Chemical Remote Sensing
David Edwards (Group Leader)
ACRESP activities build on our current satellite missions and our expertise and leadership in satellite remote sensing science, Earth System modeling, and data assimilation. Recent advances in tropospheric remote sensing have opened the way for measuring, monitoring, and understanding processes that lead to atmospheric pollution. As part of an integrated observing strategy, satellite measurements provide a context for localized observations and help to extend these observations to continental and global scales. The challenge for future space-borne missions will be directly accessing the local scale and facilitating the use of remotely sensed information for improving local- and regional-scale air quality (AQ) forecasts. Achieving this goal will provide important societal dividends for public health, for policy applications related to managing national AQ, and for assessing the impact of daily human activity on the distributions of important trace gases and aerosols and their short-timescale variability - known as "chemical weather" - as well as on climate.
Satellite Instrument Design:
If a satellite mission related to atmospheric composition and air quality is to become a reality within the next decade, the atmospheric chemistry community will need to establish clear scientific motivation for the new measurements. For this, there is considerable interest in using chemical observing system simulation experiment (OSSE) studies to help define quantitative measurement requirements for satellite missions and to evaluate the expected performance of proposed observing strategies. These experiments will hopefully provide a practical way of defining a traceability matrix to map science requirements through measurement requirements onto instrument requirements.
OSSEs must be driven by well-defined scientific questions and the experiment formulation constructed accordingly. We have completed an example OSSE motivated by the desire to measure the distribution and time evolution of carbon monoxide in the lower-most troposphere for air quality applications using candidate satellite multispectral measurements in the thermal and near infrared.
Future Satellite Missions:
The ACRESP group is involved in the planning of The Geostationary Coastal and Air Pollution Events (GEO-CAPE) mission that has been recommended for launch in the 2013-2016 time frame by the National Research Council. The mission's purpose is to gather science that identifies human versus natural sources of aerosols and ozone precursors, tracks air pollution transport, and studies the dynamics of coastal ecosystems, river plumes and tidal fronts. Continuous observation from GEO-CAPE's geostationary platform will allow for more adequate monitoring of population exposure and the ability to relate pollutant concentrations to their sources or transport, thereby providing data to improve air quality forecasts.
ACRESP is a partner on a carbon monoxide instrument, the Compact Imaging Spectroradiometer (CISR), that builds on MOPITT experience and that has been specifically designed for geostationary deployment. CISR is candidate technology for GEO-CAPE and is currently under development as part of the NASA Instrument Incubator Program (IIP).
A longer-term goal of the ACRESP OSSE activity is to develop a community facility at NCAR. This would be used by researchers from the universities and agency centers for building and testing instrument simulators as part of the proposal and design of the next generation of satellite instruments.
Air Quality "Chemical Weather" Forecasting:
The Chemical Weather: Local, regional, and global distributions of important trace gases and aerosols and their variation on time scales of minutes to hours to days, particularly in light of their various impacts, such as on human health, ecosystems, the meteorological weather, and climate. (Lawrence et al., Environ. Chem. 2005, 2, 6-8, doi:10.1071/EN05014)
The ACRESP Program is developing an air quality "chemical weather" forecasting capability based on existing satellite observations. Chemical weather is a priority research theme for ESSL. The characterization of global and regional scale air quality involves field campaigns, chemical transport modeling, and remote sensing. The goal is a scientific and observing framework analogous to that used for weather forecasting with a model assimilation of observations from satellite, aircraft and surface platforms to derive a 4-dimensional view (3 spatial plus temporal) of the physical state of the atmosphere.
This analysis will be used in air quality basic research: the quantification of emissions of ozone and aerosol precursors and the examination of the long-range transport of pollutants extending from regional to global scales. The general tools and methodologies developed will also be used for studies examining the connections between climate change and regional air quality, and the roles of anthropogenic and natural processes in changing atmospheric composition. The predictive capability will provide a powerful tool to support field campaign activities such as those involving HAIPER chemical instrumentation. There also exists the possibility of demonstrating schemes for future operational applications elsewhere in the community related to air quality management and health advisories.
Increasingly, there is interest in accessing finer spatial scales to quantify both the wider impact of local pollution sources such as wildfires and mega-cities and assessing the contribution of transported pollution. We are conducting a chemical weather case study for the MIRAGE and INTEX-B spring 2006 period. This involves global model simulations using analyzed meteorology and the best possible chemical sources with fire emissions based on satellite fire products. A nested regional model simulation concentrating on Mexico and parts of the INTEX-B Pacific region are also being performed using WRF-Chem.
One of the open questions in AQ policy management is to what degree Asian industrialization and the associated transpacific transport of pollution could hinder improvements in AQ in the US from domestic emission controls. We have used the data set collected during the April/May 2006 phase of INTEX-B to look into the impacts of the long-range transport of pollutants across the Pacific on the U.S. West Coast. The study used global model simulations with altered Asian emission scenarios as boundary conditions for WRF-Chem simulations to examine the changes in concentration fields in both the global and the regional model. In another study, we focused on a direct application to AQ and quantified the impact of the fires in California in fall 2007 on regional air quality and especially on surface ozone by analyzing surface observations of ozone concentrations together with model simulations. It was found that the frequency of violations in the public health standards nearly tripled because of the fires.
Assimilation of available satellite data sets such as Terra/Aqua/MODIS aerosol optical depth, ENVISAT/SCIAMACHY and Aura/OMI NO2, OMI O3 tropospheric column, and Terra/MOPITT, Aura/TES, and METOP/IASI CO and O3 are being explored. This exercise will impose constraints on the modeled chemical fields and can be evaluated by compaing with actual field measurements. We have been working on a pre-cursor study with idealized satellite retrievals to examine the benefits and shortcomings in the assimilation of chemically active species. Largest improvements in predicting surface ozone were found when O3 or also NO2 fields throughout the atmosphere are available with high temporal resolution (3hrs) and for the online inversion of NO emission. However, the latter had the tendency for increasing biases in outflow regions. Work is ongoing on the assimilation of concentrations fields on a daily basis.
These projects involve the collaborative efforts between ACD and the DART initiative in IMAGe. We will also aim to foster collaboration with other efforts in the development of chemical weather forecast capability both within U.S. Universities, NOAA and NASA, and internationally, particularly with the GEMS project ( http://www.ecmwf.int/research/EU_projects/GEMS/ ) in Europe.
Field Campaign Support and Data Analysis:
ACRESP supported the NASA Arctic Research of the Composition of the Troposphere from Aircraft and Satellites (ARCTAS) field campaign with a combination of model simulations and satellite observations. Measurements were made from the NASA DC8 aircraft in the Spring and Summer of 2008, and were coordinated with several other field experiments as part of the International Polar Year (IPY). The Spring Phase of ARCTAS was April 1-19, based in Fairbanks, AK, and the Summer Phase was in Cold Lake, Alberta, June 26-July 14. In addition, several DC8 flights were made from Palmdale, CA, June 18-24, in coordination with the California Air Resources Board (CARB).
Retrievals of carbon monoxide (CO) from observations by Terra/MOPITT were produced in near-real-time. Chemical forecasts were produced using Ensemble Kalman Filter Data Assimilation of meteorological observations, MOPITT CO, and MODIS aerosol optical depth (AOD) with the NCAR Community Atmosphere Model with Chemistry (CAM-Chem). The data assimilation was performed in the Data Assimilation Research Testbed (DART) framework. Forecasts were also run with MOZART-4 driven by NCEP/GFS meteorology. The satellite retrievals and chemical forecasts were used to assist in the planning of the DC8 flights during the campaign by identifying features of interest for the aircraft to sample, such as pollution plumes from fires in Siberia and Canada.
Analysis of the ARCTAS measurements will continue in the coming year using a combination of satellite and model simulations. The assimilation of MOPITT CO and MODIS AOD in CAM-Chem/DART will be refined and evaluated with the aircraft observations, and, in turn, used to assist in the interpretation of the observations. Discrepancies between the model and observations will be used to improve the model and the emissions used to drive the model.