Abundant nitrogenous secondary organic aerosol formation accelerated by cloud processing

Area of Science:

• Atmospheric Chemistry
• Aerosol Science
• Cloud Microphysics

Background:

• Nitrogenous organic (CHON) compounds are vital components of secondary organic aerosols (SOA).
• The formation mechanisms of CHONs within cloud environments remain poorly understood.
• Cloud processes (CPs) are hypothesized to influence CHON speciation and abundance.

Purpose of the Study:

• To investigate the transformation pathways of CHONs during cloud processes.
• To elucidate the role of aqueous phase reactions in CHON formation within clouds.
• To quantify the contribution of CPs to CHON diversity and abundance.

Main Methods:

• Modeling aqueous phase reactions of carbonyl-containing biogenic volatile organic compound (BVOC) ozonolysis intermediates with ammonia (NH3).
• Analysis of CHON speciation, including oxygen atom counts and double bond equivalents (DBE).
• Quantification of CHON formation pathways attributed to cloud processes.

Main Results:

• Cloud processes significantly enhance the diversity of CHONs, with oxygen counts from 1-10 and DBE values from 2-10.
• Aqueous phase reactions involving NH3 and CHO precursors are proposed as a key CHON formation pathway.
• This mechanism accounts for approximately 75% of CHONs by number in cloud water.
• Reactions between NH3 and BVOC ozonolysis intermediates form about two-thirds of all CHONs.

Conclusions:

• Cloud processes play a critical role in the formation and evolution of nitrogenous organic compounds in the atmosphere.
• Aqueous phase reactions, particularly involving ammonia, are a major driver of CHON formation in clouds.
• Understanding CHON formation during CPs is essential for accurately modeling SOA composition and climate impacts.