Location selection of sensor based monitoring systems

LOCATION OF LOW-COST
SENSOR-BASED AIR QUALITY
MONITORING DEVICES
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Monitoring the pollutant concentration is fundamentally important to develop and evaluate pollution control
strategies. It enables us to understand the trend and extent of pollution by identifying pollution sources, and
thereby indicating where more efforts are needed.
It is important to ensure that the measured air quality provides adequate and accurate information. One of the key
factors affecting the accuracy of monitoring data is the location and placement of the air quality monitoring
device.
Inappropriately placed monitors lead to inaccurate measurement of pollutant concentration, which may not meet
the data quality required for the given objective.
Site selection is carried out by assessing various factors like scope of monitoring, meteorological conditions,
topography of the region, availability of space, distance from the source, presence of various obstructions, etc.
SCOPE OF
MONITORING
METEOROLOGICAL
CONDITIONS
TOPOGRAPHY SPACE
AVAILABILITY
DISTANCE
FROM SOURCE
INTRODUCTION Location of sensor-based air quality monitoring devices

REPRESENTATIVENESS COMPARABILITY
To avoid influence by the sources that are not
being investigated, it is important to select a site
that is representative to the sources of interest.
Also, in order to carry out trend analysis, the
selected site should remain representative for a
long time.
A standardized procedure of location selection must be
followed to enable comparison of monitoring data with
past monitoring data and data from other monitoring
sites.
This facilitates trend analysis and provides accurate on
pollution conditions in space and time.
PRINCIPAL FACTORS Location of sensor-based air quality monitoring devices

A preliminary survey is carried out at the area of interest to better understand local factors affecting quality of
monitoring. Such surveys help us in better understanding presence of local emission sources, population
distribution in the region, land-use pattern, etc. Such details about the prospective monitoring site guides in the
choosing the right spot for monitoring.
LOCAL EMISSION SOURCES
Understanding of local emission sources helps
in avoiding monitoring locations which may
have higher influence from surrounding
emissions.
POPULATION DISTRIBUTION
Population distribution data helps in assessing
the pollution exposure on people.
LAND-USE PATTERN
Land-use pattern creates a better
understanding of the type of built-up
environment which is present in the
region.
TOPOGRAPHY OF THE REGION
Local topographical features should be taken into
consideration as they are able to alter local
meteorological conditions and pollutant
distribution.
METEOROLOGICAL CONDITIONS
The general meteorological conditions should be
evaluated to understand predominant wind-direction
and usual wind-speed, temperature, relative humidity
etc.
LOCAL SITE-SPECIFIC FACTORS
Prospective site should be evaluated for availability of
space, electricity, and must be free from any kind of
obstruction.
PRELIMINARY SURVEY Location of sensor-based air quality monitoring devices

SPATIAL SCALE OF URBAN MONITORING
Micro to middle scale (0.5 km to 4 km)
If the objective is to understand human exposure to
pollution, the monitoring station should be placed in
the human breathing zone at the height of 2-4 m.
If the objective is to understand the background
pollution or pollution trends of the region, the
monitoring stations should be outside the influence
zone of any direct emission sources at the height of 10-
14 m.
To avoid pollution spikes from traffic it must be placed
minimum of 50 m away from nearby roadway. It should
also be at least 100 m away from any other source of
emission.
VARIOUS OBJECTIVES OF MONITORING
• Understanding background pollution levels
• Pollution trend
• Exposure to people
BACKGROUND
MONITORING
Location of sensor-based air quality monitoring devices

The study location should be selected to provide easy interpretation
of roadway source contribution and should be able to accurately
capture periodic pollution spike which is expected while measuring
vehicular pollution.
Monitor placed within 5-10 m from the roadway is expected to record
representative concentration of traffic.
Unless the road intersection is the specific objective of monitoring, it
is advisable to not conduct monitoring at intersections, and instead
should be carried-out mid-way along the block.
The height of the monitor should not exceed 10 m.
ROADSIDE MONITORING Location of sensor-based air quality monitoring devices

Usual gaseous emissions from dump-yard / landfill include
gases such as methane (CH4), carbon dioxide (CO2), hydrogen
sulfide (H2S), methyl mercaptan (CH3SH), sulfur dioxide (SO2)
etc.
Gas monitoring is usually carried out within the waste-body
and on the periphery of the landfill site, odour monitoring is
usually carried out only on the periphery to avoid odour
diffusion from the dump-yard / landfill.
Also, odour monitors should be placed in the vicinity, if
sensitive receptors such as residential areas, schools etc are
present.
ODOUR AND GAS MONITORING Location of sensor-based air quality monitoring devices

Gases such as methane (CH4), hydrogen sulfide (H2S), methyl
mercaptan (CH3SH), ammonia (NH3), formaldehyde, total volatile
organic carbon (TVOC), chlorine gas, etc. are the common cause
of odour pollution.
Common sources of odour at water and wastewater treatment
plants are equalization tank, digesters, aeration tanks, skimming
tank, drying beds etc. In case of industries, odour sources
depend upon the type of industry.
Sources should be identified during the preliminary survey and
the odour monitor should be installed in the downwind
direction to the source.
It should be placed within 10 m of the source and the height
should be 3-8 meter or more, depending on the height of the
source.
ODOUR MONITORING Location of sensor-based air quality monitoring devices

The main objective of air quality monitoring in tunnels or
underground parking lots is to understand whether the
ventilation systems are working as planned or not, to assess the
visibility level in order to avoid accidents, and to carry out
exposure studies.
Parameters of interest for tunnel monitoring are, visibility, NO,
NO2, CO and particulate matter.
To get representative concentration, air quality monitoring
should be carried out in the ventilation stacks, as well as at the
ground locations. It should be placed both, on the roof and
roadside locations to get representative concentration.
In case of underground parking facilities, at least one
monitoring device should be provided at each entrance and
exit points. Inlet port must be placed at a minimum distance of
1.8 m above the floor surface.
TUNNEL MONITORING Location of sensor-based air quality monitoring devices

Aviation industry emits high concentrations of NO2, SO2, Volatile
Organic Compounds (VOC), and unburnt hydrocarbons. As a result,
ground level pollution due to landing and take-off (LTO) is of
particular concern for airports along with the background
concentrations due to vehicular and domestic emissions.
Site 1: For background concentration measurement
Site 2: (Both 2a & 2b) Intense airport activities like aircraft handling,
infrastructure, take-off and landings, etc.
Site 3: Residential area downwind to the airport
Site 4: Next to a major traffic road to study road traffic impacts
Site 5: Another residential area downwind of an industrial area to
discriminate between airport and industrial emissions.
Site 6: Station is located further downwind from the airport for
general monitoring purposes.
Source: Airport Air Quality Manual, International Civil Aviation Organization.
AIRPORT MONITORING Location of sensor-based air quality monitoring devices

MINING & CONSTRUCTION MONITORING
Dust, sand, ashes, and saw-dust are the major pollutants at
mining and construction sites. Due to larger site areas, both
fixed and optional mobile monitoring stations can be
provided over the site and on the site perimeter.
The location of stations should be selected based on the
meteorological data(downwind and upwind conditions),
topographical features, environmentally and ecologically
sensitive targets.
In case of construction sites, the monitoring stations are
placed on the periphery of the site.
Off-site monitors are placed in the downwind location as
receptors. Fixed/Mobile monitors are placed inside the site
for exposure monitoring.
The sampling height should be more than 2 meters from
the ground.
Location of sensor-based air quality monitoring devices

After finalizing the site for the monitoring, there are few local factors that should be considered in order
to measure representative pollutant concentration.
OBSTRUCTION
Obstruction due to buildings, walls, trees causes a change in wind speed and
direction and blocks the air, which generates erroneous data.
OVERHANG / SHADOWS
Shadows must be avoided from; overhanging foliage, roofs, sheds, buildings,
walls etc. for accurate measurement of pollutant concentration.
MOBILE TOWERS / EMF TOWERS
Sensor performance may get interfered due to electromagnetic forces (EMF)
from mobile towers.
POWER SOURCE
Electricity source should be present near the monitoring device for power
supply. However, in the absence of a power source Oizom devices can also
operate on solar energy. Solar panel can be installed at the pole itself.
LOCAL / SITE SPECIFIC FACTORS Location of sensor-based air quality monitoring devices

Location selection of sensor based monitoring systems

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