The diurnal cycle of ozone affects metrics that quantify how ozone impacts human health and vegetation. We use a high resolution global atmospheric chemistry model simulation to investigate how the magnitude of the daily cycle in ozone is changing in different regions of the world in response to changes in NOx emissions. The model simulation shows good agreement with the NO2 trends seen by the OMI satellite instrument and with the changes in the daily ozone cycle observed at rural sites in the eastern United States. This gives us more confidence to apply the model to other regions where sufficient surface data is not available. Our simulation predicts that the magnitude of the daily variability in surface ozone increased from the 1980s to present in regions such as China where NOx emissions increased, while the magnitude decreased where emissions decreased. Consequently, both positive and negative trends in peak surface ozone concentrations are stronger than the trends in ozone averaged over the whole day.

The stratospheric mean age of air is the average time that an air parcel spends when it transports from troposphere to stratosphere. The mean age has been robustly shown to decrease in climate simulations of the recent past, indicating an acceleration of the stratospheric transport circulation. The decrease in mean age is caused by two major anthropogenic forcings: greenhouse gas (GHG) increase and stratospheric ozone depletion. However, the relative importance of these two drivers remains uncertain. This study separates the relative impacts of greenhouse gas increase and stratospheric ozone depletion on stratospheric mean age of air in 1960-2010 using the Goddard Earth Observing System Chemistry-Climate Model (GEOSCCM). The simulations show that stratospheric ozone depletion contributes nearly 50% to the simulated decrease of mean age in this period. This result suggests that the projected stratospheric ozone recovery in the 21st century will significantly slow down the acceleration of stratospheric transport circulation.

Reactive halogen gases containing chlorine (Cl) or bromine (Br) can destroy stratospheric ozone via catalytic cycles. The main sources of atmospheric reactive halogen are the long-lived synthetic chlorofluorocarbons (CFCs), hydrochlorofluorocarbons (HCFCs), carbon tetrachloride (CCl4), methyl chloroform (CH3CCl3), and bromine-containing halons, all of which persist in the atmosphere for years. These ozone-depleting substances are now controlled under the Montreal Protocol and its amendments. Natural methyl bromide (CH3Br) and methyl chloride (CH3Cl) emissions are also important long-lived sources of atmospheric reactive halogen. Rising concentrations of very-short-lived substances (VSLSs) with atmospheric lifetimes of less than half a year may also contribute to future stratospheric ozone depletion. A greater concern for ozone layer recovery is incomplete compliance with the Montreal Protocol, which will impact stratospheric ozone for many decades, as well as rising natural emissions as a result of climate change.

Stratospheric aerosols (SAs), tiny droplets and particles suspended high in the atmosphere, primarily cool Earth's surface by reflecting incoming sunlight, potentially offsetting some of the warming caused by increased greenhouse gases. Changes in manmade emissions from the surface and recent volcanic activity may be changing the amount and composition of these particles. New aircraft in-situ and satellite instruments are making measurements of these particles but the sizes, composition, evolution, and sources of these particles are not well known. We compare new airborne in-situ measurements with satellite-based measurements and model simulations of sulpher dioxide gas (SO2), thought to be the dominating source of SAs. We show that the tropical tropopause background SO2 is about 5 times smaller than reported by the average satellite observations. This shifts the view of SO2 as a dominant source of SAs to a near-negligible one, possibly revealing a significant gap in the SA budget.

Deep convection impacts the tropospheric ozone distribution by vertically redistributing ozone and its precursors. Surface air typically has lower ozone concentrations than upper tropospheric air; so convective lifting brings low ozone concentrations to the upper troposphere. On the other hand, over polluted regions it can also bring up pollutants that lead to ozone formation. Clouds also impact ozone chemistry and alter the amount of solar radiation available for ozone production. In this work we test how well global chemistry climate models simulate the impact of clouds and convection on ozone.

Since the beginning of the 1980s, global stratospheric temperatures have decreased at all altitudes. Using the NASA GEOS-5 Chemistry Climate Model, we isolate the role played by 1) greenhouse gases, 2) changing ozone depleting substances, 3) volcanic eruptions, and 4) the solar cycle in producing the long and short-lived features observed in the time series of stratospheric temperature anomalies. Greenhouse gases, while warming the troposphere, cool the stratosphere, and their effect on stratospheric temperature increases with their increasing concentrations. Increases in ozone depleting substances also cool the stratosphere, due to the subsequent decrease in ozone. Sporadic volcanic events and the solar cycle have a distinct signature in the time series of stratospheric temperature anomalies, but do not play a significant role in the long-term trends from 1979 to 2015.

Concentrations of the pollutant carbon monoxide (CO) vary over time due to trends in anthropogenic emissions as well as year-to-year variability in biomass burning. Worden et al. [2013] found significant negative trends in CO observations from MOPITT over the eastern United States, Europe, and eastern China. In this study, we use a suite of global model simulations to interpret the observed trends. We find that simulations using time-dependent emissions reproduce the observed trends over the eastern United States and Europe, but produce a positive trend over eastern China, in contrast with the observed trend. This discrepancy likely indicates that the assumed emission trend over China is too positive, though large variability in the simulated ozone column, which impacts the chemical loss of CO via reaction with OH, also contributes to the differences between model and observations.

Carbon monoxide (CO) plays an important role in tropospheric chemistry. It is the primary sink of the hydroxyl radical (OH), an important atmospheric oxidant, and thus impacts how quickly atmospheric constituents such as methane (CH4) are oxidized. Chemistry climate models (CCMs) often have a low bias in CO in the high northern latitudes. This underestimate of CO could lead to an overestimate of OH, or conversely it is possible that other factors drive a bias in simulated OH, which in turn causes a bias in CO. Determining the cause of CO bias is important for improving model simulations of OH and the lifetime of CH4, a potent greenhouse gas. We examine possible causes of the low bias in northern latitude CO in the GEOS-5 Chemistry Climate Model (GEOSCCM) using a variety of sensitivity simulations. We find that no single factor leads to a large enough decrease in OH to explain the CO bias but all of the adjustments together result in a simulated CH4 lifetime increase that agrees well with observation based estimates.

The Arctic is warming faster than any other region on Earth. One factor accelerating the warming is black carbon (i.e. soot), which reduces the reflectivity of ice and snow. In this study we use a climate model to show that more than 60% of boundary layer air in the Arctic is of midlatitude origin. There are strong seasonal variations in the midlatitude boundary layer regions that supply air to the Arctic - the oceans dominate in winter and the continents in summer. Furthermore, Asia supplies more than 40% of all midlatitude boundary layer air to the Arctic during summer. This is especially concerning since black carbon emissions over Asia have been increasing over recent decades, with little sign of decreasing. As the climate warms circulation patterns over midlatitudes will change. Our results suggest that these changes -- specifically over the East Pacific and Asia -- may contribute to changes in Arctic pollution, irrespective of whether or not pollutant emissions change. Image Credit Energy Information Admin.,US Dept of Energy.

Pollution that is emitted at the Earth's surface and enters the stratosphere can impact stratospheric ozone, water vapor and aerosols, which control key aspects of climate. While most transport to the stratosphere happens over the tropics, recent studies have shown that the Asian monsoon circulation also efficiently transports water vapor and pollution to the extratropical lower stratosphere.In this study we use a climate model to look at the underlying long-term transport that links the Earth's surface to the stratosphere. We show that nearly 20% of air in the tropical lower stratosphere originates in the Asian boundary layer, compared to negligible amounts from North America and Europe. This implies that Asian emissions are much more efficient at reaching the stratosphere than emissions from other populated regions.

Nitrous oxide (N2O) is an important gas that has both natural and humankind sources. N2O impacts the chemical composition of the Earth's atmosphere, including the ozone layer, and also traps infrared radiation that leads to global warming. The destruction in the atmosphere of nitrous oxide occurs either by chemical reaction or by ultraviolet (UV) light from the sun. The rate at which N2O is destroyed can be estimated by laboratory measurements. This rate of destruction can then be used with computer models of the atmosphere and satellite measurements of the N2O concentration to determine how long a molecule of N2O resides in the atmosphere prior to its destruction. This residence time is referred to as the lifetime, and is important in determining the length of time over which a molecule of N2O will have a significant impact on the ozone layer and on global warming. This study provides a detailed analysis of the determination of the N2O lifetime using satellite data together with laboratory measurements of the rate of N2O destruction and several computer models of the global atmosphere.

Geoengineering is the deliberate modification of the Earth's system in order to counteract global warming due to increasing greenhouse gases. One proposed geoengineering method involves the injection of sulfate aerosol in the stratosphere, and aims to reproduce the cooling that has been observed after major volcanic eruptions.The Geoengineering Model Intercomparison Project (GeoMIP) is an international collaboration with the goal of understanding the effects of geoengineering solar radiation management through climate simulations performed with different global climate models. Researchers at NASA Goddard Space Flight Center used the GEOSCCM model to predict the effects of increased sulfate aerosol on stratospheric ozone and and Quasi-biennial Oscillation.

Chemistry-climate models are crucially important to projecting the future evolution of ozone and to understand the factors that drive this change. A new study by scientists at NASA's Goddard Space Flight Center (GSFC) documented and demonstrated improvements to the Goddard Earth Observing System Chemistry-Climate Model (GEOSCCM) specifically focusing on total column ozone. They found that by including more processes known from observations model biases could be significantly reduced. These processes include: the Quasi-Biennial Oscillation of tropical stratospheric winds, variability of observed stratospheric sulfate aerosol, and improvements in the day/night transition in the chemical mechanism among others.

Observations suggest that anomalously high sea surface temperatures (SSTs) in the North Pacific may have led to the sustained period of low temperatures and record-breaking ozone depletion that took place in the Arctic stratosphere in spring 2011. NASA Goddard scientists explore why it is not possible to attribute the precise causes of the stratospheric conditions to just SSTs.

The Sun's radiation output varies over an 11-year cycle. This study looks at how the atmosphere responds to the 11-year solar cycle with two state-of-the-art chemistry-climate models (CCMs): the 3-D GEOSCCM and the GSFC 2-D coupled model, and explains why GCMs without coupled chemistry underestimate the temperature response to the solar cycle.

Featured in NASA's July 2012 Science Highlight.

El Nino Southern Oscillation (ENSO) is the episodic warming or cooling of sea surface temperatures in the eastern and central equatorial Pacific and the dominant mode of interannual tropical variability. It influences the thermal, dynamical, and chemical composition of the troposphere. The response of tropospheric to lower stratospheric ozone to ENSO is derived using measurements from the Microwave Limb Sounder (MLS) and Tropospheric Emission Spectrometer (TES) onboard NASA's Aura satellite.

Featured in NASA's June 2012 Science Highlight.

Volcanic eruptions inject heavy ash particles and gaseous sulfur dioxide into the atmosphere, which is transformed into sulfate aerosol particles through chemical reactions. A major volcano in the Philippines, Mt. Pinatubo, erupted, injecting about 30 Tg (33,069,339 tons) of sulfate into the atmosphere, which diffused over the whole globe within three weeks. Recent studies by scientists at the NASA Goddard Space Flight Center investigate the stratospheric effects of the Mt. Pinatubo eruption.

Featured in NASA's April 2012 Science Highlight.

March temperature in the Arctic stratosphere is highly correlated with tropospheric wave forcing in February (Newman et al., 2001). Meteorological reanalyses show that wave forcing in 2011 was much weaker than usual, consistent with the unusually cold conditions. Similarly weak wave forcing and March temperatures were observed in 1997.

Featured in NASA's August 2011 Science Highlight.

Ozone in the Arctic troposphere is important as a surface pollutant affecting air quality and a greenhouse gas that contributes to Arctic warming. Currently there lacks a clear understanding of how each source, e.g. anthropogenic and biomass burning emissions and stratospheric intrusion, contribute to the ozone abundance in the Arctic troposphere. Scientists at NASA Goddard analyze the aircraft observations obtained during the NASA ARCTAS aircraft mission to examine ozone and reactive nitrogen.

Featured in NASA's May 2011 Science Highlight.

El Nino Southern Oscillation (ENSO) is the dominant mode of tropical variability on interannual timescales. Its influence extends beyond the thermal and dynamical and into the chemical composition of the troposphere. One key atmospheric gas that past studies have shown to be influenced by ENSO is ozone. A new study by scientists at NASA Goddard Space Flight Center (GSFC) and Johns Hopkins University uses a comprehensive chemistry-climate model to show the impact that ENSO has on tropical tropospheric ozone.

Featured in NASA's April 2011 Science Highlight.

There are many pathways for an air parcel to travel from the troposphere to the stratosphere, each of which takes different time. The distribution of all the possible transient times, i.e. the stratospheric age spectrum, contains important information on transport characteristics. The problem is that computing seasonally varying age spectra is normally very expensive computationally. However, NASA scientists at Goddard introduce a method to significantly reduce the computational cost for calculating seasonally dependent age spectra, which allows interesting findings.

The Antarctic ozone hole impacts both tropospheric and stratospheric climate, particularly in the summer season. NASA scientists investigate climate change in 1960-2060 using the GEOSCCM chemistry-climate model. The scientific questions addressed are: What is role of the ozone hole in climate change? And: Are circulation changes in the troposphere and stratosphere related to each other?

Featured in NASA's March 2011 Science Highlight.

NASA Goddard scientists investigate two important aspects of tropical expansion using simulations of the 21st century from the Goddard Earth Observing System Coupled Chemistry Climate Model (GEOSCCM). The first aspect is the width of the stratospheric circulation (the Brewer-Dobson circulation) under global warming: it is important to understand whether tropical expansion extends into the stratosphere. The second is the width of the ascending branch of the Hadley cell: studying changes in the Hadley cells upwelling will help to understand what causes the expansion of the Hadley cell's sink branch.

Atmospheric aerosols are small, airborne particles that reside in the atmosphere for time-periods of up to one week. They are from diverse sources such as from the tail pipe of your car to dust and sea spray whipped up by the wind. Their chemical properties are similarly diverse. Some aerosols grow in humid air or mix with particles of other types, and aerosols are the nuclei of the droplets that make up clouds. Just as aerosols are complex, their interactions with the climate are also complex.

Colleagues at NASA's Goddard Space Flight Center and Johns Hopkins University used the GEOSCCM model to explain what factors could potentially be driving changes in ozone in the upper levels of our atmosphere over the 21st century.

Scientists at NASA's Goddard Space Flight Center use the GEOSCCM model to study what might have happened to stratospheric ozone and UV radiation at the Earth's surface if CFCs were still in widespread use. The "world avoided" scenario is a representation of the state of the atmosphere if CFC's had not been regulated by the Montreal Protocol and subsequent amendments.

See the NASA Feature Article on this study.

Colleagues at NASA's Goddard Space Flight Center and Johns Hopkins University use the GEOSCCM model to study projected changes in atmospheric circulation in the late 20th and 21st centuries. Changes in this circulation could potentially act to significantly affect the distribution of ozone as well as substances like chlorine and bromine-containing compounds that destroy ozone, which can impact the timing of the recovery of the ozone layer.

A recent paper by scientists at Johns Hopkins University and NASA's Goddard Space Flight Center used the GEOSCCM chemistry climate model to examine stratospheric water vapor trends and the factors that influence these trends. This work deconstructs the components that determine stratospheric water vapor concentrations so that the dominant impacts, which can change over space and time, can be understood.

The temperature of the stratosphere has decreased over the past several decades. Two causes contribute to that decrease: well-mixed greenhouse gases (GHGs) and ozone-depleting substances (ODSs). In this study scientists use the GEOSCCM model to address attribution of temperature decreases to these two causes and the implications of that attribution for the future evolution of stratospheric temperature.

In this study, scientists use simulations from the GEOSCCM model to try to answer an outstanding scientific question: how does climate change affect ozone recovery? Both greenhouse gases and CFC's alter ozone levels well into the future, and model projections suggest that ozone levels in the post-CFC era will not match those before the advent of CFC's.

See the NASA Feature Article on this study.

The presence of the Antarctic polar vortex is a key ingredient in the formation of the ozone hole, because the air inside the vortex is cold and isolated from lower latitudes, creating ideal conditions for large-scale chemical ozone depletion. Many atmospheric models are not able to reproduce observed winds that bound the vortex in the middle atmosphere. In this study, scientists use the GEOSCCM model to investigate the interactions responsible for vortex formation and the factors that lead to a weaker-than-observed vortex in the model.

Scientists at NASA's Goddard Space Flight Center use an ensemble of GEOSCCM simulations of the 21st century to investigate trends in Antarctic temperature and APSC, a temperature proxy for the area of polar stratospheric clouds. A selection of greenhouse gas, ozone-depleting substance, and sea surface temperature scenarios is used to test the trend sensitivity to these parameters.

In this study, scientists use observations and model output from a series of GOES CCM model experiments to investigate changes in Antarctic stratospheric temperatures resulting from El Nino episodes. In particular, the response to a less common El Nino pattern, the "warm pool" El Nino, is investigated.