IAAR Seminar 21 May 2013 AOD trends over megacities based on space monitoring using MODIS and MISR Pinhas Alpert 1,2, Olga Shvainshtein 1 and Pavel Kishcha 1 1 Department of Geophysical, Atmospheric and Planetary Sciences 2 Porter School of Environmental Studies Tel Aviv University Alpert, 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. 1

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, , doi: /ajcc Published Online September 2012 ( Can also be downloaded from my Publications Website: 2

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. 3

The sensors MODIS (Moderate Resolution Imaging Spectroradiometer) MISR (Multi-angle Imaging SpectroRadiometer) Resolution (degrees) 1×11×10.5×0.5 Global coverage time Every 1-2 daysEvery 9 days Equator crossing:Terra a.m. – local time (north to south) Aqua a.m. – local time (south to north ) a.m. – local time (north to south) View angles1 angle9 different angles MISR 4

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 5

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). 6

Latitudinal distribution of AOD - 13 megacities (a) MODIS - Terra (b) MODIS – Aqua (8-year normalized mean) 7 Results

Latitudinal distributions of a normalized AOD averaged over the top 26 megacities. 8

Time periodsJul 2002 – Jun 2006Jul 2006 – Jun 2010 The averaged AOD mean AB 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) (-5) - (-10) < (-10)>10 9

The global distribution of the AOD tendencies during the 8-year period , based on MODIS-Terra 58 megacities (>5 million) 10

The global distribution of the AOD tendencies over the largest cities in the world MODIS Terra MISR 11

The global distribution of the AOD tendencies over the largest cities in the world MODIS Terra MODIS Aqua 12

The global distribution of the AOD tendencies during the 8-year period , based on MODIS-Terra 189 megacities (>2 million) 13

The global distribution of the AOD tendencies over the largest cities in the world MODIS Terra MISR 14

The global distribution of the AOD tendencies over the largest cities in the world MODIS Terra MODIS Aqua 15

The distribution of the AOD tendencies for each of the three sensors SensorAOD tendency Latitudinal zones Total 45°S-15°S15°S-15°N15°N-45°N>45°N MODIS Terra increasing tendency1 (5%)9 (36%)55 (44%)4 (19%)69 (37%) decreasing tendency18 (95%)16 (64%)69 (56%)17 (81%)120 (63%) MODIS Aqua increasing tendency10 (53%)13 (52%)82 (66%)9 (43%)114 (60%) decreasing tendency9 (47%)12 (48%)42 (34%)12 (57%)75 (40%) MISR increasing tendency8 (42%)11 (44%)69 (56%)8 (38%)96 (51%) decreasing tendency11 (58%)14 (56%)55 (44%)13 (62%)93 (49%) 16

Conclusions Space-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. 17

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 18