How Does FTIR Compare to Traditional Wet Testing Methods?

August 9, 2021

By: Shane Watton

There are two types of methods for measuring stack emissions – instrumental and the traditional wet chemistry method. With instrumental methods, such as those that use our extractive Fourier Transform Infrared Spectrometer (often referred to as FTIR), users will receive continuous real-time data onsite with data points obtained by the minute. Traditional wet methods provide only three composite data points throughout a typical compliance testing survey.  The wait for analytical data, which is required to determine pollutant emissions, can be two or three weeks.

Below are some factors that should be considered when comparing FTIR to wet methods.


The cost of using FTIR for emissions testing may be more expensive than the traditional wet method when looking for a single compound, however the cost savings come into play when looking at multiple compounds at once. For example, a traditional wet method for NOx, NH3, CO and SO2 would require 4 different tests with multiple samples, while the FTIR could detect all 4 of those compounds using one single test method. Sampling with the FTIR could also cut down on sampling time if multiple compounds are combined into one test, and typically FTIR sampling requires less personnel and equipment on site to perform these tests.

Having access to real-time data also provides great value to our clients. Data collected from the FTIR can be immediately relayed to our clients for compliance purposes or process troubleshooting. Before the Montrose field team departs the field site, our clients would know whether or not their source is within compliance approval limits.  Having live data can help our clients better understand their process. Even though the field team may only be looking for one or two compounds for compliance purposes, the spectra generated from the FTIR can detect several different compounds, which can provide great insight as to what is happening in the process.

The ability of the FTIR to obtain continuous real-time data of compounds during process modifications is another big advantage. This feedback helps companies make quick and money-saving decisions that can optimize their processes and reduce pollutant emissions.


Our team has multiple FTIR instruments, so we can quickly help numerous clients at one time. The FTIR and sampling can be set up and be ready to sample within a day of the sampling team arriving on the job site. Montrose has extensive knowledge of this instrument as we’ve completed thousands of FTIR-related projects in the U.S. and Canada.


To collect the data and adhere to quality assurance, FTIR follows these promulgated test methods:

  • US EPA Method 318 – Extractive FTIR Method for Measurement of Emissions from the Mineral Wool and Wool Fiberglass Industries
  • US EPA Method 320 – Vapor Phase Organic and Inorganic Emissions by Extractive FTIR
  • US EPA Method 321 – Gaseous Hydrogen Chloride Emissions at Portland Cement Kilns by FTIR

ASTM D6348 – Standard Test Method for Determination of Gaseous Compounds by Extractive Direct Interface Fourier Transform Infrared (FTIR) Spectroscopy

Have any additional FTIR questions? Feel free to reach out to our team anytime.

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