Reaction of isoprene on thin sulfuric acid films: kinetics, uptake, and product analysis.
A high vacuum Knudsen flow reactor was used to determine the reactive uptake coefficient, gamma, of isoprene on sulfuric acid films as a function of sulfuric acid weight percent, temperature, and relative humidity. No discernible dependence was observed for gamma over the range of temperatures (220 - 265 K) and pressures (10(-7) Torr -10(-4) Torr) studied. However, the uptake coefficient increased with increased sulfuric acid concentration between the range of 78 wt % (gamma(i) approximately 10(-4)) and 93 wt % (gamma(i) approximately 10(-3)). In addition to the Knudsen Cell, a bulk study was conducted between 60 and 85 wt % H(2)SO(4) to quantify uptake at lower acid concentrations and to determine reaction products. After exposing sulfuric acid to gaseous isoprene the condensed phase products were extracted and analyzed using gas chromatography/mass spectrometry (GC/MS). Isoprene was observed to polymerize in the sulfuric acid and form yellow/red colored monoterpenes and cyclic sesquiterpenes. Finally, addition of water to the 85 wt % sulfuric acid/isoprene product mixture released these terpenes from the condensed phase into the gas phase. Together these experiments imply that direct isoprene uptake will not produce significant SOA; however, terpene production from the small uptake may be relevant for ultrafine particles and could affect growth and nucleation.
Connelly
Brandon M
BM
The Cooperative Institute for Research in Environmental Sciences, The Department of Chemistry and Biochemistry, University of Colorado, Boulder, Colorado 80309-0216, USA.
Tolbert
Margaret A
MA
D001272:Atmosphere / Q000737:chemistry; D002070:Butadienes / Q000737:chemistry*; D008401:Gas Chromatography-Mass Spectrometry; D005740:Gases / Q000737:chemistry; D045782:Hemiterpenes / Q000737:chemistry*; D007700:Kinetics; D010420:Pentanes / Q000737:chemistry*; D013464:Sulfuric Acids / Q000737:chemistry*; D013997:Time Factors
D002070:Butadienes; D005740:Gases; D045782:Hemiterpenes; D010420:Pentanes; D013464:Sulfuric Acids; C005059:isoprene; C033158:sulfuric acid