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IAAR Seminar 21 May 2013

AOD trends over megacities based on space monitoring using MODIS and MISR

Pinhas Alpert1,2, Olga Shvainshtein1 and Pavel Kishcha1

1Department of Geophysical, Atmospheric and Planetary Sciences2Porter School of Environmental Studies

Tel Aviv UniversityAlpert, P., Alpert, P., Shvainshtein, O., KishchaSS, P. (2012), AOD trends over megacities based on space monitoring using MODIS and MISR. American Journal of Climate Change, accepted.  Climate Change, accepted. 

ted. 

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Alpert, P., Shvainshtein, O., Kishcha, P. (2012), “AOD trends over megacities based on space monitoring using MODIS and MISR “American Journal of Climate Change, 1, 117-131, doi:10.4236/ajcc.2012.13010 Published Online September 2012 (http://www.SciRP.org/journal/ajcc), 2012.

Can also be downloaded from my Publications Website:http://www.tau.ac.il/~pinhas/publications.htm

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The research objectives

To explore the capability of satellite aerosol sensors in

detecting the impact of megacities on the Aerosol Optical

Depth (AOD).

To estimate the effect of urbanization on the AOD over the

largest cities in the world, by analyzing last decade

tendencies of the AOD.

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The sensorsMODIS (Moderate Resolution Imaging Spectroradiometer)

MISR (Multi-angle Imaging

SpectroRadiometer)

Resolution (degrees) 1×1 0.5×0.5

Global coverage time

Every 1-2 days Every 9 days

Equator crossing: Terra10.30 a.m. –

local time (north to south)

Aqua13.30 a.m. – local time

(south to north )

10.30 a.m. – local time (north to south)

View angles 1 angle 9 different angles

MISR

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Methodology and data

The 189 largest cities in the world with population exceeding 2 million were studied.

For each city we obtained the AOD and the cloud fraction data from GIOVANNI website.

GIOVANNI – GES-DISC Interactive Online Visualization ANd aNalysis Infrastructure.

GES DISC – Goddard Earth Sciences Data and Information Services Center

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Methodology and data continued

MODIS and MISR have quite a limited opportunity to view aerosols if cloud cover is higher than 0.8. Thus, in order to minimize the AOD retrieval uncertainty, AOD data were used only for months with cloud fraction less than 0.7.

In order to ensure that satellite aerosol sensors could differentiate between AOD over megacities and over surrounding rural areas, an 8-year mean AOD distributions over 26 megacities were analyzed (> 10 million).

Thereafter the AOD trends were estimated both over the 58 largest cities in the world (>5 million) and also over 189 largest cities in the world (> 2 million).

Latitudinal distribution of AOD - 13 megacities (a) MODIS - Terra (b) MODIS – Aqua(8-year normalized mean)

Results

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Latitudinal distributions of a normalized AOD averaged over the top 26 megacities.

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Time periods Jul 2002 – Jun 2006 Jul 2006 – Jun 2010

The averaged AOD mean

A B

Calculation of the AOD trend

values [%]

Separation of the AOD trends into groups by sign and size of

the change

The decreasing tendency (C<0)

The increasing tendency (C>0)

(-5) - 0 0 - 5

(-5) - (-10) 5 - 10

< (-10) >10

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The global distribution of the AOD tendencies during the 8-year period 2002-2010, based on MODIS-Terra

58 megacities (>5 million)

The global distribution of the AOD tendencies over the largest cities in the world

MODIS Terra

MISR

The global distribution of the AOD tendencies over the largest cities in the world

MODIS Terra

MODIS Aqua

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The global distribution of the AOD tendencies during the 8-year period 2002-2010, based on MODIS-Terra

189 megacities (>2 million)

The global distribution of the AOD tendencies over the largest cities in the world

MODIS Terra

MISR

The global distribution of the AOD tendencies over the largest cities in the world

MODIS Terra

MODIS Aqua

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The distribution of the AOD tendencies for each of the three sensors

Sensor AOD tendencyLatitudinal zones

Total45°S-15°S 15°S-15°N 15°N-45°N >45°N

MODIS Terraincreasing tendency 1 (5%) 9 (36%) 55 (44%) 4 (19%) 69 (37%)

decreasing tendency 18 (95%) 16 (64%) 69 (56%) 17 (81%) 120 (63%)

MODIS Aquaincreasing tendency 10 (53%) 13 (52%) 82 (66%) 9 (43%) 114 (60%)

decreasing tendency 9 (47%) 12 (48%) 42 (34%) 12 (57%) 75 (40%)

MISRincreasing tendency 8 (42%) 11 (44%) 69 (56%) 8 (38%) 96 (51%)

decreasing tendency 11 (58%) 14 (56%) 55 (44%) 13 (62%) 93 (49%)

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ConclusionsSpace-born sensors MODIS and MISR seem to be

capable to differentiate between AOD over megacities and over surrounding rural areas.

The increasing AOD tendencies were observed over the majority of sites in the Indian subcontinent, the Middle East, North China, and in the countries of the Gulf of Guinea.

The declining AOD tendencies were dominant over the sites in Europe and the east part of North America, where effective air quality regulation has been established.

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Conclusions continued

All three sensors (MODIS - Terra, MODIS - Aqua and MISR) show similar results of predominant AOD tendencies over all the aforementioned areas.

It was found that, overall the trends are:

(1) MODIS-Terra trends tend to be more negative (63%),

(2) MODIS-Aqua has a shift to more positive trends (60%) (3) MISR has approximately equal number of increasing and declining AOD trends