Characterizing the near-road NO_x gradient for exposure assessment purposes

Area of Science:

• Environmental Science
• Public Health
• Atmospheric Chemistry

Background:

• 24% of the US population lived near high-volume roadways in 2020.
• Roadways are significant sources of nitrogen oxides (NOx) and nitrogen dioxide (NO2) emissions.
• Understanding near-road air pollution gradients is crucial for assessing community exposure.

Purpose of the Study:

• To synthesize existing literature on NOx and NO2 concentration gradients in near-road environments.
• To identify factors influencing these pollutant gradients.
• To quantify community exposure to near-road air pollution.

Main Methods:

• Systematic literature search using US EPA methods.
• Synthesis and summarization of near-road decay gradients for NO2 and NOx.
• Analysis of concentrations, distance, and impacting variables using visual and regression methods.

Main Results:

• NOx and NO2 concentrations decrease non-linearly with distance from roadways.
• Steepest decline in concentrations occurs within 50m of roadways.
• Pollutant levels typically reach background concentrations by 500m.
• Concentrations increase with cooler temperatures and higher traffic volumes.

Conclusions:

• Near-road population exposure to NOx and NO2 is influenced by distance and other variables.
• Distance from the roadway is the primary driver of the pollutant gradient.
• This review quantifies key variables impacting near-road air pollution exposure.