The Hestia Fossil Fuel CO<sub>2</sub> Emissions Data Product for the Los Angeles Megacity (Hestia-LA)

Abstract. As a critical constraint to atmospheric CO2 inversion studies, bottom-up spatiotemporally-explicit emissions data products are necessary to construct comprehensive CO2 emission information systems useful for trend detection and emissions verification. High-resolution bottom-up estimation is also useful as a guide to mitigation options, offering details that can increase mitigation efficiency and synergize with other policy goals at the national to sub-urban spatial scale. The ‘Hestia Project’ is an effort to provide bottom-up fossil fuel (FFCO2) emissions at the urban scale with building/street and hourly space-time resolution. Here, we report on the latest urban area for which a Hestia estimate has been completed – the Los Angeles Megacity, encompassing five counties: Los Angeles County, Orange County, Riverside County, San Bernardino County and Ventura County. We provide a complete description of the methods used to build the Hestia FFCO2 emissions data product which is presented on a 1 km x 1 km grid for the years 2010–2015. We find that the LA Basin emits 48.06 (± 5.3) MtC/yr, dominated by the onroad sector. Because of the uneven spatial distribution of emissions, 10 % of the largest emitting gridcells account for 93.6 %, 73.4 %, 66.2 %, and 45.3 % of the industrial, commercial, onroad, and residential sector emissions, respectively. Hestia FFCO2 emissions are 10.7 % larger than the inventory estimate generated by the local metropolitan planning agency, a difference that is driven by the industrial and electricity production sectors. The Hestia-LA v2.5 emissions data product can be downloaded from the data repository at the National Institute of Standards and Technology (https://doi.org/10.18434/T4/1502503).