A13F-01
Importing Ozone Precursors to the North American Free Troposphere: Spring 2008 Peroxyacetyl Nitrate (PAN) and NOx Observations from Mount Bachelor
In response to the continuing increase in Asian NOx (NO + NO2) emissions, several international field campaigns have focused on understanding the formation of ozone (O3) in pollution plumes as they cross the Pacific. Limited case studies suggest that NOx released from the thermal decomposition of PAN may represent a significant source of imported O3. Despite this hypothesis, the PAN measurement record along the west coast of North America remains sparse, both spatially and temporally. A suite of gas phase and aerosol measurements were made during spring 2008 at Mount Bachelor (2763 masl), located in central Oregon. Here we focus on observations of PAN, made by gas chromatography with electron capture detector, for the period of 3 April to 18 June 2008. During this period PAN mixing ratios ranged from below detection limit (~15 pptv) to 526 pptv, with a campaign mean of 119 ± 73 pptv. During two periods of elevated PAN, backward trajectory calculations indicate that the air spent time in the Asian continental boundary layer prior to reaching Mount Bachelor. These events, observed on 17-19 April and 12-13 May, were both associated with elevated levels of CO, O3, NOx and aerosol scattering. On 18 April PAN, NO2, O3 and CO reached mixing ratios of 526 pptv, 532 pptv, 71 ppbv, and 195 ppbv respectively. These were the highest NO2 and PAN mixing ratios detected during the campaign. On 12 May the peak mixing ratios for these compounds were lower: 305 pptv, 219 pptv, 68 ppbv, and 168 ppbv, respectively. The peak PAN mixing ratio occurred at approximately 8:00 AM local time during both events, followed by a peak in NO2 later near local sunset. In both cases the air masses arrived at Mount Bachelor under subsiding conditions, and the peak PAN mixing ratios were associated with low water vapor mixing ratios (~1.5 g/kg). The campaign hourly mean NO2 mixing ratio near sunset was 144 ± 74 pptv, thus both events indicate levels of NO2 well above background conditions. In an effort to understand how mixing and subsidence during trans-Pacific transport may have impacted the PAN to NOx ratio and in-plume O3 production for each of these events, we trace the evolution of the plumes using a 3D global chemical transport model (GEOS-Chem). We also explore the local meteorological conditions supporting each pollution event to understand the degree to which differences in upslope/downslope flow on the mountain may have impacted the observations.
A13F-02
Assessing scales of variability for atmospheric composition field data relevant to future Decadal Survey satellite observations
Establishing appropriate specifications for satellite observations of atmospheric composition is a difficult and inexact task since neither models nor observations can provide both the resolution and spatial coverage required. Nevertheless, instrument specifications need to be supported by careful and detailed modeling analyses (e.g., OSSEs) and examination of available in situ observations. Despite shortcomings in temporal and spatial coverage, field observations are unique in capturing true atmospheric variability on scales down to and below those of satellite observations. Here we assess the spatial variability of field observations useful for establishing measurement requirements for future Decadal Survey observations (e.g., GEO-CAPE, GACM, and ASCENDS).
A13F-03
TES Observations of Global Tropospheric Ozone and CO: Characteristics of Their Seasonal and Vertical Distributions
With over four years observations of tropospheric Ozone and Carbon Monoxide, the Tropospheric Emission Spectrometer (TES) on board NASA's Aura satellite provides a wealth of information on their temporal and spatial distribution and their relationships for atmospheric chemistry studies. TES Ozone and CO global monthly averages at three levels of the troposphere and the time trends of their vertical distributions for over thirty regions of the globe have been posted on the TES public website, http://tes.jpl.nasa.gov. The selections of the regions for time-pressure images in the tropics and mid latitudes are mainly based on known pollution sources and downwind regions. These time series qualitatively demonstrate seasonally varying horizontal and vertical distribution characteristics of O3 and CO mostly existing in global chemistry-transport model simulations. The seasonal distributions of global ozone and CO in the tropopsphere are determined by their source and sink mechanisms, the photochemistry, and transport. In the tropics, CO sources are dominated by biomass burning over the continents during the dry season and the ozone values are observed to be positively correlated in the lower troposphere with enhanced CO near CO source regions and in the mid-troposphere downwind of the CO source. In the Northern mid-high latitudes, the CO values are seen increasing from winter to their peak in spring. The pollution sources (e.g, E. China) and the transport patterns are recognizable in CO distributions. In the mid-troposphere, ozone reaches its highest level in spring through summer. However, in the lower troposphere, summer time ozone values are highest over mid-latitude continents but lowest over the oceans.
A13F-04
Exploring CO Pollution Episodes Observed at Rishiri Island by Chemical Weather Simulations and AIRS Satellite Measurements: Long-range Transport of Burning Plumes and Implications for Emissions Inventory
The summer of 2003 was active forest fire season in Siberia. Several elevated events of carbon monoxide (CO) were observed at Rishiri Island in northern Japan during an intensive field campaign in September, 2003. A simulation with a global chemistry-transport model is able to reproduce the general features of the baseline levels and variability in the observed CO, and a source attribution for CO in the model suggests that the contribution from North Asia dominated, accounting for approximately 50% on average, with contributions of 7% from North America and 8% from Europe, and 30% from oxidation of hydrocarbons. With consideration of recent emission estimates for East Asian fossil fuel and Siberian biomass burning sources, the model captures the timing and magnitude of the CO enhancements in two pollution episodes well (September 17 and 24). However, it significantly underestimates the amplitude during another episode (September 11-13), requiring additional CO emissions for this event. Daily satellite images from AIRS reveal CO plumes transported from western Siberia toward northern Japan. These results suggest that CO emissions from biomass burning in western Siberia in 2003 are underestimated in the inventory, and further highlight large uncertainties in estimating trace gas emissions from boreal fires.
A13F-05
Joint Application of Concentrations and Isotopic Signatures to Investigate the Global Atmospheric Carbon Monoxide Budget: Inverse Modeling Approach
Carbon monoxide is not only an important component for determining the atmospheric oxidizing capacity but also a key trace gas in the atmospheric chemistry of the Earth's background environment. The global CO cycle and its change are closely related to both the change of CO mixing ratio and the change of source strength. Previously, to estimate the global CO budget, most top-down estimation techniques have been applied the concentrations of CO solely. Since CO from certain sources has a unique isotopic signature, its isotopes provide additional information to constrain its sources. Thus, coupling the concentration and isotope fraction information enables to tightly constrain CO flux by its sources and allows better estimations on the global CO budget. MOZART4 (Model for Ozone And Related chemical Tracers), a 3-D global chemical transport model developed at NCAR, MPI for meteorology and NOAA/GFDL and is used to simulate the global CO concentration and its isotopic signature. Also, a tracer version of MOZART4 which tagged for C16O and C18O from each region and each source was developed to see their contributions to the atmosphere efficiently. Based on the nine-year-simulation results we analyze the influences of each source of CO to the isotopic signature and the concentration. Especially, the evaluations are focused on the oxygen isotope of CO (δ18O), which has not been extensively studied yet. To validate the model performance, CO concentrations and isotopic signatures measured from MPI, NIWA and our lab are compared to the modeled results. The MOZART4 reproduced observational data fairly well; especially in mid to high latitude northern hemisphere. Bayesian inversion techniques have been used to estimate the global CO budget with combining observed and modeled CO concentration. However, previous studies show significant differences in their estimations on CO source strengths. Because, in addition to the CO mixing ratio, isotopic signatures are independent tracers that contain the source information, jointly applying the isotope and the concentration information is expected to provide more precise optimization results in CO budget estimation. Our accumulated long-term CO isotope measurement data contribute to having more confidence of the inversions as well. Besides the benefit of adding isotope data on the inverse modeling, a trait of each isotope of CO (oxygen and carbon isotope) contains another advantageous use in the top-down estimation of the CO budget. δ18O and δ13C has a distinctive isotopic signature on a specific source; combustion sources such as a fossil fuel use show clearly different values from other natural sources in the δ18O signatures and the methane source can be easily separated by using δ13C information. Therefore, inversions of the two major sources of CO respond with different sensitivity for the different isotopes. To maximize the strengths of using isotope data in the inverse modeling analysis, various coupling schemes combining [CO], δ18O and δ13C have been investigated to enhance the credibility of the CO budget optimization.
A13F-06
HOx Radical Chemistry in the Pearl River Delta in China 2006
The PRIDE-PRD 2006 campaign took place close to the mega-city Guangzhou in the Pearl River Delta (PRD) in South China in July 2006. It offered, for the first time, an opportunity to investigate the tropospheric photochemistry in a densely populated region in China by direct radical measurements. Concentrations of OH and HO2 were simultaneously measured by laser-induced fluorescence (LIF) with high time resolution, together with the OH reactivity (reciprocal OH lifetime), which was recorded by a newly developed UV-pump LIF-probe technique. In addition, a comprehensive set of other important trace gases (e.g., O3, H2O, CO, CH4, NMHCs, isoprene, NO, NO2, HONO etc.) and photolysis frequencies were measured. The experimental data indicate that the photochemistry was very active under the polluted conditions encountered in PRD, with high OH levels reaching 2 x 107 cm-3 during daytime. In this presentation, the chemical OH budget will be analyzed with respect to its measured chemical sources and sinks, and HOx radical concentrations will be compared with box model calculations that are constrained by measurements. Consequences for the photochemical formation of ozone will be discussed.
A13F-07
A European Network for Atmospheric Hydrogen observations and studies: EUROHYDROS
and the EuroHydros team In a future energy supply chain, molecular hydrogen is expected to play an increasingly important role as a carrier of energy for mobile applications, in particular in the automotive sector. Such an increased use of molecular hydrogen is prone to lead to additional emissions into the atmosphere, due to leakages in the supply chain. While molecular hydrogen does not influence the radiation budget of the atmosphere directly, it affects its oxidation capacity, through reaction with the OH radical. This in turn leads to an increased atmospheric lifetime of many atmospheric constituents (e.g. Methane), making H2 an indirect greenhouse gas. An increase of molecular hydrogen in the atmosphere also leads to increasing H2O in the stratosphere, influencing the radiation budget of the atmosphere and ozone chemistry. In the light of these uncertainties, a thorough understanding of hydrogen in the atmosphere is necessary, and, most notably, a good understanding of the present day global distribution and budget of atmospheric hydrogen. The EU funded project Eurohydros aims at improving the understanding of the budget of molecular hydrogen in the atmosphere through a combination of atmospheric monitoring, source-sink studies and modelling work. In this presentation we focus on the observational network, showing first results from different European and Global sites, from the calibration of the data sets and a first intercomparison experiment.
A13F-08
Regulated Large-Scale Shutdown of Amazonian Isoprene Emissions Inferred From GOME and SCIAMACHY Observations of HCHO Columns
We perform Empirical Orthogonal Function analysis on 12 years of global GOME and SCIAMACHY formaldehyde (HCHO) column observations, to determine the most significant spatial and temporal HCHO variations. In most regions, we find that HCHO variability is predominantly driven by seasonal variations of biogenic emissions and biomass burning. However, unusually low HCHO columns are consistently observed over western Amazonia, during the transition from the wet-to-dry seasons. We present top-down isoprene emissions over western Amazonia during 1997-2001 inferred GOME HCHO columns, the GEOS-Chem chemistry transport model and the MEGAN (Model of Emissions of Gases and Aerosols from Nature) bottom- up isoprene inventory. The seasonal variation of GOME isoprene emissions is broadly consistent with MEGAN, with the smallest emissions during the wet-to-dry transitional period. The largest isoprene emissions are during the dry season, when the observed variability is consistent with prior knowledge of temperature dependence. We use MODIS Leaf Area Index and Enhanced Vegetation Index data, to show variations in vegetation are remarkably consistent (correlations of 0.69 and 0.67, respectively) with the observed decrease in HCHO during the wet-to-dry period. Based on this evidence, we suggest isoprene emitters experience widespread leaf flushing prior to the dry season, resulting in a large-scale annual shutdown of Amazonian isoprene emissions.