Yutaka Kondo
email: kondo@atmos.rcast.u-tokyo.ac.jp
Research Center for Advanced Science and Technology
University of Tokyo
4-6-1 Komaba, Meguro
Tokyo 153-8904
JAPAN

Young J. Kim
email: yjkim@kjist.ac.kr
Advanced Environment Monitoring Research Center
Kwangju Institute of Science and Technology
1 Oryong-dong
Gwangju 500-712
KOREA

Aerosols and oxidants are important atmospheric components both due to their impact on air quality and because they are radiatively important, affecting climate on a regional and sometimes global scale. Mega-cities are significant sources for aerosols and oxidants, so it is critical that we understand the key chemical and physical processes controlling the concentrations of these species in these regions.

To date, most large-scale, coordinated measurements of aerosols and oxidants (such as those made under the IGAC Aerosol Characterization Experiment, or "ACE", campaigns; c.f. Quinn and Bates article in IGACtivities No. 28) have taken place in regions well downwind of sources. Such campaigns have allowed us to characterize aerosols and oxidants after they have evolved in the atmosphere for one or more days. While this information is useful for understanding the large-scale impact of pollutants on a region, there are two weaknesses to this approach: 1) The airmasses measured during these campaigns have often mixed with natural background gases and aerosols (such as dust, sea salt, biogenic organics, and biogenic SO₄^2-) or are composed of pollutants from several regions, making it difficult to determine the anthropogenic fraction of what is being measured, and 2) Important chemical transformations occur rapidly after emission. It is only by making measurements near the sources that we will be able to make the link between source emissions and regional-scale air quality and climate impacts. Further, an increased understanding of aerosol and organic chemistry in mega-city regions would lead to more accurate numerical model predictions of future changes in air quality and radiative forcing in urban centers and surrounding regions.

Here we describe an IGAC Task, Mega-Cities:Asia, which will study the concentrations and chemical characteristics of aerosols and organics in a series of Asian mega-city clusters. We hope that this is the first in a series of IGAC Tasks that will study the many mega-city clusters around the globe that have a significant impact on air quality and climate and that Mega-Cities:Asia can be a model for the formation of the other Mega-city Tasks. As a start to this process, one of the sessions at the 2004 IGAC Conference in Christchurch, New Zealand will be "Mega-cities". We look forward to sharing ideas and results with other researchers working on this problem and hope to use this session to initiate collaborations.

The main objective of the Mega-cities:Asia Task is to investigate the contribution of pollutant emissions from mega-cities to local and regional (including Asian Pacific) air quality and to the radiation budget. Investigation of trends in emissions is also of interest. These data will be used to improve models' ability to reproduce current distributions of aerosols (inorganic aerosol, organic aerosol, and black carbon) and oxidants in Asian mega-cities and to improve their accuracy in predicting future changes in air quality. These will be achieved by:

• Characterizing the temporal and spatial changes of aerosols, oxidants, and their precursors, primarily by surface measurements near urban centers and their downwind (Figure 1). Temporal variations to be determined include diurnal variation; variations as-sociated with synoptic scale disturbances; and seasonal variation.
• Characterizing the composition, mixing state, and physical properties of aerosols in urban air. This includes determining the hygroscopic and radiative properties of urban aerosol. This information is important for understanding the impact of aerosols on the radiation budget.
• Validation of emission inventories of trace gases (e.g., NOx, SO₂, NH₃, and VOCs) through comparisons of ratios of concentrations of trace species observed in urban air.

This task is focused on the direct impacts of human activities on the atmosphere in Asian mega-cities and their surroundings. The influence of human activities should change depending on natural conditions, including meteorological conditions, humidity, and solar radiation. These relationships will be investigated by studying seasonal variations of pollutants and the associated meteorological conditions.

We note that this task is closely related with the Atmospheric Brown Cloud (ABC) project that is currently being planned as a follow-on to the 1999 Indian Ocean Experiement (INDOEX) campaign. ABC will concentrate on regional effects on locations downwind of large sources. The Mega-cites Asia Task will be helpful to the ABC study in providing more detailed information on atmospheric composition in the source regions.

The first step to achieving these scientific objectives is the establishment of a network of measurements in Asian mega-cities and their surroundings. To this end, the Mega-cities:Asia Task team will:

1. Generate a database of the measurements of aerosols, ozone, and their precursors that are currently being made (location, investigators, measurement methods, period, etc.) and post them on a centralized web site at the University of Tokyo. If there is a need, we will also post them on other web sites.
2. Encourage the various investigators to employ a uniform set of measurement techniques in an effort to obtain comparable data sets of high quality.
3. Inter-compare common measurements being made in different cities. Where possible directly compare instruments, using a single instrument as a “transfer standard” that is taken to each mega-city for comparison on-site.
4. Develop an implementation plan for how the various data sets from the Asian mega-cities could be combined and analyzed to deduce regional impacts.
5. Establish an explicit plan for data archiving and a protocol for making data public.

We have identified six Mega-cities or City Clusters that could be studied under this Task:

• Japan: Tokyo
• South China: Hong Kong-Guangzhou-Macau cluster
• Taiwan: Taipei
• Korea: Gwangju and Seoul
• East China: Shanghai-Nanjing-Hangzhou cluster
• North China: Beijing-Tianjin-Hebei cluster

Details of the four planned or existing studies are given below:

a) IMPACT: Integrated Measurement Program for Aerosol and oxidant Chemistry in Tokyo
Observational Site:
Research Center for Advanced Science and Technology, University of Tokyo
Observational Periods:
Starting in April 2003
Parameters observed:
Meteorological parameters: Temperature, winds, humidity
Radiation:
J(O¹D), J(NO₂), (spectroscopic actinic flux measurements)
Gases:
NO, NO₂, NOy (chemiluminescence), HNO₃ (CIMS), PAN (in preparation), NMHCs, GC-FID, Oxy-Organics (PTR-MS), O₃ (UV absorption), CO (IR gas correlation), SO₂, (UV fluorescence), CO₂ (NDIR), NH₃(in preparation)
Aerosols:
Chemical composition (aerosol mass spectrometer, ion chromatography), organic aerosols (thermal-optical method), mass loading of PM 1.0 (TEOM), size distribution (DMA).

b) Integrated Measurement Program for Aerosols and Oxidants in Pearl River Delta (Hong Kong-Guangzhou-Macau cluster)
Observational site:
A number of sites in Pearl River Delta, including Guangzhou city and rural areas
Observational periods:
Starting in 2004, with pilot measurement starting in October, 2003
Parameters observed:
Meteorological parameters:
temperature, winds, humidity, radiation, light scattering
Gases:
NO, NO₂, NOy (chemiluminescence), HNO₃ (SJAC), VOCs (GC-FID), O₃ (UV absorption), CO (IR gas correlation), SO₂ (UV fluorescence), NH₃ (SJAC), H₂O₂ (in preparation), OH (in preparation)
Aerosols:
ion chemical composition (ion chromatography), elements (ICP), OC/EC (Sunset), organic aerosols speciation (GC/MS), mass loading of PM 2.5 (TEOM), size distribution (MOUDI)

c) Aerosol studies in Taipei, Taiwan
Chemical and physical properties of aerosols have been made once per month since March, 2000 at four sites around Taipei. One is at Yangming Mountain, which is a remote mountain site (~1 km above sea level) north of Taipei. Measurements are also made continuously at two sites in the Taipei metropolitan area. The fourth site, Shi-men, is at the northern tip of Taiwan. This is on the windward side of the Asian winter monsoon, making it ideal for assessing the impact of long-range transport. All four sites are located at or near the Taiwan EPA’s air quality monitoring stations, which can provide routine measurements of key air pollutants as well as meteorological parameters. Specific instruments at each site are listed below:
Yangming Mountain
Parameters observed:
Aerosols:
Chemical composition: Ions (Ion chromatography), elements (ICP/XRF), OC/EC (Thermal Optical Reflection), mass loading of PM 2.5 (Andersen Dichotomous sampler), mass loading of PM 10 (Andersen Dichotomous sampler)
Taipei Metropolitan sites
Parameters observed:
Aerosols:
chemical composition: sulfate (R&P 8400S), nitrate (R&P 8400N), OC/EC (R&P5400), black carbon (Magee Scientific AE-31 Aethalometer), total PAHs (EcoChem PAS 2000), mass loading of PM 2.5 (R&P 1400a), size distribution (SMPS 3936L22), size distribution (PMS PCASP-X), light-scattering coefficient (TSI 3563)
Shi-men site
Parameters observed:
Aerosols:
chemical composition: ions (ion chromatography), elements (ICP/XRF), OC/EC (Thermal Optical Reflectance), mass loading of PM 2.5 (R&P 2300), mass loading of PM 10 (R&P 2300 and TEOM), size distribution (MOUDI), size distribution (PMS PCASP-X), light-scattering coefficient (TSI 3563 nephelometer).

d) Aerosol studies in Korea
Possible Mega-cities or City Clusters to be studied:
Gwangju and Seoul, Korea
Period:
2003-2006 Gwangju Site (K-JIST/ADEMRC)
Parameters observed:
Aerosols:
Aerosol vertical profile (Multi-channel LIDAR), size distribution (MOUDI, aerosol profiler), ions (ion chromatography), elements (ICP/XRF), OC/EC (Thermal Optical Reflection carbon analyzer), mass loading of PM (WINS sampler, URG PM10 & PM2.5 samplers, Dichotomous sampler)
Radiation:
CIMEL Sunphotometer, MFR-7, UV-MFR-7, UV-A, UV-B
Optical measurement:
LP-DOAS (SO2, O₃, NO₂, HONO, HCHO, BTEX), light extinction (Transmissometer), light scattering (nephelometer), light absorption (aethalometer)
Seoul Site
Parameters observed:
Aerosols:
size distribution (MOUDI), ions (ion chromatography), elements (ICP/XRF), OC/EC (Thermal Optical Reflection carbon analyzer), mass loading of PM (URG PM10 & PM2.5 samplers, Dichotomous Sampler)
Optical measurements:
LP-DOAS (SO₂, O₃, NO₂, HONO, HCHO, BTEX), light extinction (Transmissometer), light scattering (nephelometer), light absorption (aethalometer)

The IMPACT and Pearl River Delta measurements are underway and are expected to continue into 2005. Measurements in Taiwan are ongoing on a nearly continuous basis. The Mega-city Task team will coordinate joint intensive campaigns in order to characterize the regional impact of emissions from each mega-city. Because these campaigns are not fully concurrent and because they are currently being conducted independent of one another, the Mega-city Task team will host a data workshop each year that will bring these groups together. This will help ensure that measurements continue to be made in as uniform a manner as possible and will facilitate collaboration between researchers working in different mega-cities. Each study group will of course publish results as part of their individual campaigns. The Task team will make sure that, in addition, studies that integrate the various data sets will also be published.

Key to the integration of these data sets will be not only the uniformity of the measurements but also a careful assessment of the uncertainties in the meas-urement of key species:
Organic aerosol and black carbon - No international standard measurement techniques exist for measuring OC and EC. Thus, the University of Tokyo group will do a comparison of the different techniques being used and will transfer this knowledge to the participating groups. This effort is scheduled to commence in 2005.
NOx, NOy and CO – It is most important that the measurement of these two key species be carefully calibrated. There are several ways that accuracies might be improved: 1) assurance of the calibration gas; 2) proper zeroing; 3) a careful check of the con-version efficiency for NOy.

The activities discussed above constitute the first phase of what we hope will be a multi-stage Mega-cities:Asia Task. These activities were chosen because they are achievable in a reasonable time-frame (i.e. ~3 years) and because they lay the necessary groundwork for producing the unified data set needed to analyze the impact of Mega-cities on a regional or global scale.

The data utilized under the Mega-cities: Asia Task will be archived and will be open to participants. A uniform dat archiving plan will be generated by the Task Steering Committee. Data will be made available to public three years after the data were taken.

The Task Team plans to have young visiting scientists for each Mega-city experiment and will take advantage of the intercomparison and calibration workshops to engage young researchers. This will give opportunities for young scientists to learn about the differences and similarities in the atmospheric environment of different cities.

The Team also plans to have a modelling summer school. Megacity activities on training might also be coordinated with the WMO Urban Meteorology and Environment Research Project (GURME). This project is focused on air quality forecasting and one of its tasks is to run regional training workshops.

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