
• Data reduction and report preparation: 2 to 4 weeks

Do not wait until your testing deadline is 30 days out. By the time the protocol is approved, you will already be past due.

Frequently Asked Questions