| Title: | Heterogeneous Reactions of Limonene on Mineral Dust: Impacts of Adsorbed Water and Nitric Acid |
| Author(s): | Lederer MR; Staniec AR; Coates Fuentes ZL; Van Ry DA; Hinrichs RZ; |
| Address: | "Department of Chemistry, Drew University , Madison, New Jersey 07940, United States" |
| ISSN/ISBN: | 1520-5215 (Electronic) 1089-5639 (Linking) |
| Abstract: | "Biogenic volatile organic compounds (BVOCs), including the monoterpene limonene, are a major source of secondary organic aerosol (SOA). While gas-phase oxidation initiates the dominant pathway for BVOC conversion to SOA, recent studies have demonstrated that biogenic hydrocarbons can also directly react with acidic droplets. To investigate whether mineral dust may facilitate similar reactive uptake of biogenic hydrocarbons, we studied the heterogeneous reaction of limonene with mineral substrates using condensed-phase infrared spectroscopy and identified the formation of irreversibly adsorbed organic products. For kaolinite, Arizona Test Dust, and silica at 30% relative humidity, GC-MS identified limonene-1,2-diol as the dominant product with total organic surface concentrations on the order of (3-5) x 10(18) molecules m(-2). Experiments with (18)O-labeled water support a mechanism initiated by oxidation of limonene by surface redox sites forming limonene oxide followed by water addition to the epoxide to form limonenediol. Limonene uptake on alpha-alumina, gamma-alumina, and montmorillonite formed additional products in high yield, including carveol, carvone, limonene oxide, and alpha-terpineol. To model tropospheric processing of mineral aerosol, we also exposed each mineral substrate to gaseous nitric acid prior to limonene uptake and identified similar surface adsorbed products that were formed at rates 2 to 5 times faster than without nitrate coatings. The initial rate of reaction was linearly dependent on gaseous limonene concentration between 5 x 10(12) and 5 x 10(14) molecules cm(-3) (0.22-20.5 ppm) consistent with an Eley-Rideal-type mechanism in which gaseous limonene reacts directly with reactive surface sites. Increasing relative humidity decreased the amount of surface adsorbed products indicating competitive adsorption of surface adsorbed water. Using a laminar flow tube reactor we measured the uptake coefficient for limonene on kaolinite at 25% RH to range from gamma = 5.1 x 10(-6) to 9.7 x 10(-7). After adjusting for reactive surface areas, we estimate uptake coefficients for limonene on HNO(3)-processed mineral aerosol on the order of (1-6) x 10(-6). Although this heterogeneous reaction will not impact the atmospheric lifetime of gaseous limonene, it does provide a new pathway for mineral aerosol to acquire secondary organic matter from biogenic hydrocarbons, which in turn will alter the physical properties of mineral dust" |
| Keywords: | Adsorption Cyclohexenes/*chemistry Dust Limonene Minerals/*chemistry Nitric Acid/*chemistry Surface Properties Terpenes/*chemistry Water/*chemistry; |
| Notes: | "MedlineLederer, Madeline R Staniec, Allison R Coates Fuentes, Zoe L Van Ry, Daryl A Hinrichs, Ryan Z eng 2016/12/10 J Phys Chem A. 2016 Dec 8; 120(48):9545-9556. doi: 10.1021/acs.jpca.6b09865. Epub 2016 Nov 21" |
