What is the purpose of EPA Method 5 in PM stack sampling?

• A. To measure gas temperature.
• B. To calibrate flow rate.
• C. To monitor humidity.
• D. To collect representative PM emissions from stack gases on filters for gravimetric determination and comparison with emission limits.

Answer: (D)

The main idea is to quantify particulate emissions by actually capturing a representative portion of the stack gas on a filter so you can measure how much dust is present and compare it to allowed limits. EPA Method 5 is designed to do this with a gravimetric approach, meaning you weigh the particulate collected on a filter.

To get a true picture of what’s being emitted, the sampling train is operated so that the gas drawn into the probe is isokinetic—the gas velocity in the stack matches the velocity at the sampling point. This helps ensure that particles aren’t skimmed away or overrepresented in the sample, especially the larger particles that would otherwise be biased by faster or slower sampling. The stack gas is drawn through a filter (and related hardware) so particulates collect on the filter media. Before and after sampling, the filter is conditioned and weighed in a controlled environment, and the difference in mass gives the mass of particulates collected. By recording the volume of gas that passed through the filter, you can calculate the emission concentration (mass per volume) and then compare it to the regulatory emission limits.

This method is specifically about collecting representative PM from stack gases on filters for gravimetric determination and regulatory compliance assessment. It isn’t about measuring gas temperature, calibrating flow rate in isolation, or monitoring humidity as the primary purpose.