Fig. 3.

Particle shape changes and element distributions in an aged sample from flight 3. (A) TEM image of fresh BB sample with photochemical age of 0.34. Many grains of K₂SO₄ and KCl as well as ns-soot are embedded within organic matter spread over the substrate. (B) TEM image of moderately aged sample with photochemical age of 0.62. Particles have increased viscosities and appear round but not spherical. (C) TEM image of aged sample with photochemical age of 0.97. Particles have become spherical, and the tarball number fraction increased. (D) Element mapping images of the TEM image in C. C, O, N, and Cl occur in all particles, whereas K and S are embedded within some tarballs or other OA particles and appear as dark inclusions in the TEM image in C. Colors indicate normalized EDS intensities for each element.