Hygroscopic organic aerosols during BRAVO?

Area of Science:

• Atmospheric chemistry and physics
• Aerosol science

Background:

• The hygroscopic properties of organic aerosols, crucial for understanding their climate impact, remain poorly understood.
• Organic aerosols constitute a significant fraction (22% on average) of fine particulate matter (PM2.5).

Purpose of the Study:

• To investigate the water uptake of organic aerosols as a function of relative humidity (RH).
• To assess the contribution of organic aerosols to aerosol light scattering during the Big Bend Regional Aerosol and Visibility Observational Study (BRAVO).

Main Methods:

• Utilized data from the 1999 BRAVO field campaign.
• Estimated PM2.5 light scattering (Bsp) using aerosol chemical composition and dry particle size distributions at varying RH.
• Analyzed RH conditions, noting hourly RH exceeded 80% only 3.5% of the time, averaging 44%.

Main Results:

• Inorganic species' liquid water growth adequately explained measured PM2.5 light scattering (Bsp) at RH levels between 70% and 95%.
• The study focused on conditions where RH rarely exceeded 80%.

Conclusions:

• The contribution of organic aerosol hygroscopicity to light scattering may be less significant than previously assumed under the studied conditions.
• Further research is needed to fully elucidate the role of organic aerosols in atmospheric processes, particularly under high humidity conditions.