# Comparative Impacts of Freight and Non-truck Traffic on NO x and Ozone Concentrations in the Los Angeles Basin

## TL;DR

The study finds freight traffic contributes significantly to NOx and ozone levels in Los Angeles, with machine learning used to analyze pollution sources.

## Contribution

Applies random forest machine learning to estimate freight traffic's impact on NOx and ozone in Los Angeles.

## Key findings

- Freight activity contributes over half of weekday NOx impacts compared to non-truck traffic.
- Coastal and downwind areas in LA are VOC-limited during peak ozone hours.
- Los Angeles urban core remains in a VOC-limited regime for ozone production in summer.

## Abstract

The Los Angeles (LA) metropolitan region remains in nonattainment
for ozone despite decades of reductions of ozone precursors, nitrogen
oxides (NO
x
) and volatile organic compounds
(VOCs). NO
x
emissions from freight vehicles
(ships, heavy duty trucks, trains, and airplanes) are expected to
exceed emissions from passenger vehicles in southern California by
2030. Here, we use random forest machine learning to estimate the
impact of freight activity on hourly NO
x
concentrations and determine summertime ozone production regimes
across the LA basin. We find that freight activity contributes over
half of weekday NO
x
impacts relative to
non-truck traffic. During peak ozone hours, coastal areas, south LA,
areas downwind (east) of downtown LA, and downtown San Bernardino
are VOC-limited. Our results suggest that as of 2021, the Los Angeles
urban core and nearby downwind areas have not transitioned to a NO
x
-limited regime on most days during the May
to September ozone season. This study shows the applicability of machine
learning to estimate concentration impacts from specific sources in
the face of uncertain emission inventories and to analyze current
ozone production regimes in areas with hourly ground observations.