Ventilation coefficient over a tropical indian station, Gadanki (13.5°N, 79.2°E)

Extensive observations of the atmospheric boundary layer height and wind speed using an L-band UHF

wind profiler were utilized to estimate ventilation coefficient (VC), an index of air pollution potential over Gadanki (13.5°N, 79.2°E), a tropical Indian station during the period from March 1999 to April 2000. On an average, maximum boundary-layer height was observed during pre-monsoon period with the highest value (~ 2.3 km) in April and minimum during winter (~ 1.4 km), with the lowest value in January. The daily, monthly and seasonal variations of VC were studied during this period. It was found that VC is high during noon hours, leading to less pollution potential during noon hours. VC is found to be low during winter period and high during monsoon period.

Ventilation coefficient

VC represents the rate at which the air within the convective boundary layer is transported. This parameter plays an important role in the dispersion of aerosols and is one of the factors that determine the pollution potential over a region of interest.

The VC is given by

VC = ZiU

where Zi is the ABL height and U is the average wind speed within the mixed layer

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(U= ∑Ui=∑Ui/n, i=1 to i=Zi, n is the number of levels within the ABL)

Read more:

• Krishnan, P., and Kunhikrishnan, P. K., Temporal variations of ventilation coefficient at a tropical Indian station using UHF wind profiler, Current Science , 86, 447-451, 2004.[PDF]

• (syntax correction: use the above equation for calculation of U.

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  • ∑ is missing in the paper (overbar on ∑U suggesting averaging)