2.1 Scientific Issues

The primary motivation for TRACE-P is the rapid industrialization presently taking place in Asia. Energy use, principally fossil fuel combustion, in eastern Asia has increased substantially over the past decade and it, NOx, and other pollutants, are expected to continue to increase as development proceeds. This presents a unique opportunity to observe the time-dependent atmospheric impact of what is essentially an ongoing major industrial revolution. Long-term observations from ground sites and satellites can provide continuous monitoring of the temporal trend of atmospheric composition but are limited in spatial coverage (in the case of ground sites) or in the suite of species measurable (in the case of satellites). Focused aircraft missions complement surface and satellite observations by providing detailed investigations of the dynamical and chemical processes affecting atmospheric composition over rather broad geographical regions.

The March-April flight period for TRACE-P was selected after consideration of several factors [Jacob et al., 1999].  Spring is the season of maximum Asian outflow over the north Pacific, due to a combination of active convection over the continent and the presence of persistently strong westerlies. In summer, deep convection often exports Asian air to the upper troposphere above 12 km, while outflow at lower altitudes in that season is deflected to polar latitudes by the circulation around the Pacific High. In winter, a significant fraction of the Asian outflow may head south rather than east. Spring affords the best opportunity to not only sample Asian outflow, but also the emissions associated with biomass burning from the northern tropics (as indicated by a March-May maximum in tropospheric ozone measured over Hong Kong). Long-range transport of Asian dust over the north Pacific is also at a maximum in spring. Photochemistry over the western Pacific is active from February to March, and intensifies with the advance of the spring season.

2.2 Previous Related Missions

The GTE PEM-West A and B missions examined the impact of natural and human activities on the chemistry of the troposphere over the northwestern Pacific Ocean from 10˚N to 50˚N. PEM-West A was conducted in August-September 1991 and PEM-West B in February-March 1994. Important meteorological differences between these two seasons include the position and strength of the Japan Jet, and the location of the Pacific High [Merrill et al., 1997]. During August-September (PEM-West A), the Japan Jet is weaker and shifted north compared to February-March (PEM-West B). The Pacific High is at its northernmost and easternmost position during August-September, impeding continental outflow and enhancing inflow of marine air to the western Pacific from the south particularly at low altitudes. In PEM-West A, this southerly flow was accompanied by extensive vertical mixing along a typhoon storm track oriented parallel to the Asian coast; continental outflow was largely confined to north of 40˚N. PEM-West B experienced stronger and faster continental outflow over an extended range of latitudes, principally below 5 km due to weak convection over eastern Asia in winter. Blake et al. [1997] found higher mixing ratios of continental hydrocarbons and halocarbons during PEM-West B than A, especially at low altitudes, and similar observations were made for acidic gases [Talbot et al., 1997]. The composition of the hydrocarbon mix indicated a more recent origin for the continental outflow in PEM-West B.

The strong Asian outflow during PEM-West B had a major influence on the regional ozone budget over the western Pacific. Photochemical model calculations by Crawford et al. [1997] showed net ozone production taking place at all altitudes, in contrast to PEM-West A where net loss at low altitudes balanced net production at higher altitudes. PEM-West B marked the first time that net ozone production has been found to take place in the lower marine troposphere. That this condition was observed in late winter/early spring further emphasizes the critical role of fast transport of ozone precursors from the Asian continent. Calculated rates of increase in the tropospheric ozone column during PEM-West B were as large as 2% per day south of 30N and 1% per day to the north. An important implication of the rapid transport observed during PEM-West B is that the photochemical activity of the continental outflow remained strong even after several days of travel time over the ocean.

The initial findings were published in the Journal of Geophysical Research-Atmospheres in January 1996 (PEM-West A) and in December 1997 (PEM-West B). The data can be accessed directly from the GTE ftp site (https://www-air.larc.nasa.gov/pub/) or through the GTE Web Site (http://www-gte.larc.nasa.gov) using the "Data Archive" hot link. Data can also be accessed from the Langley DAAC Web Site (http://eosweb.larc.nasa.gov) through the "Access Data" then "Data Accessible from the Web" hot links. The GTE ftp and GTE web sites provide data files for individual investigations, on a flight-by-flight basis, while the DAAC site provides a single file of all the data from all investigators, on a flight-by-flight basis. Data from ozonesonde launches during PEM-West B are also available on the GTE ftp site.

2.3 Concurrent Missions

TRACE-P will be collaborating with the following concurrent missions.  Specific details of these collaborations are given in the formal signed agreements, which are included in Appendix M.

2.3.1 ACE-Asia

The Aerosol Chemistry Experiment – Asia (ACE-Asia) campaign will take place in early spring, 2001. The overall goal of ACE-Asia is to reduce the uncertainty in climate forcing caused by aerosols over Eastern Asia and the Northwest Pacific and to develop a quantitative understanding of the multi-phase gas/aerosol particle/cloud system. To achieve this goal, the ACE-Asia Program as a whole will pursue three specific objectives. The first objective is to determine the physical, chemical, and radiative properties of the major aerosol types in the Eastern Asia and Northwest Pacific region and investigate the relationships among these properties. The second is to quantify the physical and chemical processes controlling the evolution of the major aerosol types and in particular of their physical, chemical, and radiative properties. The last objective is to develop procedures to extrapolate aerosol properties and processes from local to regional and global scales, and assess the regional direct and indirect radiative forcing by aerosols in the Eastern Asia and Northwest Pacific region. There is the possibility of several joint aircraft flights with TRACE-P and data exchange is planned.



The Biomass Burning and Lightning Experiment (BIBLE) Phase C is scheduled to conduct measurements in the Western Pacific during December 2000 which will provide data supplemental to the TRACE-P mission.  The Japanese Earth Observation Research Center (EORC), National Space Development Agency of Japan (NASDA), will conduct BIBLE. The goal of BIBLE is to study tropospheric chemistry (natural and anthropogenic processes) in the tropical Asia/Pacific region.  Measurements of ozone, ozone precursors and other photochemical quantities will be made aboard a Gulfstream II aircraft.  In addition, BIBLE Phase C will be making measurements of lightning over the Western Pacific during the ferry flights to and from Northern Australia and Indonesia. The Pacific Exploration of Asian Continental Emission (PEACE) mission, also conducted by EORC/NASDA, will take place in January 2002 and will also provide data supplemental to TRACE-P.  Using the Gulfstream-II aircraft mentioned above, PEACE will make measurements of the seasonal excursion of the continental outflow from Asia.  Data exchange is planned.  

2.3.3 MOPITT

The exchange of data between TRACE-P and MOPITT (aboard the TERRA satellite) will benefit both parties by making MOPITT data available to TRACE-P for mission planning and TRACE-P data available to MOPITT for mission validation purposes.  TRACE-P requests the MOPITT level 2 CO daily maps for the TRACE-P mission area.   This data will be used for mission planning only.  In turn, NASA will make TRACE-P available early to MOPITT staff for instrument validation purposes.  Any other use of the TRACE-P data will conform to the constraints of the TRACE-P Data Protocol (see Section 6.1).

2.3.4 NAST

The National Polar-orbiting Operational Environmental Satellite System (NPOESS) Aircraft Sounder Testbed (NAST) is a technology demonstration instrument flown on high altitude aircraft and developed to reduce risk associated with future NPOESS satellite instruments whose purpose will be to improve operational weather forecasts.   TRACE-P and the NAST Asian Pacific experiment will derive mutual benefit from having a cooperative agreement between the two Science Teams.  Per the agreement, the two Science Teams will share flight planning products during the mission expeditions when possible, to design coordinated joint flights, and to share post-mission data.  Field data may be freely shared between the two Science Teams for designing and evaluating joint flights during the execution of the missions.  These data are not to be used for publication.  The TRACE-P and NAST data may be shared prior to public release provided that the TRACE-P and NAST investigator(s) have agreed to abide by each other’s data protocols.

2.3.5 University of Washington

The University of Washington and Dr. Daniel Jaffe, Professor, are planning 8-10 profiles from a small aircraft (Beechcraft Duchess) platform during the spring 2001, coinciding with the TRACE-P/ACE-Asia time period.  Flights will be timed to optimize the likelihood of observing trans-Pacific transport of pollutants as well as identify air masses, which were sampled, by one of the TRACE-P aircraft.  Flight decisions will be made using all available meteorological, chemical forecast, and satellite data.  The profiles will be conducted just off the coast Washington state, under a generally western regime to at least 20,000 feet.  Aircraft measurements will include in situ ozone, in situ sub-micron aerosol scattering coefficient, and CO and NMHCs in canisters (8-10 per flight).  In addition, Dr. Jaffe will be making ground-based observations at Cheeka Peak.  These observations include CO, O3, NOy, NMHCs, aerosol scatter, and aerosol chemical composition.  Data exchange between TRACE-P and the University of Washington is planned and will conform to the constraints of the TRACE-P Data Protocol (see Section 6.1). 

2.4 Other Collaborative Efforts

This section lists other collaborative efforts, which will contribute to the TRACE-P mission.  Additional details are provided in the formal, signed agreements with the following agencies (see Appendix M).

2.4.1 ECMWF

 The European Center for Medium-Range Weather Forecasts will provide meteorological products to TRACE-P (through MIT) from January 9, 2001 to April 12, 2001.  Products that will be provided include forecast data on model levels (60).  The forecast data includes U and V wind components, vertical velocity, temperature, specific humidity, ozone mass mixing ratio, and Ln surface pressure (single level). Forecasts are from 12 UTC with time steps of T+12, +24, +36, +48, +60, and +72.  Analysis data on model levels (60) include the forecast data products listed above as well as orography (single level) at 00 and 12 UTC.  Analysis of surface data will also be provided at 00 and 12 UTC.  Surface data products include surface pressure, soil temperature, 10 meter U and V wind components, 2 meter temperature and dew point, mean sea level, orography, land/sea mask, surface sensible heat flux, surface latent heat flux, surface solar radiation, top solar radiations, top thermal radiation, east/west surface stress, north/south surface stress, and total cloud cover.  TRACE-P will provide lidar-based ozone profiles in exchange.

2.4.2 Hong Kong Observatory

Hong Kong Observatory (HKO) and TRACE-P will both benefit from collaboration related to the TRACE-P mission.  NASA ‘s responsibilities include: providing balloon-borne ozonesondes and balloons at no charge to HKO as required to meet the enhanced launch schedule, provide HKO with access to the TRACE-P mission data as requested by HKO and following the data protocol established by the TRACE-P Science Team, invite HKO investigators to attend post-campaign data workshops, and allow HKO access to data obtained by TRACE-P Principal Investigators.  In turn, HKO will use reasonable efforts to do the following:  launch ozonesondes at a rate of one per week beginning at the completion of this agreement until May 2002 and at a rate of two per week during the six weeks of the TRACE-P mission; provide balloon inflation gases; record the resulting data in NASA designated format and make the database accessible to the world in a timely manner; provide copies of the resulting data to NASA as soon as possible, but not later than three months after each launch; and participate in post-campaign data workshops.

2.4.3 Hong Kong Polytechnic University

Hong Kong Polytechnic University and Dr. Tao Wang will carry out measurements over a two-month period coinciding with the TRACE-P mission at the HKPU atmospheric research station at Hok Tsui and make the data available to the TRACE-P Science Team.  Measurements taken will include ozone (surface and column), CO, NO, NOy, SO2, radon, NMHCs, halons, and C1-C2 alkyl nitrate (canister samples collected at a rate of 1-4 per day during the TRACE-P flight), aerosols (mass concentration and full chemical composition at a rate of 1-2 per day during the flight period), and auxiliary meteorological measurements (UV-B, wind direction and speed, temperature, and relative humidity).  NASA will make all of the TRACE-P data available to HKPU within the constraints of the TRACE-P Data Protocol (see Section 6.1)

Dr. Tao Wang is invited to participate in TRACE-P data workshops, Science team meetings in Hong Kong.  The possibility of Dr. Tao Wang flying aboard a NASA aircraft during the mission is being explored.

2.4.4 Japan Meteorological Agency

 NASA requests the following from the Atmospheric Environment Division of the Japan Meteorological Agency (JMA):  data at all levels from the JMA ozonesonde stations at Sapporo, Tsukuba, Naha (Okinawa), and Kagoshima beginning as soon as possible through October 2001; a digital copy of the ozonesonde and total ozone data from the four stations for approximately the past 10 years; CO2, CH4, CO, and surface ozone data from the JMA Greenhouse Gas stations at Ryori, Yonagunijima, and Minamitorishima a few months after the early April 2001 completion of TRACE-P; and the GMS image data discussed during Professor Reginald Newell’s visit to Dr. Uchino in June 2000.  NASA will make all TRACE-P data available to JMA within the constraints of the TRACE-P Data Protocol (see Section 6.1).  All TRACE-P publications using JMA provided data would clearly note the data source.

2.4.5 NASA GSFC Data Assimilation Office

The Data Assimilation Office’s (DAO) mission is to advance the state of the art data assimilation and to produce research-quality global data set for advancing our understanding of the Earth system and global change.  To this end, DAO has been providing Data Assimilation System (DAS) data products in support of Earth science mission activities.  The responsibilities of DAO are as follows: produce DAS meteorological analysis and forecast products every 12 hours during the TRACE-P mission (February 25 to April 10, 2001), design and implement all necessary software to generate in HDF-EOS format the reduced DAS data set for chemical tracer forecasts, provide the reduced data set for the network transmission to the TRACE-P mission in accordance with NASA AMES/NAS security policy, and generate the above analysis and forecast data for a limited period in the fall 2000 as a “dry run”.

GTE’s responsibilities in turn include: transfer the DAS data set from the DAS site using an agreed upon transfer mechanism that meets security requirements at AMES/NAS, generate chemical tracer forecasts during TRACE-P using DAS products, generate chemical tracer forecasts for the “dry run”, restrict access to DAS products to the members of the TRACE-P Science Team, and provide DAO with feedback on the scientific quality of the DAS data products.

2.4.6 National Taiwan University, Central Weather Bureau of Taiwan

As part of the APARE, National Taiwan University (NTU) and the Central Weather Bureau of Taiwan launch two ozonesondes per month.  NASA requests that this launch frequency be increased to one per week from March 2000 to March 2002 and two launches per week during TRACE-P (March 1 – April 9, 2001).  In turn NASA (or NOAA on NASA’s behalf) will provide the additional ozonesonde systems required to meet this enhanced frequency.  NTU and/or the Central Weather Bureau will provide the balloon inflation gases and the resources to launch the ozonesondes, record the data, and provide copies of the data to NASA as soon as possible after each launch, but no later than 3 months after the launch.  TRACE-P mission data will be made available within the constraints of the data protocol (see Section 6.1).



TRACE-P will build on the heritage of the previous GTE PEM-West missions. The PEM-West missions were exploratory, with multiple objectives achieved from a single aircraft. TRACE-P will provide a considerably more extensive characterization of the Asian outflow to allow for quantitative interpretation. In addition, TRACE-P will take advantage of numerous developments in aircraft instrumentation over the past decade including in particular measurements of HOx, NOx, sulfur, species, aerosols, and UV actinic fluxes. Ten years will have elapsed between PEM-West A and TRACE-P, during which Asian emissions will have grown considerably (70% for NOx; van Aardenne et al. [1999]). Secular change in the composition of the Asian outflow should be apparent between the PEM-West and TRACE-P missions.

TRACE-P will continue investigation of tropospheric chemistry in the western Pacific. It will be an airborne study that will complement the PEM-West missions. It will be conducted during early spring, 2000, thereby providing an opportunity to investigate the changes in the Asian influence in the western Pacific. The study region will range from 110˚E to 150˚E longitudes with major deployment sites in Hong Kong and Japan. The NASA DC-8 and P-3B aircraft will be the primary measurement platforms.

Integration of aircraft, satellite, and ground-based studies will be a defining characteristic of TRACE-P. This synthesis will be possible because of the availability of both important new satellite data in 2001 and complimentary data from APARE, which will include a number of other airborne and ground-based measurements. TRACE-P will also require a very strong coupling between experimental investigations and modeling studies. The modeling studies will provide critical tools for detailed flight planning, in-field, quick-look data analysis and for post-mission data analyses. Taken together, the full suite of measurements and modeling investigations will enable the TRACE-P team to reach the major objectives, especially when combined with large-scale models capable of integrating the ground-based, aircraft-based, and satellite-borne data. The nominal transit flight tracks for the DC-8 and P-3B aircraft during TRACE-P are shown in Figure 2.5-1.  Figure 2.5-2 shows the local flights based out of the intensive sites. 


Figure 2.5-1 TRACE-P Nominal Aircraft Transit Flight Tracks

TP Transit Map




Figure 2.5-2 TRACE-P Nominal Aircraft Local Flight Tracks

TP Local Map


2.5.1 General Objectives

Reflecting our current state-of-knowledge of Asian outflow and the western Pacific, two strongly focused scientific objectives are defined for TRACE-P:


The first objective of TRACE-P is to identify the major pathways for Asian outflow over the western Pacific, and to chemically characterize the outflow in a way that provides a basis for quantitative model analysis of export from the Asian continent. A number of 3-D chemical tracer models have been used in recent years to examine Asian influence on global atmospheric composition (see references in the TRACE-P white paper). TRACE-P will provide the information needed to test these models. We expect the Asian chemical outflow over the western Pacific to represent a complicated superposition of contributions from different Asian source regions and from long-range transport of European and North American pollution. The Asian emissions themselves represent a mix of contributions from fossil fuel combustion, other industrial activities, biomass burning, vegetation sources, and soil dust. Scavenging of soluble aerosols and gases during wet convective transport out of the boundary layer modifies the composition of the outflow, and unusually strong stratosphere-troposphere exchange around the Japanese jet further complicates the interpretation of the outflow. The use of two aircraft in TRACE-P will allow the sampling of a range of Asian outflow pathways in different regions and at different altitudes, as is needed to support quantitative analyses of export from the Asian continent.


The second major objective of TRACE-P is to better understand the chemical evolution of the Asian outflow over the west Pacific, focusing on tropospheric O3 and aerosols. The processes involved in this evolution include photochemistry, heterogeneous chemistry, gas-to-particle conversion, aerosol growth, scavenging, and subsidence to the marine boundary layer followed by rapid removal of some species by deposition. Different patterns of evolution are expected depending on the direction of outflow (tropics vs. high latitudes); the altitude (boundary layer vs. free troposphere); the presence of soil dust, soot, or other chemically active aerosols in the outflow; and the contributions from natural sources including lightning and stratospheric intrusions. Previous studies (see references in the TRACE-P white paper) have pointed out that strong UV radiation and heterogeneous chemistry involving dust aerosols may play an important role in modifying the chemical composition of the Asian outflow over the western Pacific. A strong integration of TRACE-P aircraft and ground-based data, with data from satellites, and data from other APARE projects, such as ACE-Asia, will be essential to enable the analytical studies needed to address this objective.

2.5.2 Specific Tasks

Within the framework of these general objectives, five specific tasks are identified:

1. To identify and quantify the contributions to Asian outflow from industrial sources in Asia, Europe, and North America, as well as from biomass burning sources in Southeast Asia and northern Africa.

2. To demonstrate the potential for synergistic integration of aircraft and satellite observations, together with three-dimensional models, to quantify the chemical outflow from a major continental source region.

3. To determine the importance of natural processes (lightening, stratospheric down welling) contributing to the Asian outflow.

4. To understand the long-range transport and chemical aging of Asian pollution over the North Pacific, and to assess the implications for global influence and for intercontinental transport of pollutants.

5. To determine the role of heterogeneous chemistry in controlling the chemical evolution of the Asian outflow over the Pacific.


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