An air emission risk assessment of non-criteria pollutants in a tunnel study in Rio de Janeiro, Brazil.

Area of Science:

• Environmental Science
• Atmospheric Chemistry
• Transportation Engineering

Background:

• Brazil's unique ethanol-powered vehicle fleet presents distinct mobile source emission profiles.
• Tunnel investigations offer real-world vehicular conditions for accurate emission rate estimation, unlike standardized laboratory methods.

Purpose of the Study:

• To evaluate and compare two distinct methods for estimating emission factors from vehicles in the Rebouças Tunnel, Rio de Janeiro.
• To assess the emission rates of total aldehydes, BTEX compounds, and naphthalene from Brazil's circulating vehicle fleet.

Main Methods:

• Utilized two monitoring points in the L1 gallery of the Rebouças Tunnel over thirteen sampling campaigns between 2017 and 2020.
• Employed the Pierson correlation method and the fuel consumption testing method to estimate emission factors.
• Collected data on traffic flow, CO, and CO2 concentrations for method comparison.

Main Results:

• The Pierson method yielded total aldehyde emission rates of 22.1 ± 6.9 mg km⁻¹, while fuel consumption testing resulted in 17.7 ± 7.8 mg km⁻¹.
• Acetaldehyde was the predominant aldehyde. Benzene was the most abundant BTEX compound (3.7 ± 3.2 mg km⁻¹ via Pierson, 2.5 ± 0.3 mg km⁻¹ via fuel consumption).
• Naphthalene emission rates were 1.4 ± 1.0 mg km⁻¹ (Pierson) and 0.9 ± 0.4 mg km⁻¹ (fuel consumption).

Conclusions:

• Both the Pierson correlation and fuel consumption testing methods provide converging estimates for vehicle emissions, despite methodological differences.
• The selection of an emission estimation method should be guided by the availability of resources and specific study requirements.
• The Pierson method offers an alternative that bypasses the need for CO and CO2 measurements, relying instead on traffic flow data.