The issue of urban air quality has been a major concern all over the universe. This is because air quality and pollution have been recognised globally as pressing environmental issues ( Krivoruchko, 1999 ) . Since the London smog of 1952 that led to decease of more than 4000 people, the Governments of United Kingdom both at the national and local degrees have been doing conjunct attempts to better air quality by commanding emanations of pollutants into the ambiance through statute laws and other steps.
This survey aims to measure the recent sulfur dioxide ( SO2 ) emanations from 38 monitoring sites across London. The appraisal will no doubt supply more penetrations that will policy shapers in inventing schemes that will assist in commanding the emanation of pollutants into the ambiance.
1. 1 Sulphur Dioxide ( SO2 ) Emissions in UK
Sulphur dioxide is one of the eight chief air pollutants in the UK ‘s Air Quality Strategy. It is produced by firing coal and oil. “ Sulphur dioxide ( SO2 ) is a colourless, non-flammable gas with a perforating odour that irritates the oculus. It reacts on the surface of a assortment of airborne solid atoms, is soluble in H2O and can be oxidised within airborne H2O droplets ” ( Encyclopaedia of Atmospheric Environment, 2000 ) . SO2 emanations are chiefly from power Stationss, oil refineries and big industrial workss. The chart below shows 1998 SO2 emanation beginnings in UK.
hypertext transfer protocol: //www.ace.mmu.ac.uk/eae/Figures/UK_SO2.jpg
Adapted from ( Encyclopaedia of Atmospheric Environment, 2000 )
The information for this analysis comprise of SO2 monitored degrees recorded in parts per billion ( ppb ) between January 2008 to September 2009 and their monitored sites across London. The informations were obtained from the London Air Quality Network ( LAQN ) . The datasets were examined in Excel Worksheet, look intoing the columns and rows by oculus. After careful scrutiny of the informations, the undermentioned issues were identified in the information.
Some SO2 measurings were recorded with negative values. Basically, in a monitoring site there could be either a positive reading or no reading recorded at all. Therefore, all the negative values were assigned positive values
Site TK3 was non shown as one of the SO2 monitored sites during the monitoring period under consideration but was populated with some readings in the value Fieldss. This could be a error during the procedure of recording of the data.To avoid any colored analysis, TK3 was removed in the value field.
Brent 2 ( BT2 ) has merely reading on 31/8/2009 but no readings from 01/01/2008 – 30/8/2009.
Croydon 4 ( CR4 ) merely has merely reading on 31/8/2009 but no SO2 readings from 01/01/2008 – 30/8/2009.
Teddington ( TDO ) no SO2 readings from 01/01/2008 – 30/8/2009.
Probe of the information reveals hapless informations recordings in LAQN database. It is good that to hold records of air pollutants emanations but much more has to be done on the issue of informations quality given to the populace. Recording of informations such as this should be automated.
After scrutiny of the informations and necessary redacting done, a map demoing SO2 measured values for each monitoring site was created in the Arc Map utilizing London Wards as a background.
The map above shows the cumulative sulfur dioxide concentration degrees in assorted sites in London. There were high concentrations of SO2 in locations like Lambeth 1, Lambeth 3, Lambeth 4, Greenwich, Berkley, Newham 2, Thurrock 1, Crystal Palace, Lewisham 1 etc, while there somewhat low SO2 concentration in locations like Tower Hamlet 1 and Westminster. Castle Point, Thurrock 1, Sevenoaks background and Elmbridge are non within the London wards.
The histogram chart of the concentration map is shown below.
Histogram of relative symb.jpg
Since some concentrations of SO2 are clustered, it is possible to find hot and cold pots in the information by looking for bunchs of sites with high values and bunchs of sites with low values. With the informations available, it is besides possible to make SO2 one-year norm maps ( for 2008 and 2009 ) . Monthly upper limit of SO2 values for each site can besides be mapped.
3.0 Modeling Approach:
Laqn.dbf and Location.dbf informations provide merely information on SO2 emanation values at monitored locations across London. These informations entirely are unequal to foretell SO2 degrees across London. Dispersion Models can be used to see the spacial distribution of SO2 concentrations and so do estimations of SO2 degrees at unsampled sites. However, Dispersion theoretical account will necessitate informations like SO2 emanation beginnings and local meteoric information such as air current velocity, wind way etc. , which are non available. An option here is to utilize Interpolation methods which will utilize SO2 monitored informations, and effort to gauge concentrations at unsampled locations by suiting surfaces through the monitored information points ( APMoSPHERE Project, 1998 ) . “ Interpolation is described as process of foretelling the value of property at unsampled site from measurings made at location within the same country or part. Interpolation is necessary when the land truth informations do non cover the sphere of involvement wholly ” ( Othman 2009 ) . There are two types of insertion ; Deterministic and Geostatistical insertions.
Simple Kriging – geostatistical insertion theoretical account was used here. “ Kriging operates by gauging different constituents of fluctuation, and utilizing the ensuing theoretical accounts to gauge conditions at unsampled locations ” ( APMoSPHERE Project ) . Three types of Kriging are widely used in geostatistical analysis are ; Ordinary and simple kriging which histories for merely local-scale fluctuation in the variable of involvement ; cosmopolitan kriging takes history of long-range fluctuation or impetus as instance may be and co-kriging employs extra information on exogenic variables, covariates to assist in foretelling local fluctuations. ( APMoSPHERE Project ) .
Simple Kriging in Geostatistical Analyst of ArcGIS was explored here. The theoretical account is Gaussian based.
SO2 degrees ( Value property )
Simple Kriging – Semivariogram
Prediction Map – Gaussian Contour Surface
Using ArcGIS, a semi-variogram theoretical account was foremost created to cognize how spacial dependant the information.
Semi-variogram Graph – Simple Kriging
The graph of semi-variogram below shows that the information has weak spacial dependance which means that it will be hard to do anticipations where SO2 emanations are non monitored.
In cross proof nosologies graph, about all the points are spread along the horizontal line ( the measured or observed line ) which makes anticipations hard here. There are besides broad spread in the mean difference between the measured and predicted values. The sum-up of anticipation mistakes is presented in the tabular array below:
Summary tabular array of Simple Kriging – Prediction
Average Standard Mistake
Arrested development map – 0.034*x + 1.263. The average tends towards normalcy and RMSE about approaches one. Finally, the anticipation end product map is produced.
3.2 Consequences and Discussion:
Simple kriging geostatistical tool was merely explored here. No anticipations were made due to insufficiency of the information available. The information provide merely information on SO2 emanation values at monitored locations across London. It did non state the relationships between the SO2 emanations and other variables emanation beginnings etc.
4.0 Analysing Exposure and Health Impacts of SO2 and other Air Pollutants across London
There has been a turning concern about the impact of SO2 and other air pollutants on person ‘s wellness. Many surveies have suggested that people enduring from asthma and other respiratory diseases may be peculiarly susceptible to the inauspicious effects of sulfur dioxide. SO2 pollution is considered more harmful when particulate and other pollution concentrations are high.
In this appraisal, an effort was made to gauge the possible persons ‘ exposures to SO2 pollution utilizing the datasets available. Valuess from simple kriging predicted surface map were extracted utilizing Zonal Statisticss in Spatial Analyst tools of ArcGIS. Mean was used as chart statistics. The end product file was so joined with London Wards attribute information.The Sum_Bad Health field was normalised with Kriging Mean utilizing Symbology builder.
Heallth hazard map.jpg
The map above shows the likely figure of people in the London Wards to be affected by the SO2 pollution.
Ideally, informations demoing hospital admittances on respiratory and other health-related diseases would be required to gauge the likely figure of people to be affected. it with SO2 degrees informations and attribute information in the London Ward.
To a big extent, truth of any geospatial analysis depends upon the quality of the informations being used. There were some many issues observed in the information for this appraisal. Examination of the information showed hapless recording of the informations in the LAQN database. The attribute information on the information was non plenty for any complete appraisal. Laqn. information contains merely SO2 values recorded in parts per billion. It did non state us the relationship between these values and other variable of involvements.
London Air Quality Network may see it utile to automatize the whole procedure of their informations recording as this will to some extent guard against human mistakes.
Issues on the adopted modeling attack
As with every theoretical account there are many restrictions associated***** Kriging geostatistical tool was used for the insertion. It provides a good interpolator for thin informations like SO2 degrees. Simple Kriging uses a semivariogram, a step of spacial correlativity between two points, so the weights change harmonizing to the spacial agreement of the samples. “ It provides a step of the mistake or uncertainness ( of the estimated surface ” ( Othman 2009 ) .
Kriging restrictions – Mistake appraisal depends on variograms and distribution of information points and size of interpolated blocks. Kriging requires attention when patterning spacial correlativity construction. It,