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Using GIS Interpolation Technique to
Assess Urban Air Quality and Evolve
Remediation Strategies
Riyan Habeeb, Sana Javaid
Introduction
Unprecedented urbanization in India has triggered many ill effects
on the built environment. Air pollution is one of the critical factors
that have arisen owing to unregulated urban development. Poor air
quality adversely affects health and life expectancy of citizens, natural
flora-fauna and may lead to extreme climatic events such as erratic
precipitation. Poor air quality is a major threat to human wellbeing
leading to reduction of lung capacity in adults, eye irritation, fatigue
and shortening of life span resulting from respiratory disorders or
cardiovascular diseases (WHO, 2005). In children the effect is worse
with irreversible lung damages such as bronchitis and asthma well
as increased risk of autism, epilepsy and even diabetes (WHO, 2005).
In ninety percent of the cases the disorders arise from traffic related
pollution in the vicinities(Brauer, et al., 2007).Air pollution is also
hazardous to the natural flora, fauna and environment as well. The
study on roadside trees conducted by Chauhan (2010) demonstrated
that vegetation exposed to automobile exhaust or in air polluted areas
had decreased chlorophyll, moisture, pH, carotenoid and ascorbic
acid content as compared to those away from polluted sites, indicating
224 Advancement in Basic and Applied Sciences
inhibitions arising in vegetation due to air pollution. Increasing
content of air pollution will lead to higher climate extremities in
urban areas due to addition of greenhouses gases and Urban Heat
Islands. In addition to this, high amount of suspended particles lead
to heavy condensation of moisture leading to extreme rainfall events
such as urban flooding (Rosenfeld, et al., 2008). Hence, there is a rising
concern of air pollution and its impacts on the both natural and built
environment, and humans nonetheless.
In this regard it is imperative to identify the areas of the city
in which air quality is critical, its causes and what preventive
and curative measures can be taken to mitigate the ill effects of air
pollution. To ascertain ambient air quality, four criteria air pollutants
namely, Sulphur-dioxide (SO2), Oxides of Nitrogen (NOx), Suspended
Particulate Matter (SPM) and Respirable Suspended Particulate Matter
(RSPM) are considered (Prevention and Control of Pollution Act, 1981
amended 1988). To maintain ambient air quality various concentration
levels of these criteria are standardized by Central Pollution Control
Board (CPCB), which states 60 mug/cum for PM10, 50 mug/cum for
SO2 and 40 mug for NO2 in Residential, Commercial and Industrial
Areas, while 60 mug/cum for PM10, 20 mug/cum for SO2 and 30 mug
for NO2 in Sensitive Areas. A major concern for pan city assessment of
air quality is limitation of monitoring stations which hinters in micro-
analysis in city areas for critical air quality as the stations are often
placed at fewer junctions and discretions. GIS modeling can present a
solution to these issues with their tools in mapping urban air pollution
throughout the city with the help of few weather stations.
Taking Dehradun as a case study, the paper attempts to investigate
air pollution levels at various junctions of the city with selected criteria
pollutants - NO2, SO2 and PM10 levels to assess pan city urban air
quality using GIS interpolation technique. Thus enabling formulation
of remediation strategies which can aide in improvisation of air
quality and remediation of affected urban areas.
Data Sets & Methodology
For the study data was collected from various institutional bodies,
it included, Municipal and Ward boundaries for area demarcation of
Dehradun Municipal Corporation, and Census 2011 data to analyse
ward wise population. Environmental data with respect to air quality
and pollution from Uttarakhand Environment Protection & Pollution
Control Board (UEPPCB). The air quality statistical data (NO2, SO2,
Using GIS Interpolation Technique to Assess Urban Air… 225
PM10) was available for three locations in Dehradun namely ISBT,
Clock Tower and Raipur which is used in the analysis. Also, satellite
imagery data was used to generate for Digital Elevation Model (DEM)
to understand the topography of the city and Land Use Land Cover
Change in Doon Valley.
The data sets collected for three junctions were first statistically
compared with pollution standards to assess their criticality and
historical trend of the pollutants. For spatial analysis QGIS Modeling
platform was used in preparation of ward-wise base map of
Dehradun and geo-referenced. The wards were linked with census
population data to understand spatial distribution of population
in city’s administrative wards. This was followed by determining
location of weather stations’ junctions namely as points in GIS-model
and then inputting latest levels of PM10, SO2, and NO2. Since recording
stations were installed at selected locations, in order to assess over
all air quality throughout the city, interpolation technique was used
to fill the data gaps for all the wards. Interpolation is a commonly
used GIS technique to create continuous surface from discrete points.
The interpolation technique gave an overall air contour map for the
city, which was then collated with the wards and there population to
identify exposed areas. Finally, area specific strategies were identified
and recommended to aid in environmental remediation.
Study Area Prole: Dehradun
Dehradun is located between latitudes 29 °58’N and 31°2’N
and longitudes 77° 34’ E and 78° 37’E. The region is bounded by the
Himalayas from the north, Ganges River from the East and Yamuna
River from the west. As per Census of India 2011, Dehradun city has
a population of 578,420 inhabitants. The city demonstrates a high
literacy rate (84.25%) in comparison to Uttarakhand state (79.63%)
and overall country (74.04%). The population growth rate is 32%
well above the national (18%) and state (17%) levels. Also, rate of
urbanization in the district is much higher than the national and state
average making it largely an urban area.
Urbanization Trends
Dehradun City has shown high progressive growth especially
over the past two decades. At present the area of the city is about
64.4 m2 out of which larger part is residential followed by institutional
226 Advancement in Basic and Applied Sciences
and commercial spaces. General terrain of the city is largely plain
which is gradually adulating from South to North. Digital Elevation
Model (DEM) as represented in Figure-1 shows the city to be more
skewed in North and less as one moves towards the South. North
being mountainous tract while the lowland south being more planar
making it more suitable for new settlements and social activities.
Figure 1: Digital Elevation Model (DEM) & Ward-wise Population
(Source: Author, generated from CARTOSAT Satellite Data Set; Ward
boundary with population data from Census of India 2011, Dehradun
Nagar Nigam)
After formation of Uttarakhand Dehradun city has implemented
large to small scale economic reforms in the form of industrial areas,
this has led to a very drastic change in land use and land cover
pattern of the city. Studies conducted by various researchers in the
field show Land Use Land Cover (LULC) change from 1987 up to 2008
through Remote Sensing (RS) imagery at periodic difference of five
years namely 1987, 1992, 1998, 2003, 2008. The study observes that
there has been steady growth in the urban built-up area and during
2003-08 it has almost doubled as compared to 1998-2003 (Gupta,
2013). In statistical analysis of LULC from 2000-2009 undertaken by
researchers (Kuldeep & Kamlesh, 2011), using RS techniques presents
the statistical evaluation of the land for classes namely - Forest,
Agriculture, Barren/ Scrub, Built-Up And Water, shows considerable
decrease in natural cover while greater increase in Built-up. (Table-1)
Using GIS Interpolation Technique to Assess Urban Air… 227
Table 1: Statistics of LULC 2000-2009 (Source: Tiwari & Kuldeep, 2011)
Land Use class 2000 (%age) 2009 Change area
Forest 57.98 55.85 -3.75
Agriculture 33.06 32.66 -1.3
Barren/Scrub 6.57 7.30 10.09
Built-up 1.67 3.56 112.4
Water 0.70 0.64 9.5
Similarly LULC compared between year 2005-06 and 2011-2012 (Fig-
2) shows a comparative LULC illustrating South-West development
encroaching agricultural land.
Figure 2: Comparative LULC 2005-06 & 2011-12 Over Various LULC
Classes (Source: Author, Based on Bhuvan Satellite Data)
228 Advancement in Basic and Applied Sciences
Ambient Air Quality
There are three air monitoring sites in Dehradun - Clock Tower
at City Centre, Interstate State Bus Terminal (ISBT) and Raipur Road.
As per data from UEPPCB the air is monitored for mainly three
components Particulate Matter (PM10), Nitrogen-di-oxide (NO2) and
Sulphur-di-oxide (SO2). The containment of air with these elements
varies with the distinction of area as General or Sensitive as declared
by the board. All of these areas fall under sensitive zones – Clock
Tower as Commercial Sensitive, ISBT as Industrial Sensitive and
Raipur as Residential Sensitive Zone. Latest year 2017 recording were
taken to cumulatively assess all the three locations with respect to the
air components (Fig.3). Exceedence Factor or EF was used to assess
the criticality of pollutants, which is the ratio of existing concentration
of criteria pollutant to the respective pollutant concentration
standard. Based on EF four broad categories of pollution are classified
as Critical Pollution (Where EF>1.5), High Pollution (Where EF is
between 1.0-1.5), Moderate Pollution (Where EF is between 0.5-1.0)
and Low Pollution (Where E < 0.5). In all the locations PM10 was
found significantly greater than Critical pollution levels (EF>1.5) with
average value of 230 mug/cum, in comparison to standard levels.
The worst case being at ISBT followed by Raipur Location and Clock
Tower respectively. Similar trends were observed for So2 and No2,
except the exceedence in pollution was not as high as PM10, however,
based on EF (1.0<EF<1.5) the locations can be categorized in High
Pollution Levels. Here again, highest pollutions were found at ISBT
than Raipur Road and Clock Tower respectively.
Similarly the ambient air quality data for past ten years were to be
assessed for all the three components at Clock Tower (only location
with historical data). PM10 has remained at critical pollution levels
(Fig.4). Similarly SO2 levels have been higher than the prescribed
compliance standards. NO2 levels have shown an incremental trend
since 2011. Except NO2 levels, the concentration of other two elements
have remained well above permissible levels.
From figures-3&4 it is evident that the concentration of PM10 is
very high at all the locations as compared to the CPCB standards
and others also show relative high concentration in comparison with
permissible standards. Among all the three locations ISBT has highest
levels of PM10, SO2, NO2 concentrations followed by Clock Tower and
Raipur Road, thus making it the most polluted site with respect to
ambient air quality.
Using GIS Interpolation Technique to Assess Urban Air… 229
Figure 3: Location Wise Concentration of Impurities Compared with
CPCB Standards (Source: Author, based on UEPPCB Data)
Figure 4: Year wise Ambient Air Quality and Permissible Levels at Clock
Tower (Source: Author, based on UEPPCB Data)
230 Advancement in Basic and Applied Sciences
The high amount of air impurities can be directly linked to
vehicles since all the industries are located outside Dehradun. This
is coupled with ISBT being inter-state bus station, thus adds to
the pollutant levels. Clock Tower being second to ISBT is again an
unavoidable critical cross junction between the city connecting North,
South, East and West limits of the City. Limited infrastructure and
public transport system’s failure to meet the environmental standards
as well as high ownership of private vehicles can be directly linked
to the air pollution levels. Hence, the unchecked development, lax
regulations for vehicles can be attributed to the deterioration of
ambient air quality.
Air Contour Map
Since the air components data was available for only selected
locations, in order to assess overall ambient air quality for Dehradun
city GIS interpolation technique was used to draw overall pan city
air contour map. The analysis gives an overall assessment level
of air components over the map boundary. Figure-5 indicates the
interpolated map derived from air data at aforementioned three
locations leading to overall contoured air quality over the chosen
geographical boundary. The central points of location being highest
followed by decreasing value of the contours as one moves away from
critical location thus denoting the value for each pollutant level. Their
interpolated value is generated automatically by GIS.
To assess area and population affected by pollution, ward-wise
population map was overlaid with the contour map to exact critical
levels in the city (Fig.6). From the map it is clear that wards on the
south west region of city, especially those proximate to ISBT have
poorer air quality than rest of the wards, though rest of the city still
contains high pollution levels as well. Critical air quality can be found
in Wards - 42, 43, 44, 46, 47 exceeding beyond standard limits of all
levels. These wards also contain high number of population since
the city has grown towards its south more than north owing to its
geographical limitations.
Through this technique, although it is possible to roughly aggregate
the level of air components, hence the air pollution, it is to be noted
that the values derived from contours are based on the assumption
that the scene over which contours are laid remains unhampered by
any local physical proactive or counter active elements present in the
vicinity of the area. Presence of any physical element such as trees
Using GIS Interpolation Technique to Assess Urban Air… 231
or structure can either decrease or increase the air quality owing to
their properties, while green spaces and trees can positively affect
air quality, buildings and structures because of their occupancy will
negatively affect the air quality. Since it is also not possible to install
remote observation stations at every location, this technique can be
useful in first hand general assessment of overall ambient air quality
followed by onsite visitation to highlighted areas to gather local air
data and verification.
Figure 5: Ambient Air Quality Interpolated Contour Map (Source:
Author, based on UEPPCB Data)
Issues and Interventions
From the above analysis it is quite evident that Wards - 42, 43, 44,
46, 47 associated with ISBT, Clock Tower face chronic air pollution
exceeding beyond standard limits due to transit and commercial nature
of the areas attracting lot of traffic. If continued the deteriorating air
quality shall lead to following adversaries:
232 Advancement in Basic and Applied Sciences
Table 2: Ambient Air Quality - Present Scenario and Future Impacts
Present Issues Future Impacts
High content of pollutants
making the natural air less
breathable
Deterioration of Urban
Environment and Health Hazard
leading to asthma and other
bronchitis related issues.
High amount of Green House
Gases being released into the
city’s atmosphere
Rise in climate extremities due to
increased greenhouse goes like
increase in extreme temperatures.
Generation of Smog Heavy smog will affect the
visibility on the roads making
them prone to road causalities, as
well as obstructing beautiful hill
surroundings of the valley.
Figure 6: Overlaid Contours Over Wards Map
(Source: Author’s Analysis)
To counteract such issues in affected areas following are some
recommendations for interventions at city level and critical locations:
1. Discouraging plodding of private and high polluting vehicles
by providing effective and eco-friendly public transport.
Promotion of Non-motorized Transport (NMT) such as
Using GIS Interpolation Technique to Assess Urban Air… 233
Pedestrian and Bi-cycle Lanes at various locations affected
by high pollution levels and those prone to it such as Clock
Tower and Raipur Area.
2. Re-routing of origins and destinations, especially those
passing through Clock tower or CBD of the city by planning
alternative routes for transportation as currently it’s the only
junction responsible for North-South-East-West Transit.
3. Urban greening of areas with trees of high pollution tolerance
in areas/ wards most affected by poor air quality. Air
pollution tolerant index (APTI) is an index denotes capability
of a plant to combat against air pollution. Plants which have
higher index value are tolerant to air pollution and can be
planted as sink to mitigate pollution, while plants with low
index value which show less tolerance and can be used to
indicate levels of air pollution(Narwaria & Kush, 2012) in
absence of air quality monitoring system.
4. Planning of Landscape Park around ISBT with high APTI
vegetation can help mitigate air pollution arising due to
buses, and auto-rickshaws. This can curtail and limit spread
of onsite pollution to negihbouring areas as well.
5. To arrest further degradation of air quality, introduction
of Green Plot Ration (GnPR) (Ong, 2003) for new building
constructions. GnPR is a qualitative and quantitative measure
of effective greenness on a site. It is based on a common
biological parameter called leaf area index (LAI – single side
leaf area per unit ground area). Green plot ratio is an average
LAI of greenery on site.
6. These strategies and interventions can cumulatively lead to
remediation of air quality not only at specific areas but will
also help in city wide improvement of air quality.
Conclusion
With challenge of deteriorating urban air quality leading to both
environmental and health hazards, it is requisite to incorporate latest
technologies and analytical tools to evaluate the rising degradation
of our natural and urban environment. It is also imperative to use
analytical tools such as GIS to fill the void created either by situational
or authoritative factors, implying better assessment of our urban
environment resulting in derivation of intervention measures thereof.
234 Advancement in Basic and Applied Sciences
The study therefore interlinked urbanization and air pollution in
conjugation with location specific counters. It is also evident from the
study that vehicles are by far the most responsible for degradation
of urban air quality. As urbanization leads to better spending power
and require transport for daily activities, planning for environment
friendly public transport and NMTs will not only discourage owning
private vehicles but will also lead to better traffic management
curtailing air pollution. Where there is no option for such curtailment,
such as ISBT, vegetation can be used as effective measure to counter
air pollutants. Given the eco-sensitive nature of Dehradun city, it is
requisite to plan for better air quality management strategies and
evolve new tools to assess the same.
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