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OpinionLetters

Letters to the Editor, March 3, 2014

I wish to correct the report ("Air pollution worst in 18 years in shopping areas", February 24). Your report was based on research by Friends of the Earth. The group says in 2013 there were 184 days where the roadside air pollution index (API) exceeded 100, and last year was the worst on record. The number of such days was in fact 132.

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Letters

I wish to correct the report ("Air pollution worst in 18 years in shopping areas", February 24).

Your report was based on research by Friends of the Earth. The group says in 2013 there were 184 days where the roadside air pollution index (API) exceeded 100, and last year was the worst on record. The number of such days was in fact 132.

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The number of days with roadside API exceeding 100 in 2010, 2011 and 2012 were 141, 172 and 142 days, respectively.

Having understood Friends of the Earth's methodology, we have explained to it its two errors, and we also issued our own press release for clarification.

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The group's first error was that it averaged out the hourly API and counted those days with "daily average" greater than 100. As the API was reported on an hourly basis, it is inappropriate to calculate and use the "daily averages" for determining the number of days with the API exceeding 100.

The second error was that Friends of the Earth added up all individual roadside roadsides' figures to give the overall roadside figure. It overlooked that the API greater than 100 would normally also be observed simultaneously at more than one station and hence adding up all individual stations' figures would double or even triple count some of these daily figures.

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