A continental-scale plume of carbon monoxide (CO) and other air pollutants from active fires in Siberia is being mapped in near real-time by ACOM scientists, based on data provided by TROPOMI (the TROPOspheric Monitoring Instrument, on board ESA's Sentinel-5P platform). Figures 1 and 2 illustrate the magnitude of CO emissions during this fire season (summer 2019) compared to the same period last year (2018).
About half of atmospheric carbon monoxide (CO) is from direct (CO) emissions that are due to incomplete combustion and are related to both natural (e.g. wildfires) and anthropogenic activities. The remainder of CO in the atmosphere is produced from the chemical oxidation of hydrocarbons, mainly from biogenic sources and methane (CH4). Since most of the hydrocarbons, CO, and CH4 in the atmosphere are oxidized by the hydroxyl radical (OH), the associated chemical lifetimes of these species are strongly coupled with OH.
Wildfires tend to be more intense and hence costly and are predicted to increase in frequency under a warming climate. For example, the recent August 2015 Washington State fires were the largest in the state’s history. Such large fires impact not only the local environment but also affect air quality far downwind through the long-range transport of pollutants. Global to continental scale coverage showing the evolution of CO resulting from fire emission is available from satellite observations.
ACOM Scientists recently participated in a field campaign in a forested area of Northern Michigan. The PROPHET-AMOS campaign – Program for Research on Oxidants; Photochemistry, Emissions and Transport - Atmospheric Measurements of Oxidants in Summer – took place through the month of July 2016 at the PROPHET Lab and Tower near Pellston, MI. The goal of the project was to study the cycling of chemicals between the biosphere and the atmosphere, and to understand the roles of various oxidants above and within the canopy of a northern forest.
A multitude of recent atmospheric observations show that organic aerosols are ubiquitous and often more abundant than other particles such as sulfate, nitrate, soot, and dust. These large amounts of organic particles contribute to the health impacts of air pollution, to regional visibility reductions, to both cooling and warming tendencies of radiative forcing, and to modified cloud properties and precipitation patterns. Uncertainties remain in all aspect of their lifecycle, i.e., their formation, transformations and properties, and especially their removal.
The CESM-CAM-Chem/DART data assimilation system is used to investigate and assess the impact of assimilating CO retrieved profiles from two satellite instruments (IASI and MOPITT) on constraining the forecast and analysis of CO in CAM-Chem. The two instruments provide different and complementary capabilities in constraining CO. While the multispectral retrievals from MOPITT have enhanced sensitivity toward the surface and across the main CO source regions, its coverage is relatively limited.
Secondary organic aerosol (SOA) production in urban and biogenic outflow was investigated using the explicit gas-phase chemical mechanism generator GECKO-A [Lee-Taylor et al., 2015]. Urban outflow simulations show several-fold increases in SOA mass continuing for multiple days, whereas forest outflow simulations showed only modest SOA mass increases, and no long-term growth. The multiday SOA production in urban-origin air stems from multigenerational oxidation products of gas-phase precursors which persist in equilibrium with the particle phase.
During certain times of the year, the atmosphere above Brazil’s Amazon Basin is so clean that it has prompted some scientists to refer to this region as the “Green Ocean.” Because its atmosphere is typically clean, changes in the atmosphere, such as the introduction of particles due to biomass burning or emissions of sulfur dioxide from power generators, can profoundly impact processes such as cloud formation, and thereby impact regional climate and precipitation.
Current analysis of the FTS (Fourier Transform Spectrometer) NCAR / NDACC (Network for the Detection for Atmospheric Composition Change) data show secular increases in several species. Focusing on HCl, the largest reservoir of chlorine in the stratosphere due to reduced emissions through the 1990's the total column amounts were observed to be decreasing starting in 1997-1998 [Rinsland et al, 2003]. This was until about 2007 when that trend appeared to be reversing. Now with the benefit of several years of observations the secular increase is quite evident. Fig 1.
Removal of secondary organic aerosols (SOA) from the atmosphere has been studied far less than its equal, production. In current regional and global chemistry models rainout is the dominant loss of SOA. Here we show the importance of a less direct pathway, in which large scale evaporation of SOA particles occurs as a re-adjustment to gas-particle partitioning when semi-volatile organic gases are lost by dry deposition to the Earth’s surface.
ACD scientists in collaboration with colleagues from seven universities successfully sampled atmospheric composition over the Western Pacific warm pool region during the season characterized by massive convective storms. The CONvective TRansport of Active Species in the Tropics (CONTRAST) experiment successfully concluded its field phase during January-February 2014.
Regional chemistry-climate model simulations of present and future conditions were performed to assess changes in surface ozone in the summertime U.S. [Pfister et al., 2014]. The Nested Regional Climate Model with Chemistry (NRCM-Chem), based on WRF-Chem, was used to simulate, at high spatial resolution, the present and a 2050 future time period under the A2 climate and Representative Concentration Pathway (RCP) 8.5 anthropogenic precursor emission scenarios.
Recent research suggests that in-cloud and in-particle chemistry could contribute substantially to the formation of SOA. Glyoxal is one of the precursors proposed to be important. In Knote et al. (2013) we included the state of knowledge on SOA formation from glyoxal into WRF-chem and conducted simulations over California as well as the continental United States for summer 2010.
Fires in Amazonia principally occur during the dry season lasting roughly from July to October and are concentrated in the 'arc of deforestation' spanning across the southern and eastern basin margins. While much of the biomass burning activity in Amazonia follows directly from deforestation associated with agricultural practices, human-caused fires often escape from deforested areas into neighboring standing forests. These fires typically burn below the forest canopy and cause long-term dama
A regional nuclear conflict between India and Pakistan would not only inflict immediate damage in the subcontinent, including massive loss of life and destruction of built infrastructure; severe long-term environmental damage would also spread globally, lasting decades, researchers have found.
The Montreal Protocol on Substances that Deplete the Ozone Layer and its amendments mandate assessments of the status of atmospheric ozone every four years. A key input to these assessment reports is derived from integrations of models that simulate the past, present, and future chemistry of the ozone layer. Integrations using the whole atmosphere option of the CESM are underway for the upcoming 2014 assessment. This model, known as the Whole Atmosphere Community Climate Model (WACCM), simulates interactive chemistry from the Earth’s surface to above 100 km.
HIRDLS observations have shown a strong increase in gravity wave momentum flux (MF) in the stratosphere as a result of deep convection due to the monsoons. Annualised measurements of GW MF from HIRDLS (Figure 1, top) show a strong positive correlation with rainfall (blue line) and a strong anticorrelation with outgoing longwave radiation (green line), a standard proxy for convective activity. Measurements suggest that the Indian monsoon leads to a 25% increase in the measured momentum flux levels in this region, with half the annual total MF generated during the monsoon season.
Clouds are an important part of the earth's climate due to their absorption, emission, and reflectance of radiation. Understanding their formation and properties is critical to predicting earth's present and future radiative budgets. All of the water droplets within clouds were formed by condensation of water onto initial seed particles called cloud condensation nuclei (CCN), or ice nuclei (IN) in the case of ice clouds.
The composition and magnitude of volcanic gas emissions contain keys to understanding and predicting volcanic events. Additionally, some volcanic gases have a positive radiative forcing and thus impact climate. Volcanic gases are mostly analyzed in situ or using airborne instruments, with all the consequent limitations in safety and sampling, and at elevated costs.
The mean circulation of the tropical lower stratosphere is characterized by upwelling, which transports air masses across the tropopause into the lower stratosphere. This is part of the global overturning Brewer-Dobson circulation. However, this upwelling circulation is weak and cannot be measured directly, but is inferred from diagnostic calculations or observed tracer transport.
Accurate NOx emissions are essential for air pollution quantification and mitigation. Combustion processes in the transportation, industrial, and residential sector and emissions from power plants are the dominant anthropogenic sources of NOx. In addition to contributing to the formation of ground-level ozone and fine particle pollution, high levels of NOx are linked with a number of adverse effects on the respiratory system.
A proposed method for geo-engineering climate involves the injection of sulfur into the tropical stratosphere. The resulting enhanced global stratospheric aerosol burden would reflect and scatter sunlight, reducing the Earth’s surface temperature and ultraviolet (UV) radiation intensity. Chemical reactions on the surface of aerosol particles would enhance heterogeneous reactions and alter the ozone abundance, which would change surface UV radiation.
The NCAR CESM system is facilitating the investigation of the interactions among different components of the earth-atmospheric system. One of the available atmospheric models is WACCM, which was specifically developed to simulate interactions between chemistry and climate across all levels of the atmosphere. WACCM simulations are particularly valuable in exploring the impact of middle atmosphere dynamics and chemistry on the climate system.
The High Resolution Dynamics Limb Sounder (HIRDLS) instrument provides measurements of temperature, trace constituents and aerosols from the middle troposphere to the mesosphere. HIRDLS water vapor will be available for the first time in the soon to be released Version 7. Shown are zonal mean comparisons with MLS v3.3 and profile comparisons with a balloon-borne Cryogenic Frost-point Hygrometer (CFH). The precision is ~10%, and the bias is about 10% in the stratosphere and is typically 10-20% in the UTLS.
In collaboration with researchers from the State University of New York’s College of Environmental Science and Forestry in Syracuse, ACD scientists have measured the fractionation of deuterated methoxy radicals, CH2DO, which are formed in the atmospheric oxidation of methane. Methane, CH4, is the most-abundant hydrocarbon in the atmosphere, as a result of its large source strength and low rate of reaction with OH radicals. Its oxidation provides a global background sink for OH and a source of CO.
ACD scientists Tiffany Duhl and Alex Guenther have developed a model that simulates the release of wind-dispersed pollen from vegetation. In collaboration with colleagues at the California Institute of Technology and Washington State University, they are using the model to address the question of how pollen occurrence may be affected by climate change and interact with anthropogenic pollutants to affect human health in a changing world.
Photochemical smog is a byproduct of the NOx-catalyzed oxidation of volatile organic compounds (VOCs) under solar ultraviolet (UV) radiation. While the chemical regime can be NOx-limited, VOC-limited, or NOx-inhibited, it is always photon limited and therefore sensitive to changes in the UV radiation field. In polluted regions, these radiation changes can be caused by the smog itself, especially ozone (O3), nitrogen dioxide (NO2), and aerosol particles.
Nitrogen oxides, through their interactions with volatile organic compounds (VOCs), NH3, OH, and other gas-phase species, exert important controls on the lifetime and fate of atmospheric VOCs and the formation of secondary aerosol. During the night, the nitrate (NO3) radical is an important oxidant, reacting rapidly with unsaturated VOCs, many of which are biogenic in origin (BVOC), to produce organic nitrates and other oxidized VOCs, some of which lead to the formation of secondary organic aerosol.
The new Version 5 (“V5”) MOPITT (Measurements of Pollution in the Troposphere) product for carbon monoxide (CO) is the first satellite product to exploit simultaneous near-infrared (NIR) and thermal-infrared (TIR) observations to enhance retrieval sensitivity in the lower troposphere. Since most major sources of tropospheric CO are found at or near the Earth's surface, this feature will improve air quality forecasts and studies of CO sources.
Aura’s High Resolution Dynamics Limb Sounder (HIRDLS) reveals the global pattern of the double tropopause using the HIRDLS high vertical resolution profiles. Composition and structure near the tropopause are important for the Earth radiative balance and quantifying transport of ozone and other stratospheric species into the troposphere.
The extratropical upper troposphere and lower stratosphere (Ex‐UTLS) is a transition region between the stratosphere and the troposphere. In this region, dynamics, chemistry, clouds and radiation are strongly coupled, which makes this region important for chemistry-climate interactions. Significant progress has been made in understanding the climate-relevant processes in this region during the last decade, assisted by a suite of new observational studies.
The MOPITT multispectral CO product along with model simulations from WRF-Chem have recently been applied to analyze emissions of both CO and CO2 during the 2008 Beijing Summer Olympics. The results suggest that urban traffic controls instituted during the Olympics significantly reduced emissions of CO and CO2. A manuscript by H. Worden, et al., describing this pioneering work has recently been submitted to Geophysical Research Letters.
A new ozonesonde climatology for the period 1995-2009 was compiled for model evaluation and comparison to other observations [Tilmes et al., 2011]. This climatology allows evaluating the performance of ozone especially in the troposphere and lower stratosphere. Various models still show significant shortcomings to reproduce the structure and seasonality of ozone, one of the most important trace gases in the atmosphere.
The Whole Atmosphere Community Climate Model (WACCM) simulates many features of the stratosphere, including the very active dynamics in Northern Hemisphere winter. During midwinter in some years, there are major breakdowns of the polar winter vortex known as sudden stratospheric warmings. The frequency and development of these events simulated in WACCM are similar to observations.
New particle formation, the spontaneous creation of new nanometer-sized particles in the atmosphere, is often the dominant source of particles in remote regions. A major part of newly formed aerosol consists of organic material that can be attributed to photo-chemically reacted volatile organic compounds emitted by vegetation. Understanding the mechanisms responsible for the growth of these biogenic nanoparticles into sizes where they may scatter radiation efficiently or change cloud properties is vitally important for assessing the impacts of new particle formation on climate.
During the summer of 2010, large areas of central Russia were devastated by extensive wildfires burning through forests and dry peat bogs. In addition to the threat from the actual fires, the smoke and pollutants generated by the fires created an air quality crisis for millions of Russians, including residents of Moscow. Figure 1 below shows imagery from the MODIS satellite instrument for Aug. 8; a vast smoke plume is clearly evident.
The tropopause is a fundamental boundary of the atmosphere, separating the turbulent mixing dominated troposphere from the much more stable and stratified stratosphere. To examine the role of the tropopause and the jet streams in constraining the cloud distributions, ACD scientists performed an analysis of cloud top and tropopause relationships using the Cloud-Aerosol Lidar Infrared Pathfinder Satellite Observations (CALIPSO) cloud data and National Centers for Environmental Prediction (NCEP) Global Forecast System (GFS) tropopause data.
Understanding the spatio-temporal distribution of air pollution is made easier if we are able to differentiate between the different processes driving pollutant variations. This involves understanding how the surface and tropospheric concentrations at a given time and location are governed by direct emissions of pollution, chemical processing and transport into the region from further afield.
The importance of lateral boundary conditions (BC) in regional atmospheric transport models or numerical prediction models has been well established in the meteorological community. Much more recently, attention has also been drawn to the consideration of chemical lateral boundary conditions in regional chemical transport models (CTMs) and in air quality simulations, and the importance of the inflow of pollution on local air quality.
El Nino-Southern Oscillation (ENSO) is the largest source of interannual variability in the tropical troposphere. Some studies have documented the propagation of the ENSO signal to the stratosphere (Calvo Fernandez et al., 2004; Sassi et al., 2004; Garcia-Herrera et al. 2006) through the anomalous propagation and dissipation of ultralong Rossby waves at middle and high latitudes, which modify the stratospheric mean meridional circulation. A recent study using the Whole Atmosphere Community Climate Model (WACCM3.5), has also shown the intensification of the tropical upwelling in the lowermost part of the stratosphere, below 20km, during warm ENSO events and its weakening during the opposite phase (Calvo et al. 2010). This is mainly due to anomalous forcing by orographic gravity waves especially during the strongest warm ENSO episodes; as a result of anomalies in the location and intensity of the subtropical jets and in the meridional gradient of temperature observed during ENSO episodes.
The vertical depths of cirrus in the upper troposphere vary from less to a kilometer to many kilometers. There is interest in knowing these depths in order to understand how cirrus contributes to the heating and cooling rates in the upper troposphere – a positive solar plus infrared heating rate will impart a positive enhancement to the vertical motion field. Measurements of cirrus by the HIRDLS experiment add to our knowledge base, since the HIRDLS experiment is sensitive to the presence of small amounts of cirrus along limb-views in the upper troposphere.
Figure 1: Locations of recent measurement campaigns that involved POP group observations. Right-click to view larger images.
The HIRDLS satellite reveals the structure of the Upper Troposphere / Lower Stratosphere (UTLS) region by measuring ozone.
NASA’s SABER (Sounding of the Atmosphere using Broadband Emission Radiometry) instrument on the TIMED satellite measures temperature and ozone through the middle atmosphere from 20 to above 100 km. The SABER measurements in NH winter (mid-January through mid-March) capture the evolution of ozone and temperature during recent unusual winters (Figure 1). It is now well documented that the altitude of the temperature maximum (stratopause) was elevated for significant periods in 2004, 2006, and 2009.
The global chemical transport model MOZART-4 has been recently released to the scientific community through the ACD MOZART-4 homepage and the NCAR Community Data Portal. The description of MOZART-4 has been submitted to the online journal Geoscientific Model Development [Emmons et al., 2009].
Satellite observations have revealed that cirrus is very prevalent near the tropopause throughout most of the tropics. Cirrus is formed by several processes: a) in-situ rising and freezing of a humid layer, b) blow-off by deep convection, and c) initiation of cirrus formation by the cold temperature perturbations of dynamical waves. The cirrus is of interest since the cirrus restricts the amount of water vapor that is transported from the upper troposphere into the lower stratosphere.
The MOPITT team has made significant advances in demonstrating multispectral retrievals of CO (carbon monoxide) with enhanced sensitivity to near-surface CO. MOPITT, (Measurements Of Pollution In The Troposphere), on EOS-Terra, has been measuring CO since March 2000, and is the only satellite instrument with both thermal infrared (TIR) and near infrared (NIR) CO channels. The standard MOPITT V4 product uses TIR-only radiances to produce CO distributions for day/night, ocean/land observations.
The production of new particles following atmospheric nucleation is a frequently-observed, worldwide phenomenon. Nanoparticles produced by atmospheric nucleation can subsequently grow to become cloud condensation nuclei (CCN) within one or two days and hence affect cloud formation, precipitation, and atmospheric radiation budgets. Bridging between molecules and nanoparticles, neutral molecular clusters are believed to play an important role in boundary layer nucleation process.
The mechanisms by which secondary organic aerosols (SOA) form in the atmosphere are a topic of much current research. Parameterizations used in air quality and climate have difficulty reproducing observed quantities of ambient aerosol, at least in part because of their inability to account for the diversity of chemical species involved in SOA formation.
Increasing anthropogenic pollution and wildfires are the main producers of CO (carbon monoxide) pollution in the Northern Hemisphere. During the NASA ARCTAS field campaign , the ACRESP group used models and satellite data to study the polluted air masses that are transported into the Arctic troposphere, influencing the ecosystem in high northern latitudes and the global radiation and climate.
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