Lockdown morning haze due to dew, finds DU researcher
Representative imageNEW DELHI: Many wondered why even during the coronavirus-induced lockdown, there was morning haze despite the absence of vehicular traffic and industrial activities.
According to a research conducted by a group of scientists from India and Japan, and published in the journal Scientific Reports, it was the dew drops with fine particles that would uplift right after sunrise each morning and cause the haze, which would eventually evaporate once the sun’s radiation became bright.
Researchers also found that while there was haze, there was a reduction of sulphate ions and NO2 levels due to less traffic on the streets.
Lead author SK Dhaka, associate professor at Delhi University’s Rajdhani College, used the data from CPCB, DPCC, and a smart sensor developed by Nagoya University of Japan to monitor the environment at a very fine time resolution of 10 seconds for about 45 days, starting from March.
“It revealed that the morning haze resulted from uplifting of fine particles, which were reinforced by condensation of moisture following the sunrise. A profound steep rise in PM 2.5, after sunrise, for about two hours was observed almost all days in the first week of April 2020, suggesting evaporation of moisture from ground and trees contributing to the density of particles in the diameter range — 2.5 micron. Around 10 am, when the threshold solar radiation reached 350 watt/m (-2), the haze evaporated and a beautiful blue sky was seen in the observations,” Dhaka explained.
The associate professor stated that the first phase of lockdown in India, implemented from March 25 to April 14, resulted in a dramatic near-zeroing of various activities, except essential services. “With the help of Sachiko Hayashida from Research Institute for Humanity and Nature in Kyoto, we analysed variations in PM 2.5 over NCR. Measurements revealed large reductions (by 40-70%) in PM 2.5 during the first week of lockdown as compared to the pre-lockdown conditions.”
These observations were carried out using Compact and Useful PM2.5 Instrument and analysing data collected at eight monitoring stations in NCR. “During the lockdown, the peak PM 2.5 concentrations were found to be slightly lower in the morning and late night as wind speeds remained low and temperature hovered around 20° Celsius or less, which were favourable for non-dispersion of pollutants. These low temperatures and stagnation of wind movement in the absence of solar radiation contributed to the formation of haze,” Dhaka claimed.
According to a research conducted by a group of scientists from India and Japan, and published in the journal Scientific Reports, it was the dew drops with fine particles that would uplift right after sunrise each morning and cause the haze, which would eventually evaporate once the sun’s radiation became bright.
Researchers also found that while there was haze, there was a reduction of sulphate ions and NO2 levels due to less traffic on the streets.
Lead author SK Dhaka, associate professor at Delhi University’s Rajdhani College, used the data from CPCB, DPCC, and a smart sensor developed by Nagoya University of Japan to monitor the environment at a very fine time resolution of 10 seconds for about 45 days, starting from March.
“It revealed that the morning haze resulted from uplifting of fine particles, which were reinforced by condensation of moisture following the sunrise. A profound steep rise in PM 2.5, after sunrise, for about two hours was observed almost all days in the first week of April 2020, suggesting evaporation of moisture from ground and trees contributing to the density of particles in the diameter range — 2.5 micron. Around 10 am, when the threshold solar radiation reached 350 watt/m (-2), the haze evaporated and a beautiful blue sky was seen in the observations,” Dhaka explained.
The associate professor stated that the first phase of lockdown in India, implemented from March 25 to April 14, resulted in a dramatic near-zeroing of various activities, except essential services. “With the help of Sachiko Hayashida from Research Institute for Humanity and Nature in Kyoto, we analysed variations in PM 2.5 over NCR. Measurements revealed large reductions (by 40-70%) in PM 2.5 during the first week of lockdown as compared to the pre-lockdown conditions.”
These observations were carried out using Compact and Useful PM2.5 Instrument and analysing data collected at eight monitoring stations in NCR. “During the lockdown, the peak PM 2.5 concentrations were found to be slightly lower in the morning and late night as wind speeds remained low and temperature hovered around 20° Celsius or less, which were favourable for non-dispersion of pollutants. These low temperatures and stagnation of wind movement in the absence of solar radiation contributed to the formation of haze,” Dhaka claimed.
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