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.

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.

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.

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.

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.

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.

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

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.

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 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.

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 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.

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.

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.

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 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.

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.

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.

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.

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.

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.

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 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.