Olalekan Popoola , Iq Mead , Vivien Bright , Ronan Baron , John

A Portable Low-Cost High Density Sensor Network for Air Quality at London
Heathrow Airport
Olalekan
*(1)
Popoola ,
Iq
(1)
Mead ,
Vivien
(1)
Bright ,
Ronan
(2)
Baron ,
John
(2)
Saffell ,
Gregor
(1)
Stewart ,
Paul
(3)
Kaye ,
(1) Department of Chemistry, University of Cambridge, UK
(2) Alphasense, Sensor Technology House, Great Notley, UK
(3) Sensor & Technology Research Institute, University of Hertfordshire, UK
1. SNAQ HEATHROW PROJECT
(a) Objective
(b) Instrumentation
• Deployment of state-of-the art network of pollution sensors
(SNAQ sensor nodes) in and around LHR airport.
• Establishing pollution data for science and policy studies
• Comparing data with emission inventories and pollution
models.
• Source attribution for LHR airport.
• Creation of novel tools for data mining, network calibration,
data visualisations and interpretation.
• Optimisation of sensor network for different environments.
• Gas phase species:
 CO, NO, O3, SO2, NO2 (electrochemical
(EC) at 2 s)
 CO2 and total VOCs (optical at 10 s).
• Size-speciated particulates (0.38 to 17.4 µm,
optical (OPC) at 20 s)
• Meteorology (sonic anemometer).
• GPS and GPRS (position and real time data).
• Temperature and RH
* [email protected]
‡ [email protected]
3. PRELIMINARY RESULTS SNAQ HEATHROW DEPLOYMENT
(a) Snapshot of measurements across the network
PM2.5
Anemometer
and Roderic
‡
(1)
Jones
SNAQ32
SNAQ32
PM2.5
GPS and GPRS
LHR daily operating cycle – aircraft movements
OPC inlet
CO
CO
OPC
Main Board
Temp & RH
EC sensors
~49 x 22 x 16 cm. ~2.8 kg
PM2.5
PM2.5
Northern runway
~ 2.75 km
Time series plot showing result of a
one month and a week measurement
from one sensor node at LHR
airport. (top right).
• Airport operational mode clearly
visible in measurements (low
night-time mixing ratios
associated with switch-off
modes)
(c) Current status of SNAQ network
CO
CO
From left to right, polar bivariate plots2
of CO averaged by hours of the day,
days of the week and months of the year
(bottom right) of a sensor node located
to the NE end of the southern runway
• Airport activities minimal between
2200 hrs & 0500 hrs
• Plots show high pollution events
mainly in the NE quadrant which is
associated to take-off’s
PM2.5
PM2.5
CO
CO
Southern runway
~ 5.25 km
Plots showing sensor deployed and data captured till date
Time series plot showing PM2.5 and CO measurements at some sites in London Heathrow airport. Notice the spatial variation across the network.
• ~ 60% sensor nodes deployed (starting mid 2012)
• ~ 2107 records (CO, NO, NO2, O3, SO2, hydrocarbons, CO2, size speciated PM, meteorology) transmitted (20 sec data)
• 1-2 second data recorded on USB storage (~ 4108 records)
(b) Source attribution: northern and southern runways
High CO & NO mixing ratios (red circles) at low
WS (<5ms-1) in the NE quadrant of the plot suggest
a pollution source to the north of the sensors
(northern perimeter Road)
N
2. CHARACTERISATION: Laboratory and field measurements
CO
Field measurements of
particulates
SNAQ OPC: 30 min ave
Reference 1 (NoS) 30 min ave
Reference 2 (Grimm) 30 min ave
CO
NO
(ppb)
(ppb)
Laboratory tests of gas species
(c) Effect of meteorology on pollution mixing ratios
Northern perimeter
Road
Northern perimeter Road
Northern runway (27R)
CO
NO
(ppb)
CO
NO
N
Mixing ratio (ppb)
100
NO
80
SNAQ17
60
40
South
Easterly
20
CO
NO
(ppb)
(ppb)
North
Easterly
0
60
Mixing ratio (ppb)
High NO mixing ratios (black circles) at
high WS (>15ms-1) in the SW quadrant
of the plot suggest a pollution source to
the south-west of the sensors (aircraft
landings on the northern runway)
(ppb)
(ppb)
O3
50
Southern runway
(09R)
SNAQ48
40
30
20
10
0
-10
60
40
30
SNAQ08
– SNAQ (EC)
0.38-0.48µm
– Ratified
0.38-0.48µm
2.73-3.44µm
9 AUG., 2012
18 AUG., 2012
CO2
2.73-3.44µm
× 10
0.48-0.68µm
3.44-4.34µm
10
0
-10
Nov 14
Date (2012)
Nov 16
Nov 10
• Excellent laboratory response at ppb mixing
(top left)
• Good instrumental performance against reference techniques under ambient conditions. 15 minutes average measurements of total
particulate (top right) and gas species – NO, O3, NO2 (bottom)
ratios1
× 10
0.68-0.86µm
× 10
0.86-1.08µm
4.34-5.47µm
5.47-6.89µm
1.08-1.36µm
6.89-8.69µm
1.36-1.72µm
8.69-11.0µm
1.72-2.17µm
11.0-13.8µm
4. CONCLUSIONS AND FUTURE WORK
• First, high-temporal and spatial, long-term deployment of pollution sensor networks in LHR airport
measuring multiple gas species and particulates as well as meteorology.
• Exciting findings from preliminary results:
 Large temporal variations in mixing ratios of pollutants observed across the network. These are linked to
location of sensors and proximity to pollution sources (runways and major roads).
 Enhanced pollutant and particulate levels were observed under stable weather conditions. Specific weather
conditions such as fog events can readily be inferred from particulate measurements.
• Future work include deploying the remaining sensor nodes, comparing measurement data with dispersion
models and emission inventories.
• Detailed analysis of data using information on airport operations to apportion pollution sources
2.17-2.73µm
Oct 22
Oct 29
× 10
Concentration (cc-3)
× 10
× 10
0.48-0.68µm
Oct 29
3.44-4.34µm
0.68-0.86µm
× 10
5.47-6.89µm
1.08-1.36µm
1.36-1.72µm
1.72-2.17µm
2.17-2.73µm
Oct 22
Time series plots (top right) of CO2, CO, temperature and wind speed measurements of two SNAQ sensor nodes during (brown
shades), before and after (blue shades) an anti-cyclone condition across the UK in 1-18, August, 2012. SNAQ24 is deployed as part
of the LHR sensor network whereas SNAQ49 was used in South Kensington, Central London (~ 19 km east of LHR airport) as part
of the ClearFlo project. Synoptic weather charts showing the build-up of the anti-cyclone over these period (bottom right)
4.34-5.47µm
0.86-1.08µm
13.8-17.4µm
Oct 22
Concentration (cc-3)
20
Nov 12
2 AUG., 2012
SNAQ43
× 10
Nov 10
• Mirror image pattern (left panel)
observed in the polar bivariate plots
of the two sensor nodes (SNAQ17
& SNAQ48) deployed at the end of
the southern runway (09R).
• This suggests a common source
(southern
runaway)
located
perpendicular to the distance
between the two sensors.
• High CO & NO mixing ratios (at
high wind speeds) suggests aircraft
take-offs.
(d) London fog (20-24 October, 2012)
NO2
50
Concentration (cc-3)
Mixing ratio (ppb)
(ppb)
Oct 29
Oct 22
Memorable foggy conditions of
6.89-8.69µm 20-24, Oct. 2012 were observed
in all the particulate size range
recorded across the SNAQ
8.69-11.0µm
network in LHR airport.
11.0-13.8µm Particulate measurement from
two sensor nodes (left) and a
BBC news article3 reporting
13.8-17.4µm
flight disruption at LHR airport
Oct 29 related to this event (top).
Time series plots (top left) of CO2 and CO of six SNAQ nodes, five in LHR
airport (see map above for location) and one in Central London.
• The stable condition characteristic of anti-cyclones encourages pollution build-up.
• These conditions are consistent with low wind speed measurements and high pressures
• Elevated CO2 mixing ratio recorded across London (airport and city) with over 100 ppm rise at the peak of the anticyclone
(9th & 10th August)
• Apart from the local emissions, a rise in baseline of CO (~200 ppb) was observed during these conditions, hence risk of
exposure to elevated pollution mixing ratios than under well mixed conditions.
References
1. Mead, M.I., Popoola, O.A.M., Stewart, G.B., Landshoff, P., Calleja, M., Hayes, M., Baldovi, J.J. , Hodgson, T., McLeod, M., Dicks, J.,Lewis, A., Cohen, J., Baron, R., Saffell, J., Jones, R L. , The use of electrochemical sensors for monitoring urban air quality in low-cost, high-density networks. Atmospheric
Environment, 2013. 70: p. 186-203.
2. David Carslaw and Karl Ropkins (2012). openair: Open-source tools for the analysis of air pollution data. R package version 0.7-0.
3. Heathrow and London City flights disrupted by fog (2 March, 2012) . BBC News London. Retrieved from http://www.bbc.co.uk/news/uk-england-london-20039145
Acknowledgements
S. Thomas and D.Vowles (BAA), NERC for PhD studentship, NERC: High
density network system for air quality studies at Heathrow airport (funded
Oct., 2010)