Vertically increased NO₃ radical in the nocturnal boundary layer.

Area of Science:

• Atmospheric Chemistry
• Air Quality Monitoring
• Boundary Layer Meteorology

Background:

• Nitrate radical (NO3) plays a crucial role in nocturnal atmospheric chemistry, oxidizing nitrogen oxides and hydrocarbons.
• Understanding the vertical distribution of NO3 and its precursors is vital for air quality assessments.

Purpose of the Study:

• To investigate the vertical profiles and diurnal variations of NO2, O3, and NO3 in the nocturnal boundary layer.
• To determine the factors influencing NO3 production, removal, and lifetime at different altitudes.

Main Methods:

• Utilized four differential optical absorption spectroscopy (DOAS) instruments for measurements.
• Analyzed vertical distributions and diurnal variations of NO2, O3, and NO3.
• Calculated NO3 production rates (PNO3) and lifetimes (τNO3).

Main Results:

• NO2, O3, and NO3 exhibited single diurnal peaks, with O3 and NO3 increasing with height, while NO2 decreased.
• NO3 production was sensitive to NO2 at higher altitudes and O3 near the ground.
• NO3 lifetime increased with height, influenced by relative humidity and PM2.5, with gas-phase reactions dominating at lower altitudes and N2O5 hydrolysis at higher altitudes.

Conclusions:

• Vertical profiles of NO3 are significantly influenced by atmospheric stability, humidity, and particulate matter.
• Increased NO3 radicals at higher altitudes may contribute to nitrate aerosol formation.
• Findings provide insights into nocturnal atmospheric processes and nitrate aerosol formation in urban environments.