The deep blue day is decreasing in China

Area of Science:

• Atmospheric Science
• Environmental Science
• Climatology

Background:

• Deep blue skies indicate low aerosol concentrations and clear conditions, vital for human living environments.
• Increasing human emissions may lead to a decline in deep blue sky days, signaling environmental degradation.

Purpose of the Study:

• To investigate long-term changes in deep blue sky days in China from 1980 to 2018.
• To analyze the contributing factors, including air pollution and meteorological conditions, to the observed trends.

Main Methods:

• Utilized atmospheric visibility and low cloud cover data to classify blue sky days (light, medium, deep blue) due to lack of direct measurements.
• Analyzed trends in annual deep blue days across China over a 39-year period.

Main Results:

• A significant decreasing trend in annual deep blue days was observed across most of China, with an average decrease of -0.48 days per year.
• The decline became more pronounced after 2013, with the most substantial decrease in eastern China, particularly during winter.
• Decreased surface wind speed, increased air temperature, decreased relative humidity, and rising pollution emissions contributed to fewer deep blue sky days.

Conclusions:

• Long-term air pollution and meteorological changes have led to a significant reduction in deep blue sky days in China.
• The observed trend suggests a decline in environmental quality, especially impacting winter conditions.