A21B-0126
Assimilated Inversion of NOx Emissions Over East Asia Using OMI NO2 Column Measurements
Assimilated inversion on a daily basis using OMI retrieved tropospheric NO2 columns is applied in a regional chemical transport model (REAM) to constrain surface NOx emissions over East Asia. In contrast to the widely used monthly-mean inversion that is a priori dependent, the assimilated inversion is found to be insensitive to the a priori. The assimilated a posteriori emissions from fossil fuel combustion over East Asia are 9.9 Tg N/yr comparable to 10.9 Tg N/yr of the a priori emissions. The estimated soil emissions (1.1 Tg N/yr) account for ~10% of the a posteriori surface emissions in August. Significant changes in the spatial distribution of fossil fuel NOx emissions are found in the assimilated inversions from the a priori or monthly-mean inversions. This improvement is evident in the correlation between observed and simulated tropospheric NO2 columns. The a priori bottom-up inventories are found with a tendency to overestimate the emissions over the economically developed areas and underestimate over the underdeveloped areas in East China.
A21B-0127
Lightning and anthropogenic NOx sources over the U.S. and the western North Atlantic Ocean: Impact on radiative forcing and OLR from space-borne observations
We use the Regional chEmical trAnsport Model (REAM) to investigate the impacts of lightning NOx production and anthropogenic NOx emissions on radiative forcing and outgoing longwave radiation (OLR) over the United States and the western North Atlantic Ocean from June to August 2005. Tropospheric column O3 estimates based on data from the OMI and MLS instruments and vertical O3 profiles from the TES instruments onboard the Aura satellite and the OLR data from NOAA polar orbiting satellites are also used in the study. The REAM-simulated OLR fields on the basis of MM5-derived meteorology capture the spatial distribution of the remotely sensed OLR fields reasonably (R~0.88) with relatively small mean biases (<6%). In the convective outflow regions over North America and the western North Atlantic Ocean, the contribution of lightning NOx production on the summertime tropospheric O3 is smaller than that of anthropogenic sources. However, results in this study reveal that the contribution of lightning-generated NOx on radiative forcing and OLR variations via enhancements in tropospheric O3 is significantly larger than the corresponding effects of anthropogenic NOx emissions. The model results also show similar increases in radiative forcing and OLR over the convective outflow regions originating from the lower latitude regions over North America after the onset of North American monsoon. We will also discuss the heating rate changes associated with the lightning NOx source. The relative radiative impact of NOx produced by lightning over North America is becoming larger as fossil-fuel combustion NOx emissions decrease in recent years.
A21B-0128
North American Pollutant Export Due to Anthropogenic Emissions and Lightning
Power plant NOx emission reductions and their impact on air quality as well as the impact of different meteorological conditions is evaluated by using both a global and regional model. The anthropogenic contribution to North American (NA) pollutant export is evaluated for the summers of 2002 and 2004 by University of Maryland Chemistry and Transport Model (UMD-CTM) driven by GEOS-4 CERES reanalysis data. In the first part, we compare the magnitudes of the NA pollutant export and radiative forcing due to ozone production by NA anthropogenic emissions between the 2002 and 2004 summer seasons. Near surface air was cleaner during the summer of 2004 due to relatively cool temperatures, frequent synoptic disturbances, and reduced emissions. In spite of reduced NOx emissions and abnormally low surface temperatures in summer 2004, we show that the monthly averages of net IR radiative fluxes are greater or similar in magnitude in 2004 than in 2002. We hypothesize that this is because of stronger convective transport of polluted airmasses in the upper troposphere where ozone plays an important climate role. We test a new lightning scheme which was tuned to total flashrates determined by combining National Lightning Detection Network (NLDN) flashrates with climatological IC/CG ratios. We also investigate if 500 moles/flash is an appropriate average LNOx production per flash in midlatitudes. In the second part, we simulate a couple of high ozone episodes using WRF-CHEM at a 48-km horizontal resolution (4x finer than that used in UMD-CTM) and a nested 12km domain covering the Eastern half of the US with trace gas lateral boundary and initial conditions from the UMD-CTM. WRF-CHEM model output is compared with high resolution satellite- (SCIAMACHY NO2, MOPITT CO), aircraft- (INTEX-A) and ground- based measurements (AQS). Lastly, we run the simulation with different lateral boundary conditions from Global Modeling Initiative (GMI) model.
A21B-0129
Evaluating Texas NOx emissions using satellite-based observations and model simulations
Anthropogenic NOx is produced primarily from fossil fuel combustion by motor vehicles, power generation, and industrial processes. Satellite-based measurements have been used to assess NOx emission trends on regional to global spatial scales and daily to annual temporal scales. The small horizontal footprints of current satellite-borne instruments, including SCIAMACHY and OMI, can be used to detect NO2 resulting from NOx emitted by isolated point sources and metropolitan areas in the western US. In this study we examine NOx emissions in the state of Texas by comparing NO2 vertical columns retrieved from these satellite instruments to those predicted by a regional chemical-transport model. Comparisons of satellite-derived and model- calculated NO2 columns over US power plants, where in-stack emission monitoring is carried out, enables a critical evaluation of the key parameters leading to uncertainties in the satellite and model data products. By using the satellite retrieval algorithms and model configurations that produce the best agreement in NO2 columns over power plants in northeastern Texas and elsewhere in the western US, satellite-model comparisons of NO2 columns over Texas cities in turn allow urban NOx emission inventories to be assessed. This work focuses on two large Texas metropolitan areas: Dallas/Fort Worth, where NOx is emitted predominantly by mobile and area-wide sources; and Houston, which, like Dallas, has typical urban sources, but also contains large industrial point sources emitting significant amounts of NOx. Year-to-year and day-of- week changes in the satellite data are used to infer NOx emission trends from point and mobile sources and to evaluate the effectiveness of NOx controls on some of these sources.
A21B-0130
Comparison of NOx Emissions and NO2 Concentrations From a Regional Scale Air Quality Model (CMAQ-DDM/3D) With Satellite NO2 Retrievals (SCIAMACHY) Over the Continental U.S.
Estimated NOx emissions and CMAQ simulated NO2 concentrations obtained from these emissions over the continental U.S. were compared with NO2 total tropospheric columns obtained from SCIAMACHY satellite-based sensor for July-August 2004. Two CMAQ simulations were performed, one with and one without lightning emissions. Simulated NO2 columns were mostly lower than observed, though highly correlated (R2=0.61-0.65) in the west, while in the eastern U.S., column amounts were comparable but had a lower correlation (R2=0.30-0.39). Comparison of NO2 columns by state found additional eastern states where simulated levels were lower than the satellite observations as well as most western states. Additional comparisons according to land use - "urban", "rural" and "rural-point" - found that NO2 total columns derived from satellite correlate well with simulated NO2 concentrations for "rural" regions but the correlation is lower for "urban" and "rural-point" regions. Simulated NO2 columns in Los Angeles are significantly lower than observed which may indicate a retrieval/analysis error, a bias in emission estimates specific to that region (or, conversely biases in the other regions), or modeling issues specific to that area. Lower correlations in "rural-point" regions are surprising with their emissions being viewed as relatively well known. Potential reasons for this discrepancy are 1) the transport of NOx out of the small satellite scan area and 2) insufficient time for conversion of NO to NO2 in power plant plumes. High correlation of "rural" regions is promising for estimating the following types of NOx emissions which is hard to capture otherwise: 1) area emissions that are sparse and poorly quantified, 2) lightning emissions and 3) prescribed or wildfire emissions. This work gives information on use of the satellite retrievals in data assimilation for regional air quality models and their potential to further improve the emission inventories by assessing the accuracy and consistency of current estimates. Data assimilation using satellite retrievals will also be performed for NOx emissions to identify errors in emission inventories which is key to developing effective environmental policies and improving our understanding of atmospheric processes.
A21B-0131
Investigation of NOx Emissions and NOx-related Chemistry in East Asia Using CMAQ- predicted and GOME-derived NO2 Columns
This study examined the estimation accuracy of NOx emissions over East Asia with particular focus on North China and South Korea due to their strong source (North China)-receptor (South Korea) relationship. In order to determine contributions of North China emissions to South Korean air quality accurately, it is important to examine the accuracy of the emission inventories of both regions. In this study, NO2 columns from the Models-3/CMAQ model simulations carried out using the 2001 ACE-ASIA emission inventory over East Asia were compared with the GOME-derived NO2 columns. There were large discrepancies between the CMAQ-predicted and GOME-derived NO2 columns in the fall and winter seasons. In particular, while the CMAQ-predicted NO2 columns produced larger values than the GOME- derived NO2 columns over South Korea for all four seasons, the CMAQ-predicted NO2 columns produced smaller values than the GOME-derived NO2 columns over North China for all seasons with the exception of summer. It is believed that there might be some estimation error in the NOx emissions as well as large uncertainty in NOx loss rates over North China and South Korea.Regarding the latter, this study further focused on the biogenic VOC emissions that were strongly coupled with NOx chemistry in East Asia. It was found that the rates of NOx loss determined by CMAQ modeling studies might be significantly low due to the possible overestimation of biogenic isoprene emissions during summer, particularly in China. A comparison between the CMAQ-predicted and GOME-derived NO2 columns indicated that the ACE-ASIA inventory has some uncertainties in NOx emissions over North China and South Korea, which can lead to some error in modeling the formation of ozone and secondary aerosols in South Korea and North China.
A21B-0132
Testing and Improving OMI Tropospheric NO2 Using Observations From the DANDELIONS and INTEX-B Validation Campaigns
Satellite observations of trace gases and aerosols are increasingly used to understand the effects of pollution on regional air quality and global climate change. Validation of these measurements is crucial for evaluating the quality of these novel data products, establishing their use in air quality monitoring and providing top-down constraints on emissions. We present a validation of tropospheric NO2 columns from the Ozone Monitoring Instrument (OMI) using measurements from the DANDELIONS and INTEX-B campaigns in 2006. These campaigns were unique because they covered a wide range of pollution scenarios and provided detailed information on the vertical distribution of NO2 (an important source of error in the OMI retrieval). During the Dutch Aerosol and Nitrogen Dioxide Experiments for vaLIdation of OMI and SCIAMACHY (DANDELIONS), tropospheric NO2 profiles were measured with a lidar over the highly polluted region of the Netherlands. During the Intercontinental Transport Experiment (INTEX-B), NO2 profiles were measured using laser induced fluorescence onboard an aircraft in a range of scenarios over the Gulf of Mexico. We examine how the observed profile shapes differ from the simulated profile shapes (from the 3-D chemistry transport model TM4) used in the OMI retrieval. From these comparisons, we determine an empirical error in the retrieval with respect to profile shape assumptions. We also present case studies related to planetary boundary layer growth in the Netherlands, pollution outflow in the Gulf of Mexico and the effects of using improved Mexico city terrain heights on the OMI NO2 product.
A21B-0133
Analyses of the concentration variation of total odd nitrogen species, nitric acid and particulate nitrate at Okinawa Island, Japan during the long-range transport from the Asian Continent
Recent emission of nitrogen oxides (NOx) shows rapid increase in the Asian Continent. NOx are transported and chemically transformed, and can affect the atmospheric environment in other regions. We are conducting continuous measurements of total odd nitrogen species (NOy), HNO3 and particulate nitrates at Cape Hedo, Okinawa, Japan, a remote region downwind from the Asian Continent in winter. The origin of air mass was classified in six groups, North China (CH1), Middle China (CH2), South China (CH3), Korea (KR), Japan (JP) and Pacific Ocean (PO), using backward trajectory analyses (NOAA, HYSPLIT). The averaged concentrations of NOy from the Asian Continent (CH and KR) were higher than those from PO and JP. This result indicates that NOy concentrations at Okinawa was affected by the long range transport of NOy from the Asian Continent. The variation of NOy and HNO3 concentrations was analyzed against the transport time. The maximum values of NOy decrease with the increase in the transport time. This must be attributable to the dilution of air mass and the deposition of NOy during the transport from the Asian Continent. Meanwhile, the concentration profile of HNO3 against the transport time shows a peak value around 40. The dependence of HNO3 to the transport time could be a result from the balance of HNO3 production and deposition. The HNO3 lifetime was estimated from the transport time dependence of HNO3. The detail will be discussed in the poster.
A21B-0134
Export of NOy from the United States during summer 2004
Previous studies suggest that U.S. anthropogenic nitrogen oxide (NOx) emissions have decreased in recent years in response to the U.S. EPA SIP call and that lightning NOx emissions over the United States are underestimated in current models. We examine the implications of these emission changes on the budget and export of reactive nitrogen (NOy) from the United States. The decrease in eastern U.S. power plant NOx emissions is estimated to have decreased total U.S. surface NOx emissions by 23% in our 2004 inventory compared to the 1999 U.S. EPA National Emissions Inventory. We increase the lightning NOx source over the northern mid-latitude continents by a factor of 10 and the fraction emitted into the free troposphere (FT) from 80% to 98%. In a simulation with these updated emissions, most NOx emitted in the model from the U.S. boundary layer (BL, below 800hPa) during July deposits as NOy (70%) while the rest is exported. This export ratio (30%) is at the high end of previous Eulerian studies (20-30%) due to our lower BL top and overestimate of PAN in the BL. The major export pathway for NOy from the United States is eastward (through 67.5W) in the FT, through which 15% of the NOx emitted (including lightning, aircraft and surface emissions) in the total column (surface to 200 hPa) is exported to the North Atlantic. From sensitivity experiments, we find that the export and burden of NOy respond less than proportionally to changes in either anthropogenic or lightning NOx emissions due to changes in NOy partitioning (with HNO3 contributing relatively more and PANs relatively less as emissions increase, and vice versa) and in the NOy lifetime (opposite sign of the emission change). Better constraints on the lightning NOx source are required to quantify accurately the export of anthropogenic NOy from the United States and to assess subsequent impacts of reductions in US anthropogenic emissions on air quality in downwind receptor regions.
A21B-0135
Assessing the uncertainty in the global distribution of atmospheric methane using AQUA/AIRS and the Global Modeling Initiative's CTM
Global observations from space will help to reduce the large uncertainties in the global budget of methane. In our work we identify the major areas of agreement and disagreement between global methane data collected from the Atmospheric Infrared Sounder (AIRS) instrument aboard NASA's AQUA satellite and NASA's Global Modeling Initiative's chemical transport model (GMI CTM). Our goal is to help in the evaluation of this relatively new data product and to identify its strengths and limitations for constraining the methane budget. We found major discrepancies between the model and observations in regions of deep convection, such as in South Asia, the Tibetan Plateau and the entire ITCZ, which may indicate a model deficiency in simulating convective transport or a retrieval issue with clouds. In addition, areas of high surface albedo with low cloud cover also show greater than 5% differences between model and observations. Examples of this issue are most obvious in northern high latitudes during boreal winter (snow) and east and west of South America over open ocean.
A21B-0136
MOPITT Version 4 Products for CO: Content, Format, and Validation
Observations from the Measurements of Pollution in the Troposphere (MOPITT) satellite instrument form a nearly continuous nine-year global record of tropospheric carbon monoxide. MOPITT radiance data are now being reprocessed into a new retrieval product. Following numerous analyses and developments in instrument modeling, radiative transfer modeling and retrieval algorithm design, the new Version 4 MOPITT product offers users (1) improved retrieval performance in both clean and heavily polluted atmospheres, (2) geographically- and seasonally-variable a priori, and (3) significantly reduced long-term drift. The diagnostic content of the MOPITT Level 2 product has also been enhanced for users' convenience. For example, the retrieval averaging kernels, which quantify the retrievals' vertical sensitivity, are now a standard diagnostic within the Level 2 product. We will highlight the major differences between the new Version 4 and previous Version 3 MOPITT products, in both content and format, and present validation results in the form of comparisons to CO in-situ profiles. Preliminary plans for the MOPITT Version 5 product will also be outlined.
A21B-0137
Chemical and Aerosol Signatures of Biomass Burning via Long Range Transport observed at Storm Peak Laboratory
The Desert Research Institute operates a high elevation facility, Storm Peak Laboratory (SPL), located on
the Steamboat Springs Ski Resort in Colorado at an elevation 3.2 km. During the spring of 2008, two field
projects were conducted at SPL; Storm Peak Cloud and Aerosol Characterization (SPACC) and a State of
Colorado Mercury Monitoring project. Measurements of gaseous elemental mercury (GEM), along with CO,
ozone and aerosol concentrations and aerosol size distributions will be presented from April 28 to July 1st
2008. This work focuses on specific case studies pertaining to long range transport events. Specifically,
high levels of GEM and CO will be presented from May 15, 2008. This data will be coupled with HYSPLIT
backtrajectories, chemical modeling via MOZART, and satellite imagery (MODIS) to present evidence that
Siberian wildfires impacted the air quality at Storm Peak Laboratory.
http://www.stormpeak.dri.edu
A21B-0138
Satellite observations of ozone and carbon monoxide from the Tropospheric Emission Spectrometer over Beijing and China between 2005-2008
We present seasonal variations in tropospheric ozone and CO vertical profiles from the TES instrument aboard the Aura satellite over Beijing between July 2007 and September 2008 and regionally averaged trends over China since December 2005. These observations were used in conjunction with visible MODIS imagery, OMI NO2, and meteorological re-analyses to investigate the impact of meteorological and photochemical conditions upon ozone production. Preliminary results show peak ozone mixing ratios during July 2007 and 2008 were in excess of 250 ppbv within the lower troposphere and upper boundary layer; and background concentrations above Beijing remain consistently higher than other urban mid-latitude environments.
A21B-0139
Ice Core Data of Atmospheric Carbon Monoxide Over Antarctica During The Last 170 Years
The importance and interest for reconstructing past CO concentrations arises from its significant role on the chemistry of the troposphere. As the major sink for hydroxyl radicals (OH), carbon monoxide is considered to regulate the oxidative capacity of the atmosphere. CO also has a close link with methane which is a main source of CO especially in Southern Hemisphere. Past atmospheric CO concentration will help better understand past trend of the atmospheric oxidative capacity. Past isotopic data of CO will assist in determining the various sources and sinks in the past and their historic relative magnitudes. However, little information about past CO is reported due to the difficulties of measuring atmospheric CO in the ppbv range. Our study on CO in Antarctic ice cores helps determine the past trend of atmospheric oxidative capacity and relationship between CO and methane. In this study, we present both the isotopic data and concentration measurements of atmospheric CO in D47 ice cores. Ice core samples were prepared based on wet extraction method in LGGE, France. Measurements were made with a cryogenic vacuum extraction system and continuous-flow isotopic ratio mass spectrometer (CF-IRMS) in Stony Brook University, NY. 12 D47 ice core samples have been measured for both CO mixing ratio and isotopic ratios. The range of the depth is from 69m to 109m, corresponding to a range of gas age from 1829 AD to 1941 AD. It is found that CO level in the above gas age range is around 55-60ppbv and doesn't change much during this time frame. d13C (VPDB) of CO is around -28 per mil and no apparent trend of d13C is found. More isotope data are needed to show us a clear trend, especially for ice cores extending back to pre-industrial time. As for d18O, our data show very heavier d18O values. Usually high d18O values indicate foreign CO, but due to the relatively constant CO mixing ratio, this possibility can be eliminated. If there is no foreign CO, there may be some unexpected processes such as isotope exchange between oxygen in CO and oxygen in other compounds in ice, some growth process and loss process at the same time which we don't know. Or the worst is that CO in ice is corrupted in an unpredictable way. Testing with other Antarctic ice cores will help us figure this out.
A21B-0140
An Analysis of the Processes Controlling the Distribution and Interannual Variability of Carbon Monoxide and Ozone in the Tropical Troposphere Using TES and MLS Data and Global Models.
Analysis of observations from the Tropospheric Emission Spectrometer and the Microwave Limb Sounder on the Aura satellite shows the large scale spatial and vertical distribution of carbon monoxide (CO) and ozone in the tropical troposphere in unprecedented detail. The four years of these data also reveal interannual variability that is largest over Indonesia (as a result of ENSO and variations in biomass burning), but is significant elsewhere. Here we use these data, along with in-situ observations, to first evaluate global model simulations of CO and ozone, and then to investigate the causes of any discrepancies between model and observations, and finally to diagnose the causes of interannual variability, with a series of sensitivity simulations. We focus in particular on emissions from biomass burning, emissions of NOx from lightning, and variability in dynamics. This study uses the GMI-Combo and GEOS-Chem models. We acknowledge useful discussions with the TES, MLS, and GMI science teams.
A21B-0141
Comparison of Total OH Reactivity Measurement Methods in Ambient Air between a Comparative Reactivity Method using PTR-MS and a LASER Technique
OH radical plays an important role in atmospheric chemistry. OH reactivity measurement is essential to understand atmospheric chemical reaction processes. We have developed LASER technique to measure OH reactivity. This system requires both pump and probe lasers and high vacuum system. We have to pay a lot of efforts to bring the instrument in the field for ambient observation. Therefore we have developed a comparative reactivity method for measuring total OH reactivity recently. Since this method does not need a large space and complicated devices, it makes relatively easy to measure OH reactivity anywhere. The result of this non-laser OH reactivity measurement was compared with that of laser pump and probe technique as conducted an intensive field measurement of sub-urban air in Tokyo, July 2008. In comparative reactivity method, a regent species (X), which is ideally not present in ambient air, is introduced into the flow tube reactor and its concentration (C1) is monitored by a suitable detector under nitrogen atmospheric condition. A constant amount of OH radicals is then introduced into the flow tube to react with X under either nitrogen atmosphere (the concentration of X became C2) or ambient air (the concentration of X became C3). Total OH reactivity can be calculated by comparing C1, C2 and C3. OH radicals were produced in the photolysis of water vapor by a UV lamp. In our experiment, Pyrrole is selected as X and PTR-MS is used as a detector. The concentrations of NO, NO2, CO, SO2 were also measured. In some case, the two methods indicated some differences, for example, OH reactivity of 10 to 30 s-1 measured by LASER technique while the comparative reactivity method showed the value of only 5 to 12 s-1.This reason appears to be humidity dependence of PTR-MS sensitivity. Good agreements, for trends and absolute values, were found for comparison between the two methods during another day of experiment where both methods reveal OH reactivity ranging between 10 and 25 s-1. Despite these uncertainties need more scrutiny, it was suggested that comparative reactivity method allows reasonably to measure OH reactivity in ambient air easily without these interferences.
A21B-0142
OH Yields from Gas-Phase Ozonolysis of Isoprene
Environmental chambers are an important part of an integrated and multifaceted approach to understanding chemical processes in the atmosphere, by bridging the gap between laboratory measurements of individual elementary reactions and the complexity of the real atmosphere. The University of Leeds HIRAC (Highly Instrumented Reactor of Atmospheric Chemistry) chamber is a 2 m3 stainless steel vessel capable of operating at a variety of temperatures and pressures, enabling wide ranging kinetics experiments [D.R. Glowacki et al., Atmos. Chem. Phys., 7,5371,(2007)]. Ozone-alkene reactions are a non-photolytic source of OH, HO2 and RO2 radicals and are a significant source of these radicals in urban and rural air. We have used four different methods to measure OH yields in the HIRAC chamber. These are (1) laser- induced fluorescence at low pressure (FAGE) (detection limit of ~106 molecule cm-3); which provides a direct, calibrated measurement of the OH radical concentration. (2) An indirect method to measure OH yields by use of an OH radical scavenger (cyclohexane) producing stable products (cyclohexanol and cyclohexanone), the concentrations of which allow OH yields to be determined after suitable calibration. (3) A second indirect method utilises 1,3,5-trimethylbenzene (TMB) as an OH tracer, which is consumed by reaction with OH radicals. Analysis of the diminution in concentration of TMB allows the estimation of OH radical production yields. (4) Also a kinetic study was utilised, in which the decay of isoprene follows pseudo-first order kinetics using a 10 fold excess of ozone over alkene. The decay rate of isoprene was monitored using gas chromatography (GC) and FTIR, and was found to be exponential in all cases. From the decrease of the effective rate constant upon the addition of cyclohexane, the OH yield was determined. These 4 different techniques were used to measure the OH yield of O3 + isoprene. The three indirect techniques have been used to determine OH yields for ozone + isoprene of 0.267 ± 0.024, 0.265 ± 0.020 and 0.253 ± 0.026 for detection by OH scavenger, kinetic study and OH tracer, respectively. The reaction between O3 and isoprene has been studied by the direct detection the OH concentrations using FAGE, with excellent precision. A numerical model based on the Master Chemical Mechanism (MCM), with the OH yield as a variable parameter, was used to calculate the OH concentration, and a best fit to the OH FAGE concentration data, gave a yield of 0.255 ± 0.022 was determined. These techniques were then utilised to determine a pressure dependence of the OH yield for ozonolysis of isoprene.
A21B-0143
Total OH Reactivity in Ambient Air Measured in the Pearl-River Delta in China 2006
We have developed a new instrument for the measurement of the total atmospheric OH reactivity, which is defined as the pseudo-first order loss-rate coefficient of OH, resulting from the reactions of OH with atmospheric trace gases like VOCs, CO, NOx etc. The instrument is capable of measuring the lifetime of OH (i.e., the reciprocal OH reactivity) in ambient air, by using a pulsed UV-pump laser-induced fluorescence (LIF) probe technique. The measurement range covers reactivities between 1 s-1 to about 150 s- 1, corresponding to conditions from very clean to very polluted environments, with a time resolution of 1-3 min. Here we present measured OH reactivities which were collected during the PRIDE-PRD 2006 photochemistry field campaign in the densely populated Pearl River Delta (PRD) in South-China, and present an analysis of the total burden of reactive VOCs encountered at PRD.
A21B-0144
Ambient measurements of OH and HO2 radicals and the OH reactivity in and above the Borneo Rainforest
Ground-based measurements of OH, HO2 and the OH reactivity have been made as part of the OP3 project that took place at the Bukit Atur Global Atmospheric Watch station in the Danum Valley forest conservation area in Sabah, Borneo in 2008. The project consisted of two intensive measurement periods in April and July. Aircraft measurements of OH and HO2 above the ground site were also performed and preliminary data will be presented. The OH and HO2 radicals exhibit a distinct diurnal profile, broadly following the j(O1D) profile that was measured simultaneously (daytime [OH] ~ 2 - 5 x 106 molecule cm-3, [HO2] ~ 1 - 1.5 x 108 molecule cm-3). NO, which peaked in the early morning hours ([NO] ~ 100 pptV) and isoprene, which peaked in the afternoon ([isoprene] ~ 2 - 5 ppbV) were found to influence the OH profile. Both OH and HO2 persisted into the night and were detectable even after j(O1D) had fallen to zero (nighttime [OH] ~ 2.5 x 105 molecule cm-3, [HO2] ~ 2 x 107 molecule cm-3), suggesting night-time radical sources. The OH reactivity tracked the isoprene concentration, exhibiting maximum reactivity just after midday when isoprene levels peaked. Zero dimensional models, using a variety of mechanisms, have been used to predict the [OH], [HO2] and the OH reactivity that were observed. The models, constrained with measured OH sources and sinks, are used to test the hypothesis that OH is recycled from isoprene oxidation in this low NOx environment
A21B-0145
The International Halocarbon in Air Comparison Experiment (IHALACE): first results.
and the Ihalace team Atmospheric measurements of halocarbons and related trace gases are being conducted by a number of groups in order to assess sources and sinks and to help verify the effectiveness of international treaties, such as the Montreal Protocol on Substances that Deplete the Ozone Layer. While measurement precision is often very good, many of these measurements are performed on independent calibration scales, and there have been few interlaboratory comparisons to assess absolute uncertainties and scale differences. Thus, the prospect of combining data sets obtained from different groups to achieve better spatial and temporal coverage is subject to unknown errors. Further, there is no routine international project for comparison or data quality management such as that provided for carbon dioxide and methane under the WMO Global Atmosphere Watch programme. In order to assess the differences in measurements preformed by different laboratories, the International Halocarbon in Air Comparison Experiment (IHALACE) was designed. In this experiment, two sets, each consisting of three gas cylinders containing natural or modified continental background air, were prepared and circulated among 21 participating laboratories. Each laboratory performed the measurements and submitted the data to two independent referees. Although the primary focus was on chlorofluorcarbons and related compounds, other trace gases such as N2O, SF6, and CH4 were also included. We present the experimental set-up, together with results (in an anonymous format) to show the level of agreement that is reached when mixing ratios in air samples are derived by different laboratories.
A21B-0146
Climate and Air Quality Impact of a Hydrogen Economy
It is imperative to fully analyze the risks and benefits of policy decisions before they are implemented, particularly given the past adverse global impacts of anthropogenic emissions, e.g., CFCs and their impact on stratospheric ozone. An interesting "what if" question is what would be the potential environmental impacts if the U.S. were to transition from a fossil fuel based energy system to a society heavily dependent on hydrogen based transportation. We focus on systematically examining and identifying possible near- and long-term ecological, environmental, and climate effects of the large-scale production and use of hydrogen in transportation and power applications examining both the direct and indirect effects. We use the IPCC 2050 A1FI SRES emissions scenario as a baseline and develop alternative H2 adoption emissions scenarios as perturbations to this baseline. The perturbation scenarios include various combinations of enhanced H2 emissions and reductions of VOC, NOx, and SOx emissions. Three-dimensional CAM-Chem model simulations suggest that for a complete transition to hydrogen-based energy and transportation systems the tropospheric H2 burden would increase substantially, as much as 7.7 times the baseline. There would also be significant decreases in tropospheric OH and ozone. Summer mean surface ozone concentrations over the continental U.S. would decrease by as much as 35 ppb, largely due to the net reduction in emissions of nitrogen oxides and hydrocarbons. Simulations also suggest that these results are sensitive to the dependence of soil H2 uptake on atmospheric H2 concentrations
A21B-0147
Field measurements of ammonia concentrations in Edinburgh, Scotland between August- September 2008: a comparison between chemical ionization mass spectrometric (CIMS) and quantum cascade laser (QCL) techniques
Measured ammonia concentration time series are compared between two different techniques (CIMS and QCL) over a 10 day period. The field site was situated in Edinburgh, Scotland. Conditions ranged from rainy and cold (~9°C) to warm and dry (~22°C). During the warmer period, urea was spread on the field site --- urea hydrolyzes to produce artificially high concentrations of ammonia. These contrasting conditions afforded a broad range of ammonia concentrations over which to compare the instruments. Comparisons are found to be in general good agreement, with most local changes in ammonia concentration being identified by both instruments at similar times and magnitudes. Where discrepancies occur, they are attributable to differences in inlet design; i.e. length, throughput, pressure and temperature, and possibly spatial separation. These differences are investigated with a series of laboratory uptake experiments into the effects of inlet temperature, pressure, length and material type. Each of these parameters is found to be important: temperature improves instrument response time, whereas pressure, length and material type were found to affect signal magnitude. Although heating the inlet was found to be advantageous, dissociation of ammonium nitrate may represent a spurious contribution to measured ammonia concentrations in the gas phase. With this in mind, the thermodynamics of ammonium nitrate dissociation was probed using Knudsen effusion mass spectrometry (KEMS). Further investigations were made by introducing a known concentration of ammonium nitrate aerosol into a heated inlet to investigate whether ammonium nitrate can be dissociated in typical field inlet conditions.
A21B-0148
Land use Change, CO2 Suppression, and Anthropogenic Forcing - Impacts on Isoprene and the Chemical Composition of the Troposphere
As the main source of volatile organic compounds (VOCs), the terrestrial biosphere plays a key role in tropospheric chemistry processes. Isoprene emissions, which contribute to more than half of biogenic VOC emissions, are controlled by climate conditions (temperature, radiation), vegetation characteristics (plant type, leaf area, soil moisture), as well as by the chemical composition of the atmosphere (impact of CO2 variation on plant emission capacity, for example). In the future, changes in climate, land-use, vegetation distribution and atmospheric CO2 concentrations are likely to affect significantly the isoprene emission level and, consequently, could have strong impact on the chemical composition of the atmosphere. In this study, a biogenic emission scheme based on recent knowledge is used to provide estimates of isoprene emissions for the present-day and the future (2100) using climate forcing from the Unified Model and vegetation characteristics calculated by the Sheffield Dynamic Global Vegetation Model. The impact of changes in isoprene emission on the chemical composition of the troposphere is then investigated using the UK Chemistry and Aerosol community model, with special attention paid to ozone production and loss. A suite of integrations evaluate relative contributions of land use change, CO2 suppression of isoprene emissions, and anthropogenic emissions scenarios to future changes in the oxidising capacity of the atmosphere.
A21B-0149
Ethane Seasonality and Incorporation Into Firn at Summit, Greenland
Ethane, the second most abundant hydrocarbon in the atmosphere, plays an important role in tropospheric ozone and hydroxyl radical chemistry. An atmospheric history of ethane would improve the current inadequate understanding of fluctuations of ethane and its sinks and sources through time. A twelve year time-series dataset from GC/MS measurements of flasks filled with surface air at Summit, Greenland show no overall trend except for a modest increase in the last two years. The results of two firn air samplings from 2006 and 2008 are compared with the surface time-series data to investigate the fidelity of the firn air ethane record. There is strong evidence that the firn column at Summit, Greenland is a genuine archive of the history of atmospheric ethane. A short timescale study of ethane diffusion in the firn layer improved a standing model of this gas's incorporation into the firn, facilitating the determination of ethane levels in recent decades. The preliminary results support the earlier findings that the atmospheric levels of this gas dropped 25-30% over the last 30-40 years of the 20th century.
A21B-0150
Satellite Observations of Tropospheric Ammonia
Global high-spectral resolution (0.06 cm-1) nadir measurements from TES-Aura enable the simultaneous retrieval of a number of tropospheric pollutants and trace gases in addition to the TES standard operationally retrieved products (e.g. carbon monoxide, ozone). Ammonia (NH3) is one of the additional species that can be retrieved in conjunction with the TES standard products, and is important for local, regional, and global tropospheric chemistry studies. Ammonia emissions contribute significantly to several well-known environmental problems, yet the magnitude and seasonal/spatial variability of the emissions are poorly constrained. In the atmosphere, an important fraction of fine particulate matter is composed of ammonium nitrate and ammonium sulfate. These particles are statistically associated with health impacts. When deposited to ecosystems in excess, nitrogen, including ammonia can cause nutrient imbalances, change in ecosystem species composition, eutrophication, algal blooms and hypoxia. Ammonia is also challenging to measure in-situ. Observations of surface concentrations are rare and are particularly sparse in North America. Satellite observations of ammonia are therefore highly desirable. We recently demonstrated that tropospheric ammonia is detectable in the TES spectra and presented some corresponding preliminary retrievals over a very limited range of conditions (Beer et al., 2008). Presented here are results that expand upon these initial TES ammonia retrievals in order to evaluate/validate the retrieval results utilizing in-situ surface observations (e.g. LADCO, CASTNet, EPA /NC State) and chemical models (e.g. GEOS-Chem and CMAQ). We also present retrievals over regions of interest that have the potential to help further understand air quality and the active nitrogen cycle. Beer, R., M. W. Shephard, S. S. Kulawik, S. A. Clough, A. Eldering, K. W. Bowman, S. P. Sander, B. M. Fisher, V. H. Payne, M. Luo, G. B. Osterman, and J. R. Worden, First satellite observations of lower tropospheric ammonia and methanol, Geophysical Res. Letters, 35, L09801, doi:10.1029/2008GL033642, 2008.
A21B-0151
Global NMVOC fluxes inferred from SCIAMACHY formaldehyde columns through 2003-2006
Formaldehyde (HCHO) columns retrieved from the SCIAMACHY satellite instrument through 2003 to 2006 are used as top-down constraints to derive updated global biogenic and biomass burning flux estimates for the non-methane volatile organic compounds (NMVOCs) precursors of formaldehyde. Our interest is centered over regions experiencing strong emissions, and hence exhibit a high signal-to-noise ratio and lower measurement uncertainties. The HCHO dataset used in this study has been recently made available to the community and complements the long record of formaldehyde measurements from the GOME instrument. HCHO columns are simulated by the IMAGESv2 global chemistry- transport model. The model is driven by the Global Fire Emission Database (GFED) version 1 and 2 inventories for vegetation fires, and the MEGAN-ECMWF isoprene emission database. The adjoint of the model is implemented in a grid-based framework within which both biogenic and pyrogenic emission fluxes are derived at the model resolution. Two inversion studies are conducted using either the GFEDv1 or GFEDv2 as prior for the pyrogenic fluxes. The updated NMVOC emissions are presented and compared with results from previous studies, whereas a number of sensitivity experiments are conducted in order to assess the impact of the inversion setup on the robustness of the inferred fluxes.
A21B-0152
Satellite Observations of Tropospheric Composition: 4+ years of Tropospheric Emission Spectrometer (TES) Retrievals
Launched in July 2004 on the AURA satellite, TES has been making almost continuous global and regional
measurements of key tropospheric species such as ozone, carbon monoxide, methane and water vapor ever
since. Recently, it has become clear that ammonia and methanol can be added to the list. Temperature
profiles, ozone radiative forcing and HDO/H2O ratios are also routinely generated.
The poster will display highlights of these measurements and some future prospects as the primary mission
draws to a close.
This work was carried out, in part, at the Jet Propulsion Laboratory, California Institute of Technology,
Pasadena, under contract with the National Aeronautics and Space Administration.
http://tes.jpl.nasa.gov
A21B-0153
Retrieval of tropospheric trace gas profiles with satellite infrared radiometer
The quantitative measurement of the atmospheric trace gases is one of the important technologies for understanding the global environmental changes. The retrieval of ozone in troposphere was investigated with the satellite hyperspectral infrared measurement data in this study. Firstly, we examined the possibility of ozone retrieval by using simulated radiance data and the initial guess. The climatological a priori was taken from ECMWF ERA40 and emissivity data from ASTER Spectral Library. Especially, we made land-cover classification map corresponding to ASTER Spectral Library using MODIS albedo product. Secondary, we carried out the retrieval test using the spectral radiances measured by Tropospheric Emission Spectrometer (TES), which was launched on NASAfs EOS AURA satellite in July 2004, in order to validate the appropriateness of the retrieval.
A21B-0154
Comparing OMI and AIRS Retrievals Against AIRPACT-3 Forecasts for the Pacific Northwest
The AIRPACT-3 regional air quality forecast system, which utilizes the MM5/SMOKE/CMAQ modeling suite, runs nightly predicting air quality for the Pacific Northwest. AIRPACT has been evaluated periodically against surface monitor data for ozone and PM2.5. In a NASA-funded project, satellite measurements of air quality in the Pacific Northwest are being compared to AIRPACT results to: 1) provide feedback on the accuracy of the emissions inventory used by AIRPACT and 2) explore how satellite retrievals may be used operationally for initialization and validation. Measurements of tropospheric NO2 from OMI (Ozone Monitoring Instrument) as well as CO from AIRS (Atmospheric InfraRed Sounder on Aqua) are compared to forecast results. Monthly average comparisons over a 20 month period are examined for NO2 over the entire domain to identify spatial anomalies in the emissions inventory. Day-to-day and month-to-month trend comparisons around urban areas are analyzed to evaluate relative model response. AIRPACT profiles are compared to satellite profiles at individual urban points and the OMI NO2 averaging kernels are also used to calculate columns independent of the assumed tropospheric profiles used in the retrieval algorithms. AIRPACT also gets wildfire emissions from the Forest Service BlueSky project; satellite column abundances of NO2 and CO are used to evaluate these wildfire emissions over the past two summers. Finally, a design model for planned assimilation is presented for specific satellite products, indicating their expected temporal frequency of utility (i.e. daily, monthly, etc.) and the model stage (i.e. initial conditions, boundary conditions or model emissions) of their assimilation into the AIRPACT-3 forecast system.
A21B-0155
Atmospherically and climatologically relevant emissions from Mumbai, India
Virtually all population growth during the next 30 years will occur in urban areas. As Asian, African, and South American urbanization accelerates in the coming decades, the human influence on the earth system will become increasingly noticeable. Mumbai (formerly Bombay), India is a rapidly growing tropical megacity with an estimated population of 18.1 million persons and with a very high population density (25,041 km-2). Because of these urbanization trends and the resulting potential for large-scale environmental impact, we measured a range of gas phase chemical compounds, including oxidant forming and toxic VOCs, CO, NOx and O3 on multiple days during the 2008 dry season across the Mumbai metropolitan area. These compounds influence the formation of photochemical oxidants, dictate the budgets and makeup of exported gases and aerosols, influence radiative properties of the atmosphere, and perturb human health and other biological systems. We will compare our results from Mumbai to several other large urban areas in the United States and Mexico.
A21B-0156
Accurate Calculations of Global and Local Radiative Forcing due to Tropospheric Ozone and Nitrogen Dioxide
Since the launch of the A-train constellation of satellites in an afternoon polar orbit, much has been learned about the global distributions of the radiatively active tropospheric gases ozone and nitrogen dioxide. Both gases absorb radiation in the shortwave. In addition, tropospheric ozone is an important greenhouse gas. From A-train observations, we have also made great progress in understanding how clouds affect gaseous absorption. By combining information from different A-train sensors (cloud optical depth and surface albedo from MODIS, tropospheric ozone from the combination of OMI and MLS, and the optical centroid cloud pressure from OMI), we have accurately computed the radiative forcing due to tropospheric ozone and nitrogen dioxide on a global daily basis. We can therefore accurately assess the cloud effects on the radiative forcing. These results may be used to check and place constraints on calculations provided by models that are the primary tool for assessing the radiative forcing due to anthropogenically-produced changes in tropospheric ozone (e.g., as in the 2007 Intergovernmental Panel for Climate Change report).
A21B-0157
Development of Negative Ion Proton Transfer Reaction Time-of-Flight Mass Spectrometry (NI-PTR TOFMS) for the Measurement of Gas Phase Acids in the Troposphere
We report on the progress and feasibility tests of an on-line time-of-flight (TOF) technique for negative ion proton transfer reactive mass spectrometry (NI-PTRMS) for the measurement of trace gas phase carboxylic acids. Acetate ions are produced via alpha particle ionization of acetic acid through a polonium-210. The target carboxylic gases undergo proton transfer reactions with the acetate ions due to the affinity differences. This technique has the potential for improvement in mass resolution as well as shorter integration periods which lead to faster measurements with greater sensitivity. We report on initial instrument sensitivity, calibrations, and clustering effects of some known gases as well as some carboxylic acids for some comparisons with recent negative-ion proton-transfer chemical-ionization mass spectrometry (NI-PT-CIMS) results. This work is supported in part by both NOAA (Award NA06OAR4810187) and NSF (award 0803016).
A21B-0158
Development and Validation of a Novel Gas Analyzer for Simultaneous Measurements of Methane, Carbon Dioxide and Water Vapor in Ambient Air at 20 Hz
Methane has increased significantly with human population levels. Pre-1750 ice core data indicates that pre- industrialization levels were about 700 ppbv, while current levels are over 1750 ppbv. In current budget estimates of atmospheric methane, major contributors include both natural (wetlands) and anthropogenic sources (energy, landfills, ruminants, biomass burning, rice agriculture). The strengths of these sources vary spatially and temporally. Estimates of emissions from wetlands are also uncertain due to the extreme variability of these ecosystems. Because methane lifetime is relatively long (8.4 years), atmospheric variations in concentration are small and accuracy in measurement is important for understanding spatial and temporal variability. Atmospheric concentrations of carbon dioxide and methane rose sharply in 2007. Global CO2 climbed by 0.6 percent, or 19 billion tons, in 2007. Methane increased by 27 million tons after nearly a decade with little or no increase. Atmospheric CO2 levels currently stand at 385 ppmv, or about 38 percent higher than pre- industrial levels and the rise in CO2 concentrations has been accelerating since the 1980s when annual increases were around 1.5 ppm per year. Last year the increase was 2.4 ppm. We report on the development, application and independent performance characterization of a novel gas analyzer based on cavity-enhanced laser absorption spectroscopy. The Analyzer provides simultaneous measurements of methane, carbon dioxide and water vapor in ambient air in the field for applications that require high data rates (eddy correlation flux), wide dynamic range (e.g., chamber flux and other applications with concentrations that are ten times typical ambient levels or higher) and highest accuracy (atmospheric monitoring stations). The Analyzer provides continuous measurements at data rates up to 20 Hz and with replicate precision of 1 ppbv for methane (1 second measurement time), 0.2 ppmv for carbon dioxide (1 second measurement time) and 100 ppmv for water vapor (1 second measurement time). The stability of the instrument allows for reliable averaging over longer periods for applications that require even higher accuracy and precision.
A21B-0159 INVITED
Trends and seasonal cycle of the tropospheric methane observed and modeled over Siberia
We analyzed 12 years of atmospheric methane data observed over West Siberia and compared with models of atmospheric transport and chemistry. The observational data were obtained by flask sampling and laboratory analysis. The samples were taken at the altitude range of 0.5 to 7 km once a month near Surgut and Novosibirsk. The purpose of this study was to compare simulated concentration time series with observed ones is order to evaluate existing surface methane emission estimates for the region. We conducted model simulations with three different chemical tracer transport models using seasonally varying methane emissions (without inter-annual variability). In the lower troposphere, seasonal cycle and trends are obscured by large synoptic scale variability, exceeding seasonal cycle amplitude and inter-annual variability. To reduce the effect of the variability we use multi-year average seasonal cycle in the comparison between models and observations. Observations and models suggest the methane concentration in lower troposphere is significantly different from the free troposphere in response to regional emissions. There is an indication of the large emissions in late summer in the observed seasonal cycle over Surgut. To improve a seasonal cycle fit we need improved surface methane flux models, properly accounting for amplitude and seasonality of emissions.