A fuel-based method for updating mobile source emissions during the COVID-19 pandemic

Abstract

The COVID-19 pandemic and ensuing lockdown of many US States resulted in rapid changes to motor vehicle traffic and their associated emissions. This presents a challenge for air quality modelling and forecasting during this period, in that transportation emission inventories need to be updated in near real-time. Here, we update the previously developed fuel-based inventory of vehicle emissions (FIVE) to account for changes due to COVID-19 lockdowns. We first construct a 2020 business-as-usual (BAU) case inventory and adjust the emissions for a COVID-19 case using monthly fuel sales information. We evaluate cellular phone-based mobility data products (Google COVID-19 Community Mobility, Apple COVID-19 Mobility Trends) in comparison to embedded traffic monitoring sites in four US cities. We find that mobility datasets tend to overestimate traffic reductions in April 2020 (i.e. lockdown period), while fuel sales adjustments are more similar to changes observed by traffic monitors; for example, mobility-based methods for scaling emissions result in an approximately two-times greater estimate of on-road nitrogen oxide (NO x ) reductions in April 2020 than we find using a fuel-based method. Overall, FIVE estimates a 20%–25% reduction in mobile source NO x emissions in April 2020 versus BAU, and a smaller 6%–7% drop by July. Reductions in April showed considerable spatial heterogeneity, ranging from 6% to 39% at the state level. Similar decreases are found for carbon monoxide (CO) and volatile organic compounds. Decreases to mobile source NO x emissions are expected to lower total US anthropogenic emissions by 9%–12% and 3%–4% in April and July, respectively, with larger relative impacts in urban areas. Changes to diurnal and day-of-week patterns of light- and heavy-duty vehicular traffic are evaluated and found to be relatively minor. Beyond the applicability to modelling air quality in 2020, this work also represents a methodology for quickly updating US transportation inventories and for calibrating mobility-based estimates of emissions.

Space‐Based Observational Constraints on NO2 Air Pollution Inequality From Diesel Traffic in Major US Cities

“…The Fuel-based Inventory from Vehicle Emissions (FIVE18-19) is a US-wide, 4 × 4 km 2 mobile source (onroad and off-road, gasoline and diesel engines) NO x emissions inventory providing monthly mean hourly data on weekdays, Saturdays, and Sundays (Harkins et al, 2021;McDonald et al, 2012McDonald et al, , 2018. Emission rates are based on publicly available fuel sales reports, road-level traffic counts, and time-resolved weigh-inmotion traffic counts.…”

Assessment of Updated Fuel‐Based Emissions Inventories Over the Contiguous United States Using TROPOMI NO2 Retrievals

“…FIVE was shown to improve model predictions of NO x and O 3 when compared to the NEI (McDonald et al, 2014). The FIVE inventory has been updated from 2018 through the end of 2020, including the period of the COVID-19 pandemic (Harkins et al, 2021). Here, we use the FIVE emissions for 2018 (denoted FIVE18) in the baseline simulations.…”

“…To support NOAA air quality forecasting efforts, the Fuel-based Inventory of Vehicle Emissions (FIVEs) have been developed for mobile source engines and implemented in the Weather Research and Forecasting with Chemistry (WRF-Chem) model (Kim et al, 2016;McDonald et al, 2018) and has been implemented in the Rapid Refresh with Chemistry (RAP-Chem) forecast model (https://rapidrefresh.noaa.gov/RAPchem/). Recently, the FIVE inventory has been updated through the end of 2020 and captures changes through the COVID-19 pandemic (Harkins et al, 2021). In this study, we focus on evaluations of FIVE with TROPOMI NO 2 data from 2018, leveraging prior modeling by the NOAA Chemical Sciences Laboratory performed for the Long Island Sound Tropospheric Ozone Study (LISTOS) (Coggon et al, 2021).…”

COVID‐19 Induced Fingerprints of a New Normal Urban Air Quality in the United States

“…For the BAU case, we account for typical seasonal and day-of-week activity patterns of light-and heavy-duty vehicles separately. For the COV-ID-19 case, we scale the January BAU emissions case with real-time light-and heavy-duty vehicle traffic counting data for the year 2020, which are described in Harkins et al (2021). Light-duty vehicle counts are used to project on-road gasoline emissions and heavy-duty truck counts for on-road diesel emissions during the pandemic.…”