Atmospheric Sulfuric Acid Dimer Formation in a Polluted Environment

Area of Science:

• Atmospheric Chemistry
• Aerosol Science
• Environmental Science

Background:

• New particle formation (NPF) significantly impacts atmospheric particle concentrations and cloud condensation nuclei (CCN).
• Sulfuric acid dimer formation is a critical step in NPF within sulfur-rich environments.

Purpose of the Study:

• To investigate the sulfuric acid dimer formation process in a sulfur-rich atmosphere.
• To determine the dominant mechanism (AA or AB) for dimer formation using field measurements.

Main Methods:

• Measured sulfuric acid monomer and dimer concentrations in Atlanta, USA.
• Applied sub-collision and collision ion-induced clustering (IIC) corrections to dimer concentrations.
• Utilized two acid-base mechanisms (AA and AB) to estimate evaporation rates.

Main Results:

• Average sulfuric acid concentrations ranged from 1.7 × 10^7 to 1.4 × 10^8 cm^-3.
• Neutral dimer concentrations were 4.1 × 10^5–5.0 × 10^6 cm^-3 (sub-collision) and 2.6 × 10^5–2.7 × 10^6 cm^-3 (collision IIC).
• Evaporation rates for dimers (0.1–1.3 s^-1) were higher than for acid-amine complexes (1.2–13.1 s^-1).

Conclusions:

• The AA mechanism is likely dominant in sulfuric acid dimer formation.
• More volatile dimers formed via the AA mechanism play a crucial role in initial cluster formation.
• Findings advance understanding of atmospheric aerosol formation and its climate implications.