Air Monitoring
Key: 1 Teddington 2 Hackney 3 Poplar 4 Detling
Olympic Park
from local sources at low wind speeds dominated. There was poor dispersion of locally generated CO2
conditions. Poplar CO2
under these
27
Hackney CO2
Sensors were first characterised in the laboratory for their linear response and stability, so the uncertainty of the final measurement could be quoted. The measurements and instrument diagnostics were continuously sent to the control centre. This helped to ensure that the equipment was operating correctly and the immediate availability of carbon dioxide concentrations.
Measurements began in June and finished at the end of September and the results are shown below in the context of the three questions stated above.
1.How do concentrations of carbon dioxide and methane vary between rural, Outer London and London Centre sites?
An increase in average concentrations over the measurement period was seen for all species between the rural site at Detling and the Outer London site in Teddington.
The average increase was 7.2 ppm for CO2 . There was a further
increase in average concentrations between Teddington and the average of the Inner London sites of 1.04 ppm. The red line in the graph below shows the baseline CO2
concentration
for 2011 for the UK of 395 ppm, according to Met. Office and DECC measurements.
It is difficult to make a comment about the magnitude of concentration increases but they are in line for that seen from other pollutants e.g. Nitric Oxide (NO) from combustion processes. This increase was due to emissions from local traffic and fossil fuel fired heating.
2.How do meteorological conditions impact on these measured concentrations?
The variation in the concentrations of CO2 , with wind speed
and direction, are best understood from polar plots, where the colour represents the measured concentration at a specific wind direction and speed. The distance from the centre of the plot corresponds to wind speed, i.e. colours close to the origin are concentrations measured at very low wind speeds whilst colours further from the origin represent concentrations measured at higher wind speeds.
The angular position represents the wind direction. The white areas represent wind directions and speeds that did not occur due to the short nature of the measurement campaign (3 months).
Teddington CO2 Teddington’s high levels of CO2
expected from the NE if CO2 (red and yellow) were to be from London was the main source detected. Raised concentrations in the middle suggest CO2
At Detling, high levels (red and yellow) were expected in the NW if CO2
from London is the main source detected. We
observed raised concentrations from the NNE, likely to be from Kingsnorth Power Station.
Detling CO2
Raised concentrations in the middle of the plot for Poplar and Hackney suggested that CO2
from local sources at low wind
speeds dominated the measurements. Higher concentrations from the SE at Poplar were believed to be from traffic from the Blackwall Tunnel.
One thing the results showed us was that concentrations were affected by wind conditions. At times of low wind speed, the concentrations were higher as a result of poorer dispersion of local emissions. Concentrations as high as 520 ppm CO2
were
seen at Teddington, Poplar and Hackney compared with the average peak in the daily value of 412ppm to 424ppm. The dominance of local sources was expected as the measurements were taken at the relatively low heights of 10-15m.
3.How do expected concentrations from known sources compare with the measured concentrations for this period?
The average variation in measured CO2 concentration during
a day is shown for each site below; the y-axis the shaded area represents the uncertainty in the mean y-value due to the standard deviation of the results over that averaging
www.envirotech-online.com IET March / April 2014
Page 1 |
Page 2 |
Page 3 |
Page 4 |
Page 5 |
Page 6 |
Page 7 |
Page 8 |
Page 9 |
Page 10 |
Page 11 |
Page 12 |
Page 13 |
Page 14 |
Page 15 |
Page 16 |
Page 17 |
Page 18 |
Page 19 |
Page 20 |
Page 21 |
Page 22 |
Page 23 |
Page 24 |
Page 25 |
Page 26 |
Page 27 |
Page 28 |
Page 29 |
Page 30 |
Page 31 |
Page 32 |
Page 33 |
Page 34 |
Page 35 |
Page 36 |
Page 37 |
Page 38 |
Page 39 |
Page 40 |
Page 41 |
Page 42 |
Page 43 |
Page 44 |
Page 45 |
Page 46 |
Page 47 |
Page 48 |
Page 49 |
Page 50 |
Page 51 |
Page 52 |
Page 53 |
Page 54 |
Page 55 |
Page 56 |
Page 57 |
Page 58 |
Page 59 |
Page 60 |
Page 61 |
Page 62 |
Page 63 |
Page 64 |
Page 65 |
Page 66 |
Page 67 |
Page 68 |
Page 69 |
Page 70 |
Page 71 |
Page 72 |
Page 73 |
Page 74 |
Page 75 |
Page 76
