"tendency_of_X" means derivative of X with respect to time. The construction "atmosphere_moles_of_X" means the total number of moles of X in the entire atmosphere, i.e. summed over the atmospheric column and over the entire globe. The chemical formula for alpha_pinene is C10H16. The IUPAC name for alpha-pinene is (1S,5S)-2,6,6-trimethylbicyclo[3.1.1]hept-2-ene.