Visibility impairing aerosols in the urban atmosphere of Delhi

To study the visual air quality of Delhi, size fractionated aerosols – coarse and fine fractions of PM₁₀ – were collected and analysed for and EC at three sites with different background activities. The analysed species constitute a smaller portion of coarse fraction (39%) but a larger portion of fine fraction (69%). The sampling was performed from June 2003 to November 2003 which covers monsoon and post monsoon seasons.Aerosol data was used to describe the spatial variation of Visibility Range as a function of chemical composition of visibility impairing aerosols. During the study period, visibility was found to be poor varying between 4.7 and 13 km with an average value of 9.4 km. It is observed that visibility impairment was more due to carbonaceous aerosol followed by sulphate.     

Seasonal characteristics of haze observed by continuous visibility monitoring in the urban atmosphere of Kwangju, Korea

Continuous visibility monitoring has been carried out inKwangju, Korea since May 1999. The total light extinctioncoefficient b _ext measured by a transmissometer andreveals seasonal trends in urban visual air quality,especially under hazy conditions with a visual range of lessthan 15 km. Seasonal atmospheric visibility under lowrelative humidity during the winter was observed to be betterthan during any other seasons. Summertime visibility wasseverely degraded due to highly increased light scattering byhygroscopic particles under high humidity atmosphericconditions. Visibility during spring and fall was alsomoderate. However, yellow sand in spring caused the lowestvisibility conditions over the measurement area for a fewdays. With continuous monitoring using the transmissometer,the daily average seasonal visual range was measured to be13.1, 9.2, 11.0, and 13.9 km in spring, summer, falland winter, respectively. Under the atmospheric humiditycondition less than 60%, visual range was observed tobe 16.1, 13.9, 15.1, and 16.6 km in spring, summer,fall, and winter, respectively. The mean light extinctionbudget by sulfate and nitrate aerosols was determined to bethe highest value of 63.71% during the summer and thelowest value of 27.08% during spring. During the `yellow sand dust' period, a mean light extinction budget by soil particles was estimated to be at an unusually high value of 44.22%.