During which times is the diurnal low typically measured?

The diurnal low refers to the period when atmospheric gas concentrations, such as CO2, are typically at their lowest levels during a 24-hour cycle. This phenomenon is often influenced by various environmental factors, including temperature and human activity. The correct timing for measuring the diurnal low is during the early morning hours, specifically between 2 AM to 4 AM, when there is minimal human activity and lower temperatures, allowing for the least fluctuations in gas levels.

The other time listed, from 2 PM to 4 PM, is generally not associated with the diurnal low since this period can experience increased activity and temperatures, leading to higher concentrations of various gases due to factors such as photosynthesis and higher ambient temperatures. Thus, the combination of 2 AM to 4 AM captures the essence of the diurnal low most accurately, while still allowing for some potential influence from evening and nighttime conditions, which further stabilizes lower readings.