Local emission rather than weather with poor wind

Pollution levels and wind speeds
This figure shows the level of a traffic-related air pollutant, nitrogen dioxide (NO₂), recorded by EPD urban rooftop and roadside monitors as well as by a rural background monitor in Tap Mun (Grass Island) in 2009. NO₂ daily average concentrations in Autumn (Sept to Nov) were grouped together by three levels of wind-speed: “Low”, “Medium” and “High” were defined as days with wind-speed lower than the 25^th percentile, from the 25^th to 75^th percentile, and higher than the 75^th percentile in the year respectively. Point estimates of the mean NO₂ concentrations and the 95% confidence intervals are shown in the figure. Similar patterns were found among other seasons of the year and other pollutants.

Our results indicate clearly that in the absence of traffic emissions, as in the location of the rural background monitor in Tap Mun, air quality could be well below (that is, compliant with) the WHO annual AQG of 40 μgm^-3. However, in the presence of traffic emissions, the concentrations of NO₂ far exceeded the safer WHO guideline by up to 300% on days with poor wind dispersion. Although air pollution levels were lower on days with higher wind-speeds, the 50% reduction due to windy weather effect was very small when compared with the 1200% reduction due to removal of traffic emissions.

Epidemiologic evidence just published in the past few months shows that exposure to vehicular source pollutants (including NO₂ and black carbon) increases the risk of blood cancer in children (Amigou et al 2010) and shortening of genetic sequences in human body cells (McCraken et al 2010), which is a cause of cell replication problems leading to aging, heart disease, and cancers.

Attributing our air quality problems to regional or meteorological reasons cannot help in achieving the WHOAQG and improve public health. The wind only blows Hong Kong's pollutants into our neighbours' backyard.

Edited by AJH

References:

Amigou A, Sermage-Faure C, Orsi L, Leverger G, Baruchel A, Bertrand Y, Nelken B, Robert A, Michel G, Margueritte G, Perel Y, Mechinaud F, Bordigoni P, Hémon D, Clavel J. Road Traffic and Childhood Leukemia: The ESCALE Study (SFCE). Environ Health Perspect. 2011 Apr;119(4):566-72. Epub 2010 Dec 8.

McCracken J, Baccarelli A, Hoxha M, Dioni L, Melly S, Coull B, Suh H, Vokonas P, Schwartz J. Annual ambient black carbon associated with shorter telomeres in elderly men: Veterans Affairs Normative Aging Study. Environ Health Perspect. 2010 Nov;118(11):1564-70.