Heterogeneous nucleation measurements in a sheathed planar diffusive condensation particle counter

Area of Science:

• Atmospheric Chemistry
• Physical Chemistry
• Aerosol Science

Background:

• Heterogeneous nucleation studies require controllable uniform saturation ratios (S).
• Diffusive Condensation Particle Counters (DCPCs) have potential for these studies if S-variation is minimized.
• Increasing sheath gas proportion (σ) can reduce S-variation in DCPCs.

Purpose of the Study:

• To investigate the feasibility of using a fast CPC to measure heterogeneous nucleation.
• To evaluate the effect of sheath gas proportion (σ) on the activation probability (P) of specific clusters.
• To assess the potential for determining aerosol size distributions using this method.

Main Methods:

• Measured activation probability (P) of Tetraheptylammonium Bromide cluster cations in a fast CPC.
• Controlled saturation ratios (S) via temperatures (T_s, T_c).
• Varied sheath gas proportion (σ) and cluster size (n) using high-resolution mobility selection.

Main Results:

• Activation probability curves P(T_s,n) rose sharply with increasing n and T_s.
• Increasing σ up to 75% increased the steepness of these curves five-fold.
• Measurements indicated potential for high-resolution aerosol size distribution determination.

Conclusions:

• Basic heterogeneous nucleation measurements are feasible with current CPC technology.
• Increasing sheath gas proportion (σ) significantly improves instrument performance for nucleation studies.
• Further instrument improvements are necessary for optimal heterogeneous nucleation research.