The COVID-19 pandemic is impacting human activities, and in turn energy use and carbon dioxide (CO₂) emissions. Here we present daily estimates of country-level CO₂ emissions for different sectors based on near-real-time activity data. The key result is an abrupt 8.8% decrease in global CO₂ emissions (−1551 Mt CO₂) in the first half of 2020 compared to the same period in 2019. The magnitude of this decrease is larger than during previous economic downturns or World War II. The timing of emissions decreases corresponds to lockdown measures in each country. By July 1st, the pandemic’s effects on global emissions diminished as lockdown restrictions relaxed and some economic activities restarted, especially in China and several European countries, but substantial differences persist between countries, with continuing emission declines in the U.S. where coronavirus cases are still increasing substantially.

A Correction to this paper has been published: https://doi.org/10.1038/s41467-020-20254-5

Fossil fuel (FF) burning, the main energy source of the modern world’s economy, remains the major source of anthropogenic carbon dioxide (CO₂) and pollutants in the atmosphere. Based on 18 years (2001–2018) of aerosol optical depth (AOD) data from Moderate Resolution Imaging Spectroradiometer satellite, FFCO₂ emissions from the Open-Data Inventory for Anthropogenic Carbon dioxide, and gross domestic product (GDP) data from the World Bank, we found that air quality, FF consumption, and economy are strongly bonded at the continental scale but decoupled at the national level under favorable policies. The comparison of AOD vs PM_2.5 and NO₂ over urbanized areas shows that the pollutants leading to the AOD load can vary significantly by country. A strong connection between GDP and FFCO₂ emissions indicates that economic growth deeply replies on FF consumption in most countries. Meanwhile, air pollution is more associated with the growing trend than the level of development of a country. With more mature technologies and renewable energy, economies can keep growing without compromising their environment and population health.

Fire emissions from Mexico and Central America are transported regularly to the U.S. Gulf Coast every spring under prevailing circulation patterns and affect U.S. air quality. Here we use a GEOS‐Chem passive tracer simulation to develop the climatology of transport pathways of fire emissions over a long‐term time period of April and May 2002–2015 and estimate their adverse air quality effects for urban areas along the Gulf Coast. A conceptual model is presented to describe the transport mechanisms, which involve southerly low‐level jets in the lower troposphere and warm conveyor belt in the middle troposphere. The warm conveyor belts and the southerly low‐level jets explain 31% and 69% of the interannual variability of the mid‐altitude (1.5–6 km) and low‐altitude events (0–1.5 km), respectively. Considering both transport and fire emissions, approximately 9% of the study period (59–88 days of 854 days) were identified as large pollution events during which Central American fire emissions adversely impacted surface air quality at several major urban centers along the Gulf Coast, including Houston and Corpus Christi in TX, New Orleans in LA, Mobile in AL, and Pensacola in FL. Compared to clean maritime flow from the Gulf of Mexico, these events were estimated to result in average enhancements of maximum daily average 8‐hr (MDA8) ozone and daily PM_2.5 (fine particulate matter <2.5 μm in diameter) in the Gulf Coast cities of 3–12 ppbv and 2–5 μg/m³, respectively. Only one ozone exceedance day (79 ppbv, on 18 May 2003) was found among the fire‐impact days for the Houston region.

We investigated the impacts of cold fronts on area-wide peak O₃ and regional background O₃ mixing ratios on a daily scale over the Houston-Galveston-Brazoria (HGB) area of southeastern Texas during the O₃ seasons (April–October) of 2003–2016. Back trajectories showed that an 18h time lag existed between arrival of cold fronts in the HGB area and onset of a predominately northerly flow. Cold fronts showed increasing effects on both peak and background O₃ over the HGB area. Compared to no front days, average peak O₃ mixing ratios during the cold front 1st days, cold front 2+ days, and post frontal days increased 0.7, 5.9, and 9.0 ppbv, respectively while average background O₃ increased 2.9, 6.8, and 8.6 ppbv, respectively. The change in wind direction from southerly to northerly was the most important factor causing increasing O₃ levels. Wind direction shifts caused variation of other meteorological factors (i.e., wind speed, precipitation, temperature, cloud cover, and relative humidity) and tended to overshadow their effects on O₃ over the HGB area. On a long-term and large-scale view, cold fronts over the HGB area could be regarded as interruptions in the cleansing effects of predominantly marine southerly flow from the Gulf of Mexico.