relationships between wind fields and nitrogen dioxide ... · (january 2008 – november 2010)...

Relationships between Wind Fields and Nitrogen Dioxide Concentration :

Inner Bangkok Case Study

Pannee Cheewinsiriwat, Pongsri Chanhow Department of Geography, Faculty of Arts,

Chulalongkorn University, Thailand.

Topics

• NO2 Concentration in Bangkok

• Data Model and Analysis

– Wind direction

– Wind speed

• Conclusions

2 23-27 April 2012 Geospatial World Forum 2012, Amsterdam

NO2 Concentration in Bangkok


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The hourly average of NO2 concentrations in each month (January 2008 – November 2010)

23-27 April 2012 Geospatial World Forum 2012, Amsterdam

winter summer rainy

winter summer rainy

winter summer rainy

winter

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The hourly average of NO2 concentrations in the months of high (December 2009), intermediate (March 2010), and low (July 2010) concentrations


Data Model and Analysis

• Input data

– Wind direction/speed (met stations)

– NO2 concentration (PCD stations)

– Measured at 10am every day in December 2009, March 2010, and July 2010 (total 93 days)

• Analysis

– Correlation: wind direction VS NO2 concentration

– Correlation: wind speed VS NO2 concentration

23-27 April 2012 Geospatial World Forum 2012, Amsterdam 6

Wind Direction


Roads as a major NO2 source

• Weighted road value = road length * number of lanes

• Wind path = wind direction to the PCD stations

• Weighted road values of pixels on the wind path within 1 km. from each PCD station are accumulated, to compare with NO2 concentration

23-27 April 2012 Geospatial World Forum 2012, Amsterdam 8

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The RBF was performed by a GIS function • using at least 10 stations as input in the calculation • to produce wind direction raster surface


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50

100

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wind paths or flow directions • generated by a flow direction function in GIS


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Weighted road values (WR) of each cell within 1 km from a PCD station Flow accumulated function in GIS was then used

• to accumulate WR from those cells the wind blew to the target cells (PCD stations).


Results : Wind Direction

• The resultant data reveal that at the 0.01 significant level (one tail) wind direction has a weak positive correlation (0.11).

• This can be interpreted that if the wind blows in the direction that passes more NO2-generated sources higher NO2 concentration can be found at a target location.

• However, the low correlation value (0.11) indicates the weak relationship.


Data Model and Analysis : Wind Speed


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Wind speed data were interpolated using RBF • to generate a raster surface of wind speed


Results : Wind Speed

• The resultant data reveal that at the 0.01 significant level (one tail) wind speed has a small negative correlation (-0.232) with NO2 concentration.

• This can be interpreted that stronger wind speed generates less NO2 concentration.

• However, the low correlation value (-0.232) indicates a weak relationship between the two variables.


Conclusions

• Although the wind fields factor has a very small influence on the level of NO2 concentration in the inner Bangkok areas, the results seem to underline the influences of the wind directions created by urban area physical configurations that divert the NO2 from its normal paths to the PCD stations.

• High wind speeds seem to have the opposite effect as it carries NO2 away from the PCD stations.


Thank you

relationships between wind fields and nitrogen dioxide ... · (january 2008 – november 2010)...

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