grey map covered with red and green patches of color

Investigation of Los Angeles Daily Traffic Patterns using TEMPO NO2 Data

Aline Maybank, Ella Xu

Abstract

Nitrogen dioxide (NO2) is a traffic-related air pollutant with known respiratory health effects. Urban NO2 levels vary by time of day and location due to traffic patterns and atmospheric conditions. This study uses data from NASA’s new TEMPO satellite to characterize weekday and weekend NO2 patterns in Los Angeles, a city with chronic air quality challenges and dense transportation infrastructure. Hourly Level 3 tropospheric NO2 data were downloaded from NASA EarthData for March 2-8, 2025. Using R (v2023.06.2), we processed satellite files, filtered to the Los Angeles metropolitan area, and conducted diurnal, spatial, and change detection analyses. Spatial averages and time- series plots were generated, and hotspot and change detection maps were constructed by comparing NO2 levels across three time blocks: 7-9 AM, 10 AM-12 PM, and 1-4 PM. NO₂ concentrations peaked sharply in the afternoon on March 2, reaching over 8×10¹⁴ molecules/cm², while other weekdays showed lower and more stable levels. Spatial mapping showed high morning NO2 concentrations along major freeways such as the 60 freeway, with reductions by midday. Hotspot analysis identified persistent NO2 elevations near high-traffic corridors. Change detection revealed weekday NO2 declines from morning to noon and increases from noon to afternoon in inland areas. In contrast, weekend patterns were more variable, with widespread afternoon increases. These findings underscore the utility of TEMPO data in capturing fine-scale NO2 dynamics and informing urban pollution management.

line graph of hourly no2 time series weekdays only

Figure 1. Hourly NO2 Time Series of Weekdays Only. Mean NO₂ concentrations (molecules/cm²) are plotted by hour for three weekdays: March 2, 6, and 7, 2025. March 6 is not included as the data was only available from 7–10 AM due to limited satellite coverage that day.

spatial distribution of no2 in los angeles

Figure 2. Spatial Distribution of NO2 in Los Angeles at 7 AM and 12 PM. Mean NO2 concentrations (molecules/cm2) are mapped across the Los Angeles region for A) 7 AM and B) 12 PM using TEMPO data from March 5–7, 2025. Road network overlays are sourced from OpenStreetMap.

openstreetmap of los angeles with red dots highlighting no2 hotspots

Figure 3. NO2 Hotspots in the Greater Los Angeles Area. Hotspots represent the top 5% of spatially averaged NO2 concentrations (molecules/cm2) calculated across all daytime hours for selected weekdays (March 2, 5–7, 2025).

change in no2 across periods of time in los angeles

Figure 4. Changes in NO2 across periods of time in Los Angeles and the surrounding metropolitan area, where (a) Morning to noon on weekdays, (b) Noon to afternoon on weekdays, (c) morning to noon on weekends, and (d) noon to afternoon on weekends. Green pixels represent an increase in NO2 with time, while red pixels indicate a decrease in NO2 with time. Yellow pixels show areas where NO2 stayed relatively constant.

table of 03/2-03/8

Table 1. Visual representation of data availability by day and hour for the temporal scale of this study. Green cells represent available and usable files, yellow cells represent available but corrupt files, and red cells represent unavailable files from the requested NASA EarthData download.