This README file describes the dataset accompanying the manuscript "Reductions in California's urban fossil fuel CO2 emissions during the COVID-19 pandemic" In review at AGU Advances, 2022 Corresponding authors: Cindy Yanez (ccyanez@uci.edu) and Claudia Czimczik (czimczik@uci.edu) Description of data: ----------------------------------------------------------------------------------------------------------------------- (1) CO2 Description: This folder contains .csv files for each set of mobile surveys conducted in the Los Angeles area. Data is combined from three instruments: Picarro G2401 analyzer, Garmin GPS, and METSEN500 weather sensor. All data was collected on July weekdays. Included files: a. LA2019_CO2xs.csv b. LA2020_CO2xs.csv c. LA2021_CO2xs.csv Data was processed as follows: - corrected time offsets between the instruments to cell phone clock time - applied quality control filters to Picarro G2401 data following the same protocol as Verhulst et al. (2017) - two-point linear correction to CO2 data based on standard gas calibration runs before and after each survey - average all measurements into 5 second intervals - grid data into consecutive 100 meter road segments - calculate urban CO2 enhancements ("CO2xs") by substracting a background that was characterized by flask data from Cape Kumukahi, Hawaii (Dlugokencky et al., 2021) - 2019 and 2021 data were filtered to only include observations that spatially overlapped with 2020 data - subset only measurements collected on freeways - subset only measurements collected between 11 AM to 4PM (local time) The variables included are: - Timestamp in UTC timezone - Latitude in decimal degrees north - Longitude in decimal degrees east - Altitude in meters - Speed in knots - Course in degrees - WS_avg (windspeed) in m/s - WindDir_vct (wind direction) in degrees - BarPressure (barometric pressure) in hPa - RelHumidity (relative humidity) in % - AirTemp_Avg (average air temperature) in degrees celsius - DewPoint in degrees celsius - CO2: carbon dioxide mole fraction (ppm) - CO2xs: carbon dioxide mole fraction enhancement over background (ppm) More information about calibration correction coefficients, sampling dates, and measurement precision are available in the manuscript Table S1. ----------------------------------------------------------------------------------------------------------------------- (2) C14 Description: This folder contains radiocarbon values of California annual grass species collected in 2020 and 2021. Radiocarbon values are reported here in two ways (1) the fraction modern notation, which does not change with time and (2) the Delta 14C notation, which represents the absolute amount of radiocarbon at the time it was measured. This notation was used for all analyses in the manuscript. These notations are described in detail in Trumbore et al. (2016) Included files plants_C14.csv The variables included are: - UCIAMS_ID: sample identification number - GENUS - SPECIES (if identifiable) - STATUS at time of collection (green or senesced) - LATITUDE in decimal degrees north - LONGITUDE in decimal degrees east - COLLECTION_DATE - FRACTIONMODERN: fraction modern - FM_ERR: measurement uncertainty in fraction modern - DEL14: radiocarbon content in the delta 14C notation in units of per mil - DEL14C_ERR: measurement uncertainty of DEL14C in units per mil - NEARESTCITY based on proximity to legal boundaries defined by the U.S. Census Bureau - COUNTY - REGION categorized using the same classification system as CEMA (2012), a state report that designated ten California regions based on the geographic, demographic and environmental characteristics of each county ----------------------------------------------------------------------------------------------------------------------- References: California Emergency Management Agency [CEMA]. (2012). California Adaptation Planning Guide: Understanding Regional Characteristics. Retrieved from https://resources.ca.gov/CNRALegacyFiles/docs/climate/APG_Understanding_Regional_Characteristics.pdf. Dlugokencky, E.J., J.W. Mund, A.M. Crotwell, M.J. Crotwell, and K.W. Thoning (2021), Atmospheric Carbon Dioxide Dry Air Mole Fractions from the NOAA GML Carbon Cycle Cooperative Global Air Sampling Network, 1968-2020, Version: 2021-07-30, https://doi.org/10.15138/wkgj-f215 Trumbore, S. E., Sierra, C. A., & Hicks Pries, C. E. (2016). Radiocarbon Nomenclature, Theory, Models, and Interpretation: Measuring Age, Determining Cycling Rates, and Tracing Source Pools. In E. A. G. Schuur, E. Druffel, & S. E. Trumbore (Eds.), Radiocarbon and Climate Change: Mechanisms, Applications and Laboratory Techniques (pp. 45–82). Springer International Publishing. https://doi.org/10.1007/978-3-319-25643-6_3 Verhulst, K. R., Karion, A., Kim, J., Salameh, P. K., Keeling, R. F., Newman, S., Miller, J., Sloop, C., Pongetti, T., Rao, P., Wong, C., Hopkins, F. M., Yadav, V., Weiss, R. F., Duren, R. M., & Miller, C. E. (2017). Carbon dioxide and methane measurements from the Los Angeles Megacity Carbon Project–Part 1: calibration, urban enhancements, and uncertainty estimates. Atmospheric chemistry and physics, 17(13), 8313-8341.