To what extent do car emissions affect NO2 levels across Leicestershire and how can it be reduced?
The project focuses on analysing the dispersion of NO2 exhaust emission in a range of different environments in Leicestershire (altitude/ rural/ urban) by using MOS sensors to construct a map of the pollution trail on Google Earth. The project consisted of 3 separate experiments with an underlying goal at the end:
A Zephyr was deployed on a hot air balloon and the pollution and the measurements of NO2 was recorded. It was found that NO2 diffused through the air at a constant rate once wind interference was removed. The dilution factor with respect to height was calculated to be 0.0215
Figure 6: a) Dispersion of NO2 during balloon flight on the 2nd of November b) Visualisation of possible cities that could have contributed to the recorded NO2 concentrations
The research conducted by D. Baumer et al. recorded the dispersion of vehicle pollution while under the influence of induced motorway turbulence to reach heights of up to 60 m therefore there were initial fears of monitoring minimal deviation in NO2 concentrations at high altitudes (over 600 m). The concerns were quickly dissipated as the pollution trial projected in Figure 6 a shows an excellent deviation in concentration along the path.
At the launch site, significant amount of NO2 pollution was detected. A possible explanation of the high levels could be due to a sudden change in temperature, for example transferring the sensor from a closed system (car) out to the open. This would alter the temperature recorded drastically and as seen in the calibration equation 15, temperature plays a critical role in determining the concentration levels of NO2.
The concentration throughout the day remained high, even at altitude, and this suggested that the pollution on the day itself must have just been high. This is a more plausible explanation than the sudden temperature change as the sensor wasn’t in a complete closed off system as the window of the car was left open. The theory was further looked into by analysing the concentration levels monitored from the AURN stations in several cities on the day of the flight experiment.
The hot air balloon followed a near perfect straight line trajectory in the south-east direction for approximately 45 minutes. Extrapolating the trail back determined possible cities that could have contributed to the high NO2 levels at the launch site which is highlighted in Figure 6 b. NOx is classified as a species with a moderately long lived lifespan and in the troposphere the average life time is estimated to be around a day . Specific life time is difficult to determine as it strongly dependant on the atmospheric conditions which is constantly changing. Extrapolating the flight path revealed that Birmingham, Leicester and Stoke-On-Trent (air distance of 38, 22 and 67 miles respectively from the launch site) are in the average wind direction, as presented in Figure 6 b. The wind speed on the 2nd of November 2016 was 8 mph. If we assume the NO2 plume was transported at the same constant wind speed in the straight-line trajectory for the entire duration, the NO2 from the three cities would reach the launch site in approximately 4.25, 2.75 and 8.38 hours respectively. The duration is short enough to make Birmingham, Leicester and Stoke-on-Trent as possible NO2 sources that contributed to the pollution levels observed in the flight. To further support the theory, the Defra data shown in Table 1 portrays extremely high NO2 concentrations on the 2nd of November 2016.
Table 1: NO2 concentrations monitored from the AURN stations in Birmingham, Leicester and Stoke-On-Trent on the 2nd of November 2016.
The hot air balloon experiment was conducted between 2-3 pm. The early morning pollution times in Table 1 were determined by subtracting the previously estimated NO2 durations from when the hot air balloon experiment was carried out.
The data presented in Table 1 show extraordinary amount of NO2 being released from the cities. The highest concentration recorded in each of the cities were 92 μg/m3 direct NO2 and 269 μg/m3 NOx as NO2 from Birmingham, 94 μg/m3 direct NO2 and 444 μg/m3 NOx as NO2 from Leicester and 126 μg/m3 direct NO2 and 574 μg/m3 NOx as NO2 from Stoke-On-Strent. These concentrations are well above the expected 40 μg/m3 the EU is demanding from the UK. The flow of pollution can also be visualised by comparing the emitted NO2 concentrations from Table 1 with the relative distance the cities are from each other in Figure 6 b. Highest NO2 concentration was observed in Stoke-On-Trent, the pollution would have follow the direction of the wind via advection towards Birmingham and Leicester. Both cities are at a similar distance from Stoke-One-Trent and this could be reflected from the similar concentrations monitored between Birmingham and Leicester.
The high volumes of NO2 emissions from the 3 cities explains why enhance pollution levels were observed during the flight.
Figure 8: Variation of NO2 concentration during hot air balloon launch
The flight path is broken down into segments, focusing on areas where variation was noticed as the trail developed. Figure 8 shows the deviation of NO2 concentration during launch. The colour changed from grey to red indicates a change in NO2 concentration. The grey is not illustrated on the colour bar in Figure 6 as it exceeds the general trend limit which is determined from the average pollutions concentration presented in the overall data. The concentration shift was expected as the NO2 would have diffused from an area of high concentration to an area of low concentration, which would be found in higher altitudes. As the balloon reached higher altitudes the colour shifted from red to orange, yellow and eventually green. The colour scheme was followed down the colour bar (right to left) which signified the gradual decline in NO2 levels. The mobile app Trials was used in case the GPS on the sensor failed. Although the sensor GPS worked perfectly, the app provided quantitative altitude measurements which was used to determine the dilution of NO2 in the air with respect to altitude.
Graph 5: Plot of [NO2] against Altitude, measurements taken from hot air balloon between 14:38 – 14:41 on 2nd of November 2016
Although the hot air balloon generally increased in altitude, there was some fluctuation at the beginning of the flight. Graph 5 was plotted between the period when a steady rise was recorded. The graph shows a negative correlation between altitude and NO2 concentrations, where a decline in NO2 was recorded with increasing altitude. The correlation between NO2 dispersion and altitude has a very linear relationship and this is reflected from the 0.9993 R2 value of the trendline, where 1 equals direct relationship.
Between 472 and 704 metres, the concentration difference of NO2 was 5 μg/m3 . Using this data, the dilution factor of NO2 can be calculated with respect to distance. Equation  shows the dilution factor of NO2 when it ascended 232 meters in the air:
dilution factor= ∆[NO2]∆Distance=5232=0.0215 ug/ m4
It should be noted that the measurement at different altitudes were not taken at a fixed x (horizontal) position as illustrated in Figure 9. Due to the movement of the air the balloon was pushed further along the x direction. However, the NO2 diffusing upwards would also experience an equal horizontal force exerted from the wind in the same direction so the effect of the horizontal dilution can be ignored. A more accurate and reliable vertical profile (varying altitude) of NO2 diffusion was obtained as the direction of the plume is followed in the balloon. This would also mean that the same plume was being monitored without there being any interference with a secondary plume. In a fixed position (single x point) scenario, at least two sensors at different heights (z axis) would be required to construct a vertical profile however the wind would introduce several plumes and this would provide unreliable measurements.
Figure 9: Illustration of plume and hot air balloon (x1,2,3) movement
Notice that the dilution factor with respect to distance can also be more accurately determined from the gradient of the Graph 5. From the equation generated from the graph, the y-intercept (therefore ground level pollution) is predicted to be around 71 μg/m3 . From Figure 8 it can be observed that the predicted ground level concentration from Graph 5 was near the experimental value (67 μg/m3 ) which further supports the linear relationship between altitude and dispersion levels.
Figure 10 a shows a sudden increase in NO2 concentration when the balloon flew over the A508. The change in concentration is due to the emissions released from cars. Closer to the ground level this spike would be expected but it was surprising to see the how the concentration was effected at an altitude of 759 meters, especially when the wind was blowing in the south east direction. This increase in concentration directly above the A508 reveals that NO2 must have dispersed up through the air at a fast rate. When the gases are initially emitted from the exhaust, the pollutant gas would be at a much higher temperature than the surrounding air. The hot exhaust would quickly expand and rise upwards. High speeds can be reached by vehicles on the A508, meaning the engine would be working even harder when compared to engine temperatures during city driving. Hot exhaust emissions would accelerate vertically upwards at as the expanded gas will have less density than the cooler surrounding air and will experience an upward buoyancy force from the surrounding cooler air. The larger the temperature difference, the faster the molecules will rise through the air. A study by M. Ghazikhani et al reported that a petrol car with an engine speed of 4500 RPM had exhaust temperature of 305 oC . Therefore, the convection is thought to be involved in the fast vertical dispersion. However, in the real world the heat/energy of the gases will dissipate drastically as soon as it leaves the exhaust pipe.
Figure 10: The contrast between the dispersion of exhaust plume due to induced vertically turbulence (red: with turbulence, Blue: without turbulence)
The work conducted by N. Kathoff et al and D. Baumer et al also gave rise to another plausible explanation on the observation. In comparison to the literature reviews, the main parameter of the wind flowing at a perpendicular angle to the motorway was met in this experiment. Their studies suggested that motorway induced vertical turbulence that can be experienced up to 60 m in the air. As wind (advection) is the general method of pollution transportation, the vertical wind would have propelled the NO2 into the air and caused it to disperse at a faster rate. As a visual aid, Figure 10 shows how the vehicle emissions are dispersed on the motorway in red. The combination of convection, advection and diffusion would have enhanced the initial upwards dispersion of NO2.
Figure 11: a) Variation of NO2 concentration before and after A508 at an altitude of 759 m.
b) The angle the hot air balloon intercepted A508 and the angle of exit
However, the hot air balloon flew over A508 over 700 m in the air. The hot exhaust and vertically induced turbulence is not enough to explain the sudden jump right in concentration right above the motorway as the natural wind would have carried the pollution away from the motorway. N. Kathoff et al also noted that the movement of vehicles can generate turbulence that will flow parallel to the motorway. This suggests that the pollution could have been released further upstream on the motorway and experienced vertical and horizontal forces previously discussed would have guided the plume diagonally up towards the hot air balloon.
Interestingly, the direction of the balloon also altered noticeably when it flew across the motorway. Figure 11 b illustrates the balloon diverted from the expected direction by 20 o once crossing the motorway’s threshold. Although it is unlikely, the results suggest that the change in direction could be a result from the induced turbulence flowing alongside the motorway. If this were to be the case, the vehicle induced turbulence has a much greater effect from what previous studies has recorded. Their experimental set up consisted of deploying sensors at a height of 50-60 m which could have limited the observed effect of the generated turbulence.
The experiment provided conflicting results from previous studies and it would have to be repeated with the same conditions (wind speed/direction and volume of traffic) to rule out coincidences.
Figure 12: Variation of NO2 concentration across Pitsford Reservoir at 460-500 m altitude
As the experiment continued, this time a dip in concentration drew attention. When the balloon flew over the reservoir, the concentration of NO2 decreased from 56 μg/m3 to 50 μg/m3 . The drop indicated chemical reaction occurring over the reservoir to cause the depletion of NO2.
M. Garold et al. state that NO2 hitting the surface of the water will become trapped between the air/water interface, where it can be held long enough for the molecule to interact with a second NO2 molecule to produce HONO. HONO rapidly photolyze in the air to OH radicals which can cause further destruction to NO2 in the air via reaction11. It should be noted that the paper conducted the research via molecular dynamic models. No actual experiment was carried out to provide evidence of this theory. Thereby the decline in NO2 concentration across the reservoir in this experiment support the theory of trapping NO2 molecules. The paper also mentioned that clean water will enable NO2 to adsorb more efficiently onto the surface of the water by over 10-fold. As the reservoir consists of pure water, there is a much greater probability for the NO2 molecule to be trapped on the surface of the water for a longer duration, thus increasing the chance for an interaction with another NO2 molecule to form HONO species. The surface area of the reservoir was determined to be 691 022 m2 from Google Earth. The large surface area of the reservoir would also ensure more NO2 molecules to adsorb onto the air/water interface, thereby naturally keeping NO2 out of the atmosphere. The efficiency of the clean water can be seen in the rapid decline in NO2 levels.
It can’t be ignored that the lower concentrations may also be due to there being no NO2 emissions in the area as water does not release NO2. The sudden change in NO2 concentration can simply be due to flying over a region of area there is no production of NO2, in comparison to flying over vegetation that is known to exhale some NO2.
Towards the end of the experiment the balloon drifted across another polluted road (A43). This road also has similar motorway properties as vehicles travel on the A43 at high speeds, therefore harder working engine releases greater amount of NO2 into the atmosphere.
Once again the balloon cut across the motorway at a perpendicular angle, meaning the wind must have been also applied at a 90 degree angle to the motorway, making the studies conducted by D. Baumer et al and N. Kalthoff applicable to this scenario. Yet again there has been a spike in concentration directly above the A43. The increase in concentration across two different motorways validates the initial observation and proves it was no anomaly. There is a larger initial jump in concentration on the A43 than A508. This is due to the balloon flying over the A43 at a lower altitude therefore it was closer to the source of NO2 production, resulting in less NO2 dilution. The experiment proves how severely the motorway pollution effect concentration levels at altitude.
At landing NO2 concentrations were expected to increase due to greater pressure at lower altitudes. This was not the case, during landing the concentration of NO2 declined from 58 μg/m3 to 53 μg/m3 . One possible explanation can be due to higher temperatures at lower altitudes. Higher temperatures provide more kinetic energy to the molecules therefore NO2 moles would move around and diffuse at a faster rate, lowering the concentration. However, this should not be enough to lower the concentration as NO2 sources are locatedat ground level. Stronger winds could have also picked up, thereby dispersing NO2 more.
Figure 14: Variation of NO2 concentration during landing
Figure 15: Overall NO2 concentration comparison of rural (Bradgate park walk) and urban (Leicester city drive) on 7th of November 2016
Graph 6: Average NO2 comparison between rural (Bradgate Park) and urban (Leicester City) on 7th of November 2016
The difference between rural and urban regions are apparent in Figure 15. As shown in the colour bar on the bottom left corner of the diagram, dark blue/purple is at the lower end of the colour spectrum representing concentrations between 40-46 μg/m3 . The dark blue/purple regions are projected in the rural region of the map (top left) and in the heart of Leicester city the trail turns red which is at the opposite end of the colour bar. Graph 6 shows the plot of concentrations presented in Figure 15 against time. The red dashed line divides the rural and urban readings. The average concentrations of the rural and urban areas were determined to be 44 and 62 μg/m3 respectively. The sharp increase in concentration at 14:20 pm were omitted as it was due to the car park which did not portray actual readings of Bradgate Park. Graph 6 emphasises that people living in urban areas are more at health risk from high NO2 pollution. The results showed that urban regions are approx. 41 % more polluted with NO2 when compared against rural regions. This significant increase is due to the city being more populated with vehicles which emit vast amounts of pollution. The experiment is in support of D. Krochmal et al. and underlines the major health risks posed by high levels of NO2 in cities. The averaged experimental NO2 concentration of 62 μg/m3 is well above Europe’s expected 40 μg/m3. Leicester requires to make some drastic changes to match the limit demanded by Europe.
Figure 16: a) Variation of NO2 concentrations at rural Bradgate park, b) variation of altitude across Bradgate park, c) graph comparing NO2 concentration against altitude at Bradgate park
Once again, the trail is broken down for a closer inspection on the factors effecting NO2 concentrations. The lowest NO2 reading was recorded right beside the Cropston Reservoir. The readings varied between 41-45 μg/m3 along the side of the reservoir and creating a distance resulted in the concentration levels to reach up to 48 μg/m3. This shows the effect the reservoir has on the nearby NO2 concentration levels. The decline in NO2 near the reservoir can again be due to lack of NO2 sources in the area. Water does not produce NO2 and since the reservoir has a very large surface area of 338,142 m2 , it is not surprising to measure a decrease in NO2 levels in the nearby vicinity. The surface area is more than halved in comparison to the reservoir encountered during the hot air balloon experiment, nonetheless the NO2 levels have still been depleted more than enough for the Zephyr to detect. Further work could explore the effect the Cropston reservoir has on NO2 concentrations with the involvement of a sonic anemometer. For example, if the wind was blowing towards reservoir from the direction of the path, these results would neglect the influence of the reservoir. If the wind was blowing in the opposite direction, this would include the effect the reservoir has on NO2 concentrations. Comparing these two set of data would confirm the direct involvement of the reservoir on NO2 levels in the area. Another method would require multiple Zephyr sensors deployed in a straight line away from the reservoir, each being 10 m apart from each other and monitor the difference in NO2 concentrations between the sensors.
The decline in NO2 levels was similarly observed during the hot air balloon experiment proving that the reduction in concentration is of no coincidence and the interaction between NO2 and the water surface is likely to be occurring.
An unexpected drop in concentration was detected where the colour switched from blue to purple, the colours represent concentrations around 50 and 40 μg/m3 respectively. At first the reason behind for sudden change in concentration was unknown until the concentration was compared against altitude measurements which were taken with the Trials app. In Figure 16 A the number 3 (where the NO2 shift occurs) represents the highest altitude reached on the map, at 175 m. This is also where the lowest concentration of NO2 was observed. To make analysis diagrammatically clearer, numbers (1 – 5) were placed on the map to show where the specific measurements were used to plot Figure 16 C. The graph clearly indicates negative correlation between altitude and NO2 concentration, where an increase in altitude decreases NO2 concentrations (points 1-3). Between points 3-5 the drop-in altitude caused a surge in NO2 levels. The gradient generated from concentration against altitude plot is not as smooth in comparison to Graph 5. This is due to wind interference affecting NO2 levels. As explained earlier with the help of Figure 9, the hot air balloon and NO2 plume moved at the same horizontal rate as the wind carried them both .
Figure 17: Variation of [NO2] at Bradgate carpark
After the Bradgate loop was complete the sensor was carried back to the car. In the car park the NO2 levels shot up to 67 μg/m3 from 47 μg/m3 . The car park contained a high volume of vehicles. Vehicles emit considerable amount of NO2 and NOx to the nearby surroundings which must have been picked up by the Zephyr. As the car park is in open space, this dramatic increase in concentration (
∆20 μg/m3) was not expected. The observation from this experiment can be used to investigate the amount of pollution generated by open spaced car parks in comparison to closed.
Figure 18: Variation of NO2 concentrations when driven near the Cropston Reservoir
During the drive back towards Leicester city, the route consisted of driving past the Cropston Reservoir. Once more the close surroundings near the reservoir have lowered NO2 concentrations. The of NO2 depletion near reservoirs is becoming a common theme. There is an 18.5% reduction towards the centre of the reservoir. Figures 16 & 18 show that vast surface areas of water are just as effective at lowering NO2 concentrations as much as altitude is. The results indicate that the air quality in Leicester city can be improved by incorporating large water surfaces in to the city.
Figure 19: A) Variation of NO2 concentrations when driven through Leicester city centre,
B) Variation of NO2 concentrations when driven on Welford road
Figure 19 A reflect the concentration levels on the 7th of November 2016 in the centre of Leicester city. The city centre reached NO2 concentrations of up to 69 μg/m3. Near the AURN station located at University of Leicester, the Zephyr gave a reading of 65 μg/m3 at14:41 pm. The AURN monitoring site gave 41 μg/m3 as direct NO2 and 66 μg/m3 NOx as NO2 at 15:00 pm . The discrepancies between the two monitoring sites can be a result of the AURN station providing an hourly average concentration whereas the Zephyr provides specific measurements every 10 seconds. The Zephyr was also exposed to direct NO2 from the exhaust fumes with minimum NO2 diffusion as measurements were taken on the road. The AURN station is at a distance of 121 m from the point where the Zephyr took the measurement (Welford road). The concentration near the AURN monitoring site is dependent on the busy Welford road and the emitted NO2 molecules would have to diffuse 121 m through the air in order to react the monitoring site. This explains the lower concentration detected by the AURN station.
As shown in Figure 19 B, NO2 levels became more concentrated further down Welford road. The time (around 14:41 pm) played a crucial role for the high concentration levels, which were due to traffic caused by parents picking children up from school. The red trail is a very good indication of where the congestion was at its worst. The visualisation on the map shows this was right before the traffic lights. The high concentration levels right before the traffic lights raised questions to what extent the traffic lights played in polluting the surrounding area with NO2. This is later explored in a separate experiment. The red pollution trail can also be used to describe the length of the congestion, which was calculated at 322 m (measuring length across the map where high concentration was detected). An average family’s car is around 3.67 m in length. A rough estimation of 88 cars occupied the congested red zone, assuming no spaces were left in-between cars and only one lane was taken into account. This can be used to determine a rough estimation the number of cars it would take to create such a polluted zone. Figure 19 B empathises the invisible dangers of walking beside congested roads. Children and old people should especially try to avoid walking or standing beside congested area as pollution levels can reach to concentrations as high as 79 μg/m3, which is categorised as moderately dangerous NO2 concentrations and individuals who are sensitive to NO2 should avoid long term exposure .
Figure 20: Variation of NO2 concentrations due to traffic lights around University of Leicester
The previous experiment highlighted the surge in NO2 concentrations near traffic lights. From that a further study was conducted to visualise the extent of NO2 pollution generated around traffic lights. Figure 20 expose all the traffic lights around University of Leicester. Region A, immediately supported the results collected from the rural/urban experiment. Right before the traffic light the concentration levels were 73 μg/m3. The concentration dropped to 71 μg/m3 when the sensor was carried past the traffic light.
The next pair of traffic lights in region B provided more interesting results due to the complexity of the connecting 3 roads. A relatively high concentration of 74 μg/m3 was monitored for 30 seconds before the traffic lights were approached. Cars were noted to be parked behind the traffic lights which is why 74 μg/m3 was monitored for a while. After the traffic light threshold was crossed, the concentration plummeted to 71 μg/m3. The change of 3 μg/m3 is too large for it to be due to the distance created from the traffic light alone at walking pace. A plausible theory is that the cars must have become mobile and the movement created a small turbulence that caused the nearby air (containing NO2) to disperse, resulting in lower concentrations. Therefore, the rapid change in concentration can also be used to provide an estimation to when lights switched green. Natural wind could have also blown in from the opposite direction with respect to walking direction but no wind sensor was deployed in this experiment.
The experiment confirmed that vehicles are a very dominating pollution source, however it has also proven to be a good way of dispersing (within proximity) pollution due to the induced turbulence. The study also warned that static cars provided a much higher health risk from NO2.
Very high NO2 concentrations were picked up at the next set of traffic lights in region C. A staggering 78 μg/m3 was recorded near the area. The high concentrations were a product of the congestion created by the traffic lights which was further enhanced by the busy roundabout which introduced more cars to the area.
Graph 7: Illustrating the relationship between NO2 and O3 against time in region C
Graph 8: Plot of [O3] vs [NO2] in region C
Graph 8: Describes the relationship between NO2 and O3 in region C. Concentration against time was also plotted for both set of pollutants. The blue data set (NO2) shows a very linear relationship with time (time can also be thought as distance) when approaching the traffic light, up until 17:12 pm. The linear relationship can be a result of the vehicles being in a fixed position, and direct vehicles emissions being recorded. From Figure 20, the most NO2 polluted point in region C can be identified exactly where the traffic lights are positioned. The data shows that traffic lights act as NO2 emission sources. A person is more likely to be exposed to the higher volumes of NO2 when standing within close proximity to traffics. Beyond the traffic lights (17:12 pm) NO2 concentration fell less linearly. The dilution represents getting further away from the emission source. On this side of the traffic lights there are no/ fewer cars so the fluctuation describes the diffusion rate of the NO2.
So far only direct NO2 emissions have been considered. Graphs 7 & 8 broadcasts how the O3 level is affected in region C. The graphs also remind that primary NO2 emissions is not the only concern that needs to be thought about. The NO2 and O3 molecules mirror each and this illustrates that reaction4 is taking place, where NO from the exhaust rapidly reacts with present O3 to form NO2. Graph 7 shows that as more ozone is used up, more NO2 is generated therefore NO should also be treated as NO2 due to the rapid conversion. This is very concerning as background researched showed that a much greater percentage of NO than NO2 is released from vehicles.
Providing separate measurements for NO and NO2 is another good method for car manufacturers to further conceal the amount of NO2 vehicles are responsible.
The concentration of NO2 increases towards the end of the data. This is due to the influence of the next set of traffic lights. However, no sharp increase on NO2 concentration was detected and the plume trail stays at the same colour therefore it is assumed that the traffic lights were green, further proving that designing a better traffic light system to optimise traffic flow is beneficial for NO2 dilution as well as pollution data can be used to describe traffic light activity.
Following the A6 towards the trains station showed very similar results to the previously discussed traffic light. The majority of the A6 was highlighted in yellow/orange/red which represents high concentrations of NO2. The study proves the number of traffic lights on a stretch of road directly relates to the amount of NO2 released in the area. In comparison to the road containing less traffic lights between segment A and C, the A6 is significantly more polluted and the traffic lights are the cause of the problem. The most NO2 polluted region was monitored at 81 μg/m3 next to the train station at 17:24 pm. The train timetable was retrieved from Raildar  for the date 26/01/2017, and the train activity at Leicester train station around 17:24 pm was investigated..
|Lei Arrival||Origin||Destination||Lei Departure|
|17:14||17:13½||Birmingham New Street||Stansted Airport||17:18||17:18|
|Leicester||Birmingham New Street||17:18||17:18|
|17:24||17:24||Sheffield||London St. Pancras||17:24||17:26|
|17:24||17:24||London St. Pancras||Nottingham||17:25||17:26|
Table 2: The train timetable for Leicester train station on the 26/01/2017 between the time 17:14-17:26 pm
Table 4 shows 6 trains had gone through Leicester city train station within the timeframe that would have affected the experimental concentrations of NO2. Trains are known to release significant amounts of pollution. A study conducted by G.Fuller et al. show that trains can increase NO2 levels by 36 μg/m3 in comparison to the background reading that was located 600m away from the train station . They also included that rail source of NOx is 25 % more than Marylebone Road  and this makes train stations of great concern as Marylebone road is known to be one of London’s most polluted street.
Across the train station, following the road down the A594 the concentration levels remain high. The exhaust emissions from the trains in table 4 can still influence the amount of NO2 along the A594 because the train tracks run right beside it. Significantly high concentrations are observed between the two traffic lights in region D. It appears like the two traffic lights have trapped vehicles between them, causing high emissions of gases to pollute the area. The same observation is made with the next pair of traffic lights where there is a high concentration between them compared to the surrounding area. This shows that if two sets of traffic lights are close enough to each other, their pollution combines and merges into one, creating denser pollution.
Overall, traffic lights are primarily used to enable safe movement of cars and prevent collisions. Essentially to make roads safer for both pedestrians crossing the road and vehicle users. However, this study suggests the excessive use of traffic lights is putting people’s health more at risk due to exposure to high NO2 concentrations. This is worrying for the citizens of Leicestershire as many sources claim Leicester to have the most traffic light in comparison to other UK cities .
The traffic lights in Leicester seem to be no longer fit for purpose as they pose as much of a health risk as a form of protection. It can be concluded that traffic lights provide short-term safety but in the long term will result in more health degradation for a greater number of people. It is apparent that to get Leicester off the most polluted cities in the UK list, and to provide better quality of air, the number of traffic lights must be reduced.
Possible solution to NO2 crisis
The UK is under a lot of pressure to improve its air quality. Quite recently our government failed to put forward an air quality plan to begin tackling UK’s illegal levels of pollution. Reducing the amount of NO2 pollutants is where we are struggling the most. Leicester is still recording concentrations well above the acceptable level. This project was designed to improve our understanding of how NO2 disperses across Leicestershire and through observed patterns, develop ideas to combat the extortionate NO2 emissions.
From the experiments conducted for this project, large water surfaces were discovered to be very effective in lowering NO2 concentrations. Nitrogen dioxide pollution is very high in Leicester and in order to make a significant difference, a similar surface area of the observed reservoirs would be required. Increasing the number of water foundations in the city can help but the surface area is not large enough to deplete the NO2 molecules at the rate the city needs. Due to the findings, extending the Grand Union Canal to branch into the city centre was put forward.
Figure 20: Canal scheme – branch created from Grand Union Canal, flowing down St. Margaret’s Way, continuing down Church Gate, then following High Street towards River Soar
St. Margaret’s Way can be used to feed the town centre with water from the Grand Union Canal. The left and right flowing traffic on St Margaret’s Way is separated by an area of land that is measured up to 5 m in width (narrowest width measured at 3.8 m). Currently, most of that space is covered by trees. The trees can be removed and replaced with a canal, 3m in width to run down St. Margaret’s Way towards the city centre. Just before entering the Churchgate streets, there is a complicated traffic light system on Vaughan Way road. A bridge/ flyover can be used to connect the roads above the proposed canal. Alternatively, an underground canal can be built before the complicated junction is approached. The canal would resurface at the entrance of Church Gate. If this project were to be implemented, vehicles would no longer have access to Church Gate road. This works perfectly with Leicester council’s ambition to deliver Phase 2 of ‘Connecting Leicester’ plan by extending pedestrianisation and removing vehicles from where they are not required in the city centre by 2019 . Church Gate road is 12 m in width. A 4 m wide canal can be built to run down the middle of Church Gate into the heart of town. Canal width of 4 m would provide plenty of space for pedestrians to walk on either side of the canal. A bridge can be constructed on Church Gate where Mansfield Street crosses over to allow traffic flow. The canal can then lead down the centre of High Street, where it is mainly pedestrians on foot so traffic disturbance would again be kept at a minimum. The High Street is 15 m wide so a canal with a width of 5 m is suitable for the area. Once the canal is in place the street would also be off limit to vehicles. At the end of the High Street, before the usual traffic is approached, an underground canal can be built for a link with River Sour to be made and the circuit would be complete.
The proposed canal route is estimated to cover approximately 4938 m2 of surface area. The dimensions of the canal fit in the middle of the investigated surface areas for the two reservoirs (338 142 m2 & 691 022 m2) in this report. It can therefore be confidently said that this proposal will enable sufficient levels of nitrogen dioxide molecules to react with water molecules. Not only would it make the town aesthetically pleasing, but it will also improve the quality of the air.
The layout of the canal can be improved and redesigned by someone more knowledgeable in the area. The presented layout seems to be the best way to introduce a canal into the city centre with minimal change to the traffic system.
The important aspect of this project was to put forward an idea that the Government itself is struggling with.
The project tested the limits of the Zephyr as it was taken on all sorts of on and off road journeys. Despite the differences in the environment (altitude/rural/urban), the Zephyr successfully managed to monitor and analyse atmospheric pollution.
The biggest issue the zephyr/MOS sensors face is resolving the warm up effect. Even after significant time was provided the MOS electrode to reach equilibrium (1 hour), the warm up effect was still observed in some experiments, which required repeating or removing half of the data; as seen on urban/rural experiment. There is no way of determining if the MOS sensors has reached equilibrium before carrying out the experiment. The sensors could be perfected if the time it took to reach equilibrium was improved.
The project revealed that the dispersion of NO2 is very complex and the environment plays a big part on how it is distributed and how it can also be controlled.
The hot air balloon experiment provided many insightful results. If enough pollution is generated in a city, the wind can transport the pollution to neighbouring cities that are a couple of hours away due to its moderately long lifespan. The results from graph 8 showed that the NO2 diffuses vertically upwards at a near perfect constant rate. The observed linear relationship between increasing altitude and the dilution of NO2 is due to removing the influence of the fluctuating wind since both the balloon (sensor) and plume experienced the same force by the wind. The experiment also concluded that motorways cause NO2 emissions from vehicles to be vertically dispersed at a very fast rate. It was concluded that the contribution of 3 factors enhanced the rate of vertical dispersion. Diffusion favouring more concentrated to less, convection causing rise from the temperature difference between hot exhaust and cooler surrounding air, and advection from the motorway induced vertical turbulence. First sign of the effect water surface had on NO2.
Measurements from the urban/rural regions showed city pollution is 41% higher than rural recordings. The results revealed the high vehicle density in the city was the reason for higher concentration of NO2 in urban areas. The experiment revealed that time also played a crucial role on the production of NO2 level. People face more NO2 exposure around 3pm due to schools finishing.
The project determined that the traffic lights on the A6 toward the train station is obsolete as it caused more harm than good. NO2 seemed to build up before the traffic lights. Pollution was also observed to be trapped in-between sets of traffic lights, creating NO2 hot spots and creating health risks. Although vehicles are the problem for the high NO2 concentration, they were also found to disperse NO2 via its movements.
The primary method for reducing pollution levels has always been focused on altering the source itself to make it a greener process, with less exhaust emissions. However, this experiment has successfully proven that the environment itself can be adapted and used to combat the pollution that is already present.
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