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Measurements Of Pollution In The Troposphere (MOPITT) GroupMOPITT Group Members:
Summary of Activities:MOPITT Operational Production of Carbon Monoxide Data
The daily operational processing of Measurement Of Pollution In The Troposphere (MOPITT) instrument raw counts into the final retrieved geophysical products, delivery of products to NASA for free public access, and user education and support, constitutes a major service to the scientific community. MOPITT is also unique in having produced the only validated global CO data product available to the community. Scientific results have been presented worldwide at numerous scientific meetings and show a documented strong presence on the Internet. MOPITT data distribution, publications, literature citations, and conference presentations are all showing strong upward trends, indicating mounting demand and scientific interest. Other sectors of government have shown increasing interest in the way in which global observations of pollution might provide useful information with respect to air quality (EPA and NOAA) and agricultural production (NARSTO and USDA).
The MOPITT data processing algorithms continue to be developed for the next data version 4. Enhancements will include: (1) a new forward model with improved description of the MOPITT gas correlation cells; (2) a new description of the retrieval a priori surface emissivity ; (3) a new seasonally and geographically variable CO retrieval a priori; and (4) the use of an assumed log-normal variability for CO volume mixing ratio in the new retrieval algorithm. In a continued effort to provide the best possible data product several other important data quality issues have been identified and addressed. These including mitigating data quality issues identified in the NCEP water vapor product which is used by the MOPITT operational algorithm and analyzing the effect of vertical correlation length on the MOPITT retrievals using statistics generated from in situ field data.
Satellite observed pollution from southern hemisphere biomass burning
Biomass burning is a major source of pollution in the tropical southern hemisphere, and fine mode carbonaceous particles are produced by the same combustion processes that emit CO. These emissions have been examined with data from the Terra satellite, CO profiles from MOPITT instrument and fine mode aerosol optical depth (AOD) from the Moderate-resolution Imaging Spectroradiometer (MODIS). The satellite measurements were used in conjunction with calculations from the MOZART chemical transport model to examine the 2003 Southern Hemisphere burning season with particular emphasis on the months of peak fire activity in September and October.
Pollutant emissions follow the occurrence of dry season fires, and the temporal variation and spatial distributions of MOPITT CO and MODIS AOD are similar. The outflow from Africa and S. America was examined with emphasis on the impact of these emissions on clean remote regions. Comparisons of MOPITT observations and ground-based interferometer data from Lauder, New Zealand , Figure 1, indicate that intercontinental transport of biomass burning pollution from Africa often determines the local air quality. The correlation between enhancements of AOD and CO column for distinct biomass burning plumes is very good with correlation coefficients greater than 0.8. A method was developed using MOPITT and MODIS data for estimating the emission ratio of aerosol number density to CO concentration that could prove useful as input to modeling studies. Investigations were also made of plumes from African fires following export into the Indian Ocean , and comparisons of the MOPITT and MODIS measurements were used as a way of estimating the regional aerosol lifetime. Vertical transport of biomass burning emissions was also examined using CO profile information. Low altitude concentrations are very high close to source regions, but further downwind of the continents vertical mixing takes place and results in more even CO vertical distributions. In regions of significant convection, particularly in the equatorial Indian Ocean , the CO mixing ratio is greater at higher altitudes, indicating vertical transport of biomass burning emissions to the upper troposphere.
An inverse modeling study has also been performed for constraining biomass burning, anthropogenic, biogenic direct CO sources as well as CO produced from isoprene over South America for the year 2004. The biomass burning source has been estimated as 80 Tg CO yr -1 which accounts for close to 30% of the global biomass burning emissions and reflects the importance of South American biomass burning sources. No robust constraint could be put on biogenic, anthropogenic and isoprene sources, because the contributions for these are within the range of the uncertainties associated with observations and model results. However, the study reveals the importance of CO produced from isoprene in regional and also total CO budgets and thus the need for improved techniques for constraining isoprene emission inventories.
Participation in the INTEX-B field campaign
Interaction with the ongoing satellite measurements programs is an important goal of the NASA INTEX-NA field program. The MOPITT instrument has now been making global measurements of the tropospheric CO distribution for 6 years, and is in a unique position to provide valuable support during field campaigns. Remote sensing of CO directly addresses the scientific questions motivating the INTEX-NA strategy and deployments, and measurement of this gas is rated as being mission critical. CO is an important trace gas in tropospheric chemistry due to its role in determining the atmospheric oxidizing capacity, as an ozone precursor, and as an indicator and tracer of both natural and anthropogenic pollution arising from incomplete combustion. The satellite perspective provides the more general temporal and spatial context to the aircraft and ground-based measurements during the subsequent scientific analysis.
Based on previous experience of providing separate satellite data and model chemical forecasts during field campaigns, it was apparent that individually each of these tools had drawbacks for campaign flight planning purposes. The satellite data for CO only provide a snap-shot of plumes in the recent atmosphere and lack predictive capability in a changing atmosphere, whereas chemical transport models ( CTMs ) usually only provide a climatological description which may not be an accurate representation of actual conditions. A chemical assimilation of several days of satellite data into the CTM to initialize the forecast stage overcomes both of these concerns, Figure 2, and was the approach used by the ACD MOPITT/MOZART team for the INTEX-B flight planning support.
Prior to the start of the INTEX-B campaign, a new MOPITT/MOZART CO data assimilation system was developed. This had the following features: near-real-time MOPITT retrievals, daily and multi-day maps of the MOPITT CO distributions, biomass burning emission estimates based on satellite fire counts, CO tracer forecasts for identifying the sources of CO plumes that were observed in the MOPITT satellite data, and a web presence with mapped CO fields and “curtain” plots for easy data access. The MOPITT/MOZART team had a representative in the field to participate in flight planning for each phase of the INTEX-B operations. In addition, team members at NCAR maintained the dedicated NRT MOPITT data processing, the MOZART assimilation and tracer runs, data processing and graphical design, and website management. Support was also provided to the MIRAGE Mexico City campaign.
Measurements of CO made as part of three aircraft experiments during the summer of 2004 over North America have also been used for the continued validation of the CO retrievals from MOPITT. Vertical profiles measured during the NASA INTEX-A campaign, designed to be coincident with MOPITT overpasses, as well as measurements made during the COBRA-2004 and MOZAIC experiments, provided valuable validation comparisons. On average, the MOPITT CO retrievals are biased slightly high for these North America locations. While the mean bias differs between the different aircraft experiments (e.g., 7.0 ppbv for MOZAIC to 18.4 ppbv for COBRA at 700 hPa ), the standard deviations are quite large, so the results for the three data sets can be considered consistent. On average, it is estimated that MOPITT is 7-14% high at 700 hPa and ~3% high at 350 hPa .
Southern Hemisphere Carbon Monoxide Inter-annual Variability and the Response to Climate Observed by Terra/MOPITT
The CO emitted by the annual biomass burning in the tropical southern hemisphere (SH) is an excellent tracer of tropospheric transport due to its medium lifetime. CO is also one of the few tropospheric trace gases currently observed from satellite and this provides long-term global measurements. The 6 year CO data record from the MOPITT instrument was used to examine the inter-annual variability of the SH CO loading and show how this relates to climate conditions which determine the intensity of fire sources. The MOPITT observations show an annual austral springtime peak in the SH zonal CO loading each year with dry-season biomass burning emissions in S. America, southern Africa, the Maritime Continent, and northwestern Australia. Although fires in southern Africa and S. America typically produce the greatest amount of CO, the most significant inter-annual variation is due to varying fire activity and emissions from the Maritime Continent and northern Australia . This variation in turn correlates well with the El Nino Southern Oscillation precipitation index, Figure 3. Between 2000 and 2005, emissions were greatest in late 2002 and an inverse modeling of the MOPITT data using the MOZART chemical transport model estimates the southeast Asia regional fire source for the year August 2002 to September 2003 to be 52 Tg CO. Comparison of the MOPITT retrievals and NOAA surface network measurements indicate that the latter do not fully capture the inter-annual variability or the seasonal range of the CO zonal average concentration due to biases associated with atmospheric and geographic sampling.
Figure 1. Mean distribution of MOPITT CO total column for October 1-9, 2003 (a), and MOPITT and ground-based FTIR CO total column measurements during 2003 at Lauder, New Zealand (b). This clearly shows the impact of long-range transport of biomass burning pollution from Africa on the normally clean air over New Zealand .
Figure 2: MOPITT NRT 700 hPa CO composite distribution for 20-22 April (above) and corresponding assimilation in the MOZART CTM (below). Note that plumes in the data are reproduced in the assimilation.
Figure 3. ENSO precipitation index (a), and recent inter-annual anomalies in (b) the MODIS normalized fire-count, and (c) MOPITT 700 hPA CO mixing ratio ( ppbv ) for individual SH regions
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