Remote Sensing of Environment and Disaster Laboratory

Institute of Industrial Science, The University of Tokyo, Japan

Analyzing the Effect of Urbanization on Air
Quality in Colombo, Sri LankaphotoLilangi Varunika Wijesinghe, Wataru Takeuchi

Institute of Industrial Science, The University of Tokyo, Japan
Abstract: Long-term aerosol concentration variations have been assessed on global and regional scales as it is an important input for the11.6: “Reducing impact ofadverse air quality onenvironment”

studies related to air pollution, climate change and Earth radiation budget. Air pollution has become a serious environmental problem in many
cities of developing countries. Sri Lanka is not an exemption. This study analyses the temporal variations of Aerosol Optical Depth (AOD)
retrieved by Moderate Resolution Imaging Spectroradiometer (MODIS) to understand about aerosol concentration variation in Colombo, SriLanka. Furthermore, this study uses AirRGB product for urban air quality characterization. The increasing AOD trend includes urban air
pollution rise in Colombo District. However, having B values higher than 50 most of the time highlights that air is cleaner. G and R valuesrepresents anthropogenic urban aerosols. G value shows a clear seasonality trend having higher values from September to March followed bylower values in wet season. Higher G values can be due to the contribution of biomass burning which takes place during every September toOctober period as a result of field preparation for main cropping season. The three main land-use types in Colombo district are residential,industrial and commercial. Considering the urban morphology changes which took place from 2001 to 2018, it can be concluded that theexpansion of residential area was the highest from 85% followed by industrial area expansion from 14%.

2. DATA & METHODOLOGY

1. INTRODUCTION
Air pollution has become a serious environmental problem in many cities of developing countries.
Sri Lanka is not an exemption. Colombo is the capital city of Sri Lanka which has the highest rate ofurbanization and industrialization.
• Sri Lanka is undergoing rapid urbanization and industrialization- By 2050, estimated urban population is 34%- GDP is increasing while energy consumption also increases- Level of industrialization in Sri Lanka is relatively low- Vehicle population is increasing

Landsat 5,7,8

AW3D DSMAirRGB trend analysis

Built-upnDSM

Back trajectory analysis
HYSPLIT(Misra, P. 2018)

Urban morphology maps (2001-2018)
Residential, Commercial, Industrial

Rise in air pollution(ADB, 2006 & CAI-Asia, 2008)

Spatial allocation of emissions fromLU types

US Embassy
Colombo airquality data
Impact due to socioeconomic development(GDP, Vehicle population

Quantification of transboundary
contribution to urban air quality

Assessing the impact on urban air quality in Colombo District, Sri Lanka

Figure 4: Study area

Figure 3: Flowchart of the study

Table 1: Datasets used in the study

Figure 2: Vehicle population growth between 1991and 2007

Figure 1: Urbanization increase between 1990 and 2005
and forecast for 2050

DatasetProductSpatial
Resolution

DatasetDuration

MODIS

Deep_Blue_Aerosol_Optical_De
pth_550_Land

10 km

2001 - 2018

Landsat

Landsat 5, 830 m

2001 - 2018

4. RESULTS & DISCUSSION
4.3. Urban morphology map

4.1 Time series of monthly mean AOD• Three main land-use
types in Colombo
district are residential,industrial andcommercial

1000
900800AOD * 1000700
600
500
400
300

y = 0.7694x + 369.55

2001002001-01
2001-05
2001-09
2002-01
2002-05
2002-09
2003-01
2003-05
2003-09
2004-01
2004-05
2004-09
2005-01
2005-05
2005-09
2006-01
2006-05
2006-09
2007-01
2007-05
2007-09
2008-01
2008-05
2008-09
2009-01
2009-05
2009-092010-01
2010-05
2010-09
2011-01
2011-05
2011-09
2012-01
2012-05
2012-09
2013-012013-05
2013-09
2014-01
2014-05
2014-09
2015-01
2015-05
2015-09
2016-01
2016-05
2016-092017-012017-05
2017-092018-012018-05
2018-090

Figure 5: Time-series of monthly mean AOD 2001 - 2018
Figure 7: Urban morphology map for Colombo District - 2018

• Considering the urban
morphology changes
which took place from2001 to 2018, it can beconcluded that theexpansion of residential
area was the highest
from 85% followed byindustrial area
expansion from 14%

4.2 Urban air quality characterization
10090• According to the AirRGB data, it can be concluded that the urban air quality in
Colombo is cleaner as most of the time B > 50

807060• There is a clear seasonality in the variation of G value when 4-month moving average
pattern was considered, having higher values from September to March followed bylower values in wet season

50
40
30
20
10

2001-1
2001-4
2001-7
2001-10
2002-1
2002-4
2002-7
2002-10
2003-1
2003-4
2003-7
2003-10
2004-1
2004-4
2004-7
2004-10
2005-1
2005-4
2005-7
2005-10
2006-1
2006-4
2006-7
2006-10
2007-1
2007-4
2007-7
2007-10
2008-1
2008-4
2008-7
2008-10
2009-1
2009-42009-7
2009-10
2010-1
2010-4
2010-7
2010-10
2011-1
2011-4
2011-7
2011-10
2012-1
2012-4
2012-7
2012-10
2013-1
2013-42013-7
2013-10
2014-1
2014-4
2014-7
2014-10
2015-1
2015-4
2015-7
2015-10
2016-1
2016-4
2016-7
2016-10
2017-12017-42017-72017-10
2018-1
2018-42018-7
2018-100RG• G can be anthropogenic emissions (vehicular emissions, biomass burning) to urbanaerosols. Rising aerosol concentration in September each year can be due to thebiomass burning which takes place during field preparation for main cropping season(Maha) which is a seasonality activity

B

Figure 6: AirRGB Variation from 2001 - 2018

5. REFERENCES[1] M. Mehta, R. Singh, A. Singh, N. Singh, and Anshumali, 2016. “Recent global aerosol optical depth variations and trends - A comparative study using MODIS and MISR level 3 datasets,” Remote Sens. Environ., vol. 181, pp. 137–150[2] Y. Luo, X. Zheng, T. Zhao, and J. Chen,2014. “A climatology of aerosol optical depth over China from recent 10years of MODIS remote sensing data,” Int. J. Climatol., vol. 34, no. 3, pp. 863–870

For further details, contact: Ms. Lilangi Wijesinghe, Bw-601, 6-1, Komaba 4-chome, Meguro, Tokyo 153-8505 JAPAN (URL: http://wtlab.iis.u-tokyo.ac.jp/ E-mail: lilangi@g.ecc.u-tokyo.ac.jp)