Enhancement of atmospheric Hsub2/subSOsub4/sub / Hsub2/subO nucleation: organic oxidation products versus amines

摘要

Atmospheric H₂SO₄ / H₂O nucleation influencing effects havebeen studied in the flow tube IfT-LFT (Institute for Tropospheric Research –Laminar Flow Tube) at 293 ± 0.5 K and a pressure of 1 bar usingsynthetic air as the carrier gas. The presence of a possible backgroundamine concentration in the order of 107–108 molecule cm?3throughout the experiments has to be taken into account. In a first set ofinvestigations, ozonolysis of olefins (tetramethylethylene,1-methyl-cyclohexene, α-pinene and limonene) for close toatmospheric concentrations, served as the source of OH radicals and possiblyother oxidants initiating H₂SO₄ formation starting from SO₂.The oxidant generation is inevitably associated with the formation oforganic oxidation products arising from the parent olefins. These products(first generation mainly) showed no clear effect on the number of nucleatedparticles within a wide range of experimental conditions for H₂SO₄concentrations higher than ~107 molecule cm?3. Alsothe early growth process of the nucleated particles was not significantlyinfluenced by the organic oxidation products in line with the expectedgrowth by organic products using literature data. An additional,H₂SO₄-independent process of particle (nano-CN) formation wasobserved in the case of α-pinene and limonene ozonolysis forH₂SO₄ concentrations smaller than ~107 molecule cm?3. Furthermore, the findings confirm the appearance of anadditional oxidant for SO₂ beside OH radicals, very likely stabilizedCriegee Intermediates (sCI). A second set of experiments has been performedin the presence of added amines in the concentrations range of a few107–1010 molecule cm?3 applying photolytic OH radicalgeneration for H₂SO₄ production without addition of otherorganics. All amines showed significant nucleation enhancement withincreasing efficiency in the order pyridine < aniline < dimethylamine < trimethylamine. This result supports the idea ofH₂SO₄ cluster stabilization by amines due to strongH₂SO₄?amine interactions. On the other hand, thisstudy indicates that for organic oxidation products (in presence of thepossible amine background as stated) a distinct H₂SO₄ / H₂Onucleation enhancement can be due to increased H₂SO₄ formationcaused by additional organic oxidant production (sCI) rather than bystabilization of H₂SO₄ clusters due toH₂SO₄?organics interactions.