The effects of the COVID-19 lockdowns on the composition of the troposphere as seen by In-service Aircraft for a Global Observing System (IAGOS) at Frankfurt

The European research infrastructure IAGOS (In-service Aircraft for a Global Observing System) equips commercial aircraft with a system for measuring atmospheric composition. A range of essential climate variables and air quality parameters are measured throughout the flight, from take-off to landing, giving high-resolution information in the vertical in the vicinity of international airports and in the upper troposphere–lower stratosphere during the cruise phase of the flight. Six airlines are currently involved in the programme, achieving a quasi-global coverage under normal circumstances. During the COVID-19 crisis, many airlines were forced to ground their fleets due to a fall in passenger numbers and imposed travel restrictions. Deutsche Lufthansa, a partner in IAGOS since 1994 was able to operate an IAGOS-equipped aircraft during the COVID-19 lockdown, providing regular measurements of ozone and carbon monoxide at Frankfurt Airport. The data form a snapshot of an unprecedented time in the 27-year time series. In May 2020, we see a 32 % increase in ozone near the surface with respect to a recent reference period, a magnitude similar to that of the 2003 heatwave. The anomaly in May is driven by an increase in ozone at nighttime which might be linked to the reduction in NO during the COVID-19 lockdowns. The anomaly diminishes with altitude becoming a slightly negative anomaly in the free troposphere. The ozone precursor carbon monoxide shows an 11 % reduction in MAM (March–April–May) near the surface. There is only a small reduction in CO in the free troposphere due to the impact of long-range transport on the CO from emissions in regions outside Europe. This is confirmed by data from the Infrared Atmospheric Sounding Interferometer (IASI) using retrievals performed by SOftware for a Fast Retrieval of IASI Data (SOFRID), which display a clear drop of CO at 800 hPa over Europe in March but otherwise show little change to the abundance of CO in the free troposphere.

Changes of Anthropogenic Precursor Emissions Drive Shifts of Ozone Seasonal Cycle throughout Northern Midlatitude Troposphere

Simulations by six CMIP6 Earth System Models indicate that the seasonal cycle of baseline tropospheric ozone at northern midlatitudes has been shifting since the mid-20th Century. Beginning in ~ 1940 the seasonal cycle increased in amplitude by ~ 10 ppb (measured from seasonal minimum to maximum), and the seasonal maximum shifted to later in the year by about 3 weeks. This shift maximized in the mid-1980s, followed by a reversal – the seasonal cycle decreased in amplitude and the maximum shifted back to earlier in the year. Similar changes are seen in measurements collected from the 1970s to the present. The timing of the seasonal cycle changes is generally concurrent with the rise and fall of anthropogenic emissions that followed industrialization and subsequent implementation of air quality emission controls. We quantitatively compare the temporal changes of the ozone seasonal cycle at sites in both Europe and North America with the temporal changes of ozone precursor emissions across the northern midlatitudes and find a high degree of similarity between these two temporal patterns. We hypothesize that changing precursor emissions are responsible for the shift in the ozone seasonal cycle, and suggest the mechanism by which changing emissions drive the changing seasonal cycle: increasing emissions of NOX allow summertime photochemical production of ozone to become more important than ozone transported from the stratosphere and increasing VOCs lead to progressively greater photochemical ozone production in the summer months, thereby increasing the amplitude of the seasonal ozone cycle. Decreasing emissions of both precursor classes then reverse these changes. The quantitative parameter values that characterize the seasonal shifts provide useful benchmarks for evaluating model simulations, both against observations and between models.

Investigations of Structural and Electrical Properties of ALD Films Formed with the Ozone Precursor

The continuous development of ALD thin films demands ongoing improvements and changes toward fabricating materials with tailored properties that are suitable for different practical applications. Ozone has been recently established as a precursor, with distinct advantages over the alternative oxidizing precursors in the ALDs of advanced dielectric films. This study reports alumina (Al2O3) and hafnia (HfO2) formation using an O3 source and compares the obtained structural and electrical properties. The performed structural examinations of ozone-based materials proved homogenous high-k films with less vacancy levels compared to water-based films. The enhanced structural properties also result in the problematic incorporation of different dopants through the bulk layer. Furthermore, analysis of electrical characteristics of the MIS structures with ALD gate dielectrics demonstrated the improved quality and good insulating properties of ozone-based films. However, further optimization of the ALD technique with ozone is needed as a relatively low relative permittivity characterizes the ultra-thin films.

Climate Change will Increase Ozone Levels and Unravel Air Quality Regulations

Using daily data for the United States over the period 1980-2019, we estimate the impacts of temperature on ambient ozone concentrations, accounting for adaptation to climatic change. We find that even with adaptation, rises in temperature will steeply increase ozone levels by over 9 ppb on days above 25◦ C. By mid-century, we calculate that 189 additional counties 15 will be violating the air quality standards, with 33 million more residents exposed to unhealthy levels of ozone. Climate change will thus likely increase the costs of compliance with existing ambient ozone standards. In light of a recent EPA ruling that would effectively remove cobenefits of ozone precursor reductions from the cost-benefit analysis of those standards, they will be in peril, further threatening public health.

Climate Change will Increase Ozone Levels and unravel Air Quality Regulations

Using daily data for the United States over the period 1980-2019, we estimate the impacts of temperature on ambient ozone concentrations, accounting for adaptation to climatic change. We find that even with adaptation, rises in temperature will steeply increase ozone levels by over 9 ppb on days above 25◦C. By mid-century, we calculate that 189 additional counties will be violating the air quality standards, with 33 million more residents exposed to unhealthy levels of ozone. Climate change will thus likely increase the costs of compliance with existing ambient ozone standards. In light of a recent EPA ruling that would effectively remove co-benefits of ozone precursor reductions from the cost-benefit analysis of those standards, they will be in peril, further threatening public health.

Climate Change Will Unravel Air Quality Regulations

Using daily data for the United States over the period 1980-2019, we estimate the impacts of temperature on ambient ozone concentrations, accounting for adaptation to climatic change. We find that even with adaptation, rises in temperature will steeply increase ozone levels by over 9 ppb on days above 25◦C. By mid-century, we calculate that 189 additional counties will be violating the air quality standards, with 33 million more residents exposed to unhealthy levels of ozone. Climate change will thus put the ambient ozone standards at risk as the costs of compliance with existing standards will likely increase. In light of a recent EPA ruling that would effectively remove co-benefits from ozone precursor reductions from the cost-benefit analysis of those standards, they will be in peril.

The Potential Ozone Impacts of Landfills

Landfill gas produces ozone precursors such as nitrogen oxides and formaldehyde when combusted in flares or stationary engines. Solid waste landfills are also the third largest anthropogenic source of methane in the United States. Methane is both a greenhouse gas and a tropospheric ozone precursor. Despite its low photochemical reactivity, methane may noticeably affect urban ozone if released in large quantities along with other organic compounds in landfill gas. A fine-scale 3D Eulerian chemical transport model was used to demonstrate that, under meteorological and background chemical conditions conducive to high ozone concentrations, typical emissions of ozone precursors from a single hypothetical landfill may result in persistent daytime additions to ozone of over 1 part per billion (ppb) by volume tens of kilometers downwind. Large leaks of landfill gas can enhance this ozone pollution by over a tenth of a ppb, and external sources of non-methane ozone precursors may further exacerbate this impact. In addition, landfill gas combustion may increase near-source exposure to toxic formaldehyde by well over half a ppb. In Southeast Michigan, the combined influence of several landfills upwind of key monitoring sites may contribute significantly to observed exceedances of the U.S. ozone standard.