local authority case study large scale deployment of...

Local Authority Case Study – Large Scale

Deployment of Sensors

D. Carruthers1, D. Clarke2, K. J. Dicks3, R. A. Freshwater4, M. Jackson1,

R. L. Jones4, C. Lad1, I. Leslie5, A. J. Lewis3, H. Lloyd4, O. A. M. Popoola4,

A. Randle6, S. Ulrich4

1Cambridge Environmental Research Consultants, UK 2Cambridgeshire County Council, Cambridge, UK3Cambridge City Council, Cambridge, UK4Department of Chemistry, University of Cambridge, UK5Computer Laboratory, University of Cambridge, UK6Environmental Instruments Ltd., Stratford-upon-Avon, UK

AQE 2017, Telford, 25th May 2017 1

AQE 2017, Telford, 25th May 2017

Talk outline

• Premise of inter-comparison

• AQMesh, network deployment

• Comparison with reference instruments

• What can we do with the measurements?

- Model comparison

- Source attribution• Local emissions

• Long range sources

2

AQE 2017, Telford, 25th May 2017

Premise of inter-comparison:

• Test of ‘out of box’ AQMesh performance

• No local calibration/re-scaling

• No pan-network analysis (individual sensors)

• NO, NO2, PM2.5, PM10 only (determined by

available reference instruments)

3

Sensor Calibration Gas sensors

Comparison between Alphasense electrochemical

sensors and local (to AQMesh) reference

instrumentation to determine sensor specific calibration

parameters.

Particle sensor

OPCs co-located with a “gold standard pod” at the

AQMesh outdoor test facility to provide consistent

calibration parameters.

AQE 2017, Telford, 25th May 2017 4

CO, NO, NO2, O3, SO2,

PM1, PM2.5 and PM10

Cross network NO2 performance

(pre-deployment)

Gradients = 0.94 ± 0.07

R2 = 0.8 ± 0.11

Intercepts = 0.34 ± 0.47ppb

AQE 2017, Telford, 25th May 2017 5

Sensor-sensor

comparisons

Cross network PM2.5 performance

(pre-deployment)

Gradients = 0.98 ± 0.07

R^2 = 0.98 ± 0.17

Intercept=0.13 ± 0.3ug/m3

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Sensor-sensor

comparisons

AQE 2017, Telford, 25th May 2017 7

Cambridge deployment (20 nodes)

Northwest Cambridge(building development)

Central Cambridge(high traffic density)

South Cambridge(biomedical campus development)

Reference site(Gonville Place)

AQE 2017, Telford, 25th May 2017 8

NO2 city centre comparison (pre-ratified)

Gradient Intercept R2

0.55 (0.006) 10.0 (0.1) 0.50

• Similar features (diurnal

signatures) in both

• AQMesh significantly higher

in absolute amounts than

reference (not consistently)

AQE 2017, Telford, 25th May 2017 9

NO2 city centre comparison (pre-ratified)

Gradient Intercept R2

0.75 (0.01) 4.5 (0.2) 0.64

1.67 (0.02) 6.1 (0.16) 0.64

0.67 (0.007) 4.9 (0.19) 0.78

• Clear calibration changes

(three distinct phases) (in

which instrument……?)

AQE 2017, Telford, 25th May 2017 10

NO2 city centre comparison (ratified)

No reference data!

NO2 Gradient Intercept R2

pre 0.55 (0.01) 10.0 (0.1) 0.50

post 0.82 (0.01) 5.1 (0.13) 0.74*

*Improvement is from AURN ratification

NO Gradient Intercept R2

pre 0.85 (0.01) 4.4 (0.21) 0.49

post 0.87 (0.01) 0.63 (0.3) 0.65*

AQE 2017, Telford, 25th May 2017 11

PM2.5 city centre comparison (ratified)

• PM events captured

• Some overestimation by AQMesh

• Little/no difference on ratification

Gradient Intercept R2

pre 0.92 (0.01) -3.0 (0.15) 0.41

post 0.92 (0.01) -3.0 (0.15) 0.42

AQE 2017, Telford, 25th May 2017 12

PM10 city centre comparison (ratified)

• PM events captured by AQMesh

• Magnitudes significantly

overestimated in AQMesh

• Little/no difference on ratification

Gradient Intercept R2

pre 1.17 (0.02) -8.7 (0.51) 0.21

post 1.17 (0.02) -8.7 (0.51) 0.21

Gonville Place AQMesh reference

comparison statistics summary

Gradient Intercept R2

NO2 pre 1.07 (0.01) 10.0 (0.1) 0.50

NO pre 1.07 (0.01) 4.4 (0.21) 0.49

PM2.5 pre 0.92 (0.01) -3.0 (0.15) 0.41

PM10 pre 1.17 (0.02) -8.7 (0.51) 0.21

AQE 2017, Telford, 25th May 2017 13

Gradient Intercept R2

NO2 post 0.82 (0.01) 5.1 (0.13) 0.74

NO post 1.09 (0.01) 0.63 (0.27) 0.65

PM2.5 post 0.92 (0.01) -3.0 (0.15) 0.42

PM10 post 1.17 (0.02) -8.7 (0.51) 0.21

Pre- AURN ratification

Post- AURN ratification

Improvement is from AURN ratification

AQE 2017, Telford, 25th May 2017 14

NO2 city centre model-AQMesh

comparisons

Gradient R2

AQMesh - ADMS 0.34 0.24

AQMesh - reference 0.82 0.74

• Model captures broad behaviour

• Poorer R2 c.f. AQMesh-reference

• Poorer model-reference R2

AQE 2017, Telford, 25th May 2017 15

PM2.5 city centre model-AQMesh

comparisons

Gradient R2

AQMesh - ADMS 0.265 0.03

AQMesh - reference 0.92 0.42

• Model captures magnitudes of

events but not timing…..

• Significantly poorer R2 c.f. AQMesh -

reference

AQE 2017, Telford, 25th May 2017 16

Average NOx model-AQMesh comparisons

– all stations

• Model ~ captures AQMesh spatial gradients

• Local (spatially heterogeneous) sources

AQE 2017, Telford, 25th May 2017 17

Average PM model-AQMesh comparisons

– all stations

• Model ~ captures (lack of) spatial gradients

• Averages dominated by non-local sources

AQE 2017, Telford, 25th May 2017 18

What does this mean?

Spatial gradient implies local

source in city…..

Local intervention possible

No spatial gradient implies

mainly regional source…..

Regional intervention

required

Polar bivariate plots (© OpenAir!): source

apportionment

19AQE 2017, Telford, 25th May 2017

NO2: significant differences– road sources (1)– local sources (2)– non local sources (3)

1

1

1

2

3

3

3

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3

3

3

PM10: broadly similar – longer range transport?– building site influences (1)

1

11

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AQE 2017, Telford, 25th May 2017 22

Summary

• AQMesh sensor performance ‘out of box’ performance:• Sensor- sensor reproducibility very good.

• NO/NO2/NOx inter-comparison with ratified measurements good.

• PM measurements capture events, some overestimation (esp. PM10).

• Ratification process produces some rather surprising results……

• AQMesh captures spatial gradients well• Spatial gradients for NOx (local emissions)

• Little spatial gradients for PM (long range transport)

Important for understanding role of policy interventions

• Source attribution

- Hotspot detection

- NO2 short term exceedences

- PM emissions building works

AQMesh performs well: hotspots, A/Q monitoring/control

D. Carruthers1, D. Clarke2, K. J. Dicks3, R. A. Freshwater4, M. Jackson1,

R. L. Jones4, C. Lad1, I. Leslie5, A. J. Lewis3, H. Lloyd4, O. A. M. Popoola4,

A. Randle6, J. Stocker1, T. Townend6, S. Ulrich4

1Cambridge Environmental Research Consultants, UK 2Cambridgeshire County Council, Cambridge, UK3Cambridge City Council, Cambridge, UK4Department of Chemistry, University of Cambridge, UK5Computer Laboratory, University of Cambridge, UK6Environmental Instruments Ltd., Stratford-upon-Avon, UK

AQE 2017, Telford, 25th May 2017 23