Emission Flux Measurement Error with a Mobile DOAS System and Application to NO_x Flux Observations

Area of Science:

• Environmental Science
• Atmospheric Chemistry
• Optical Remote Sensing

Background:

• Mobile differential optical absorption spectroscopy (DOAS) is a key technique for real-time measurement of trace gas emission flux from various pollution sources.
• Accurate flux measurements are often challenged by factors such as wind speed, wind direction, and the instrument's own velocity.
• Understanding and quantifying these influencing factors is crucial for reliable emission estimations.

Purpose of the Study:

• To conduct a detailed error analysis of mobile DOAS measurements for emission flux.
• To estimate nitrogen oxides (NOx) emissions from a power plant using mobile DOAS.
• To compare mobile DOAS results with data from a Continuous Emission Monitoring System (CEMS) to validate accuracy.

Main Methods:

• Utilized mobile DOAS to measure sulfur dioxide (SO₂) and nitrogen dioxide (NO₂) emission fluxes.
• Compared mobile DOAS data with CEMS data under varying drive velocities and wind field conditions.
• Analyzed uncertainties associated with column density, wind field data, and drive velocity.

Main Results:

• Identified optimal drive velocity for mobile DOAS measurements as 30-40 km/h.
• Determined that selecting wind field data at plume height is critical for accurate observations.
• Reported total errors for SO₂ and NO₂ emissions as 32% and 30%, respectively.
• Estimated NOx emission at 0.15 ± 0.06 kg/s, closely matching CEMS data (0.17 ± 0.07 kg/s).

Conclusions:

• Mobile DOAS is a valuable tool for assessing air pollution emissions from industrial sources.
• Optimizing operational parameters like drive velocity and wind field selection significantly enhances measurement accuracy.
• The study validates the reliability of mobile DOAS for emission monitoring and provides a foundation for improved estimation techniques.