Japan & S. Korea India China

North America

Europe

S. Hemisphere

1.00.80.60.40.20.0

Asian Mega Cities

AOT measurements from MODIS onboard Terra and Aqua satellite provide an accurate and cost effective way to monitor air quality areas where ground based observations are not available. Satellites observations suggest that pollution level is high in mega cities of developing counties and lower in developed countries particularly in the southern hemisphere. In the present study the Air Quality Index is calculated for each city based on the EPA (USA) standard which could differ depending on the air quality standard of each country.

Pawan Gupta1, Jun Wang1, Sundar A Christopher1, Jenny Hand2

1Department of Atmospheric Science, University of Alabama in Huntsville, Huntsville, AL; 2Co-operative Institute for Research in the Atmosphere (CIRA), Colorado State University, Fort Collins, CO

Introduction

The concentration of particular matter with aerodynamic diameter less than 2.5µm (PM2.5) is an important parameter that has been taken by many countries to evaluate the air quality. In recent years, research studies have shown the potential of monitoring air quality from space based observations, a possibly cost-effective method for regions where the ground-based PM2.5 measurements are sparse. Using MODIS columnar aerosol optical thickness (AOT) product from Terra and Aqua satellites together with ground-based observations, this study evaluates the advantages and disadvantages of this method.

Methodology

Ground-based hourly measurements of PM2.5 are compared with collocated MODIS AOT for one year over several megacities in the world, and rural areas in United States. Human population data is also used to evaluate the anthropogenic effects on air pollutions.

Data Used

1) MODIS level 2 and 3 AOT and AOT Fine Mode Fraction from both Terra and Aqua for 2002.

2) Hourly ground observation of PM2.53) Human population data set in 1 degree grid resolution, 19904) Monthly-averaged PM2.5 data from IMPROVE measurements in 2001 and

2002.

Case Studies of MODIS AOT vs. PM2.5

Inter-comparison performed over Alabama, Texas, New York, Switzerland, Hong Kong, New Delhi and Sydney show that satellite measured AOT are well correlated with ground based measurements of PM2.5 and could be an important tool to monitor the air quality in remote areas where ground based stations are not available.

Spring Summer

Fall Winter

Population vs AOT

Regional Variations in Population and AOT

Relationship between human population and aerosol loading is explored. Box averaged AOT and population shows similar variations from one region to other region, indicating that MODIS Fine Mode fraction shows good correlation with population.

Summary

1) Satellite derived aerosol optical depth and ground based PM2.5 mass are compared over selected regions of the world.

2) MODIS AOT has a good positive correlation (around 0.7) with PM2.5 mass concentration, and this linear coefficient varies in different parts of the world. In United States, among comparisons between MODIS AOT (small fraction) vs. IMPROVE PM2.5 at 144 stations (most are in rural area), about 25% show the negative relation, mainly in the southwest coast and high latitude regions, and 30% show correlation larger than 0.7., mainly in eastern and middle latitude regions. Overall, the MODIS AOT can be used to assess the air quality categories such as good, moderate, unhealthy to relatively high degree of confidence.

3) Assessment of air quality in 100 mega cites using MODIS AOT shows that cities in developing countries are more polluted compared to cities in developed countries.

4) MODIS AOT fine mode fraction could be a good indicator of pollution produced by human activity in different megacities.

ReferencesWang J., and S. A. Christopher, Intercomparison between satellite derived aerosol optical thickness

and PM2.5 mass: Implications for air quality studies, 30(21), 2095, 2003.Christopher et al., Pollution in mega cities from satellite measurements, in preparation.

AcknowledgementThis research was supported by NASA’s Radiation Sciences, Interdisciplinary sciences and ACMAP

programs. J. Wang is supported by the NASA Earth System Science Graduate Fellowship

Satellite Observation of Air Quality in Megacities Global Distribution of Population and Pollution

MODIS AOT vs. IMPROVE PM2.5 in U.S.

Monthly-mean IMPROVE PM2.5 data are merged into grid data with grid size of 1X1 degree, and compared with MODIS level 3 AOT data (1X1 degree, small fraction).

The annual mean of MODIS AOT (small fraction) and PM2.5 shows similar distribution pattern, with high aerosol concentration the eastern U.S. and low concentration in western U.S. (except in California).

PM2.5 vs AOT in Switzerland PM2.5 vs AOT in NewYork City PM2.5 vs AOT in Sydney

Time

PM2.

5

MO

DIS

AO

T

PM2.5 vs AOT in Texas (USA) PM2.5 vs AOT in Hong Kong 24 hr Mean PM2.5 vs AOT

PM2.5 (µgm-3) PM2.5 (µgm-3)

MODIS AOT IMPROVE PM2.5Correlation

Annul Mean in 2002 Annul Mean in 2002 Monthly MODIS AOT vs. PM2.5

Correlation Histogram

Global Population Distribution, 1990

MODIS Fractional Fine Mode, 2002

1 2

3

4 910

56

7

8

11

12

Email: wangjun@nsstc.uah.edu; URL: http://www.nsstc.uah.edu/~wangjun

AGU 2004, A11A-0034

AGU 2004 Air Quality in Megacities Session