title: Automobile exhaust gas as a source of aqueous phase OH radical in the atmosphere and its effects on physiological status of pine trees.
abstract: Free radical generation potential of automobile exhaust gas was examined by measuring hydroxyl (OH) radical photo-formation rates in exhaust gas-scrubbing water. Effects of automobile exhausts on physiological status of Japanese red pine trees (Pinus densiflora Sieb. et Zucc.) were also investigated to elucidate the mechanism how the free radicals derived from exhaust gas damage higher plants. Gasoline and diesel exhaust gases were scrubbed into pure water. Potential photo-formation rates of OH radical in aqueous phase (normalized to sun light intensity of clear sky midday on May 1 at 34°N) for gasoline and diesel cars were ave. 51 and 107 μ Mh⁻¹ m⁻³ of exhaust gas, respectively. Nitrite was a dominant source (ca. 70-90%) of photochemical formation of OH radical in both gasoline and diesel car exhausts. The scrubbed solution of diesel car exhaust gas was sprayed for six times per week to needles of pine tree seedlings in open top chambers. Control, exhaust+mannitol (added as OH radical scavenger), and nitrite+nitrate standard solution (equivalent levels existed in the exhaust gas) were also sprayed. Two months sprays indicated that the sprayed solutions of diesel exhaust and nitrite+nitrate caused a decrease of maximum photosynthetic rate and stomata conductance in pine needles while the control and exhaust+mannitol solution showed no effects on photosynthetic activities of pine needles. These results indicated that OH radicals generated mainly from photolysis of nitrite occurring in the scrubbing solution of exhaust gas are responsible for the decrease of photosynthetic activities of pine needles.
authors.affiliation: Department of Environmental Dynamics and Management, Graduate School of Biosphere Science, Hiroshima University, Higashi-Hiroshima 739-8521, Japan. hsakuga@hiroshima-u.ac.jp
authors.forename: Hiroshi
authors.initials: H
authors.lastname: Sakugawa
authors.forename: Toshihide
authors.initials: T
authors.lastname: Matsuda
authors.forename: Nobutake
authors.initials: N
authors.lastname: Nakatani
mesh_terms: D000393:Air Pollutants / Q000032:analysis / Q000378:metabolism*; D001272:Atmosphere / Q000032:analysis*; D005740:Gases / Q000032:analysis / Q000378:metabolism*; D017665:Hydroxyl Radical / Q000032:analysis / Q000378:metabolism*; D009573:Nitrites / Q000032:analysis; D010788:Photosynthesis; D028223:Pinus / Q000378:metabolism*; D001335:Vehicle Emissions / Q000032:analysis*
chemical_list: D000393:Air Pollutants; D005740:Gases; D009573:Nitrites; D001335:Vehicle Emissions; D017665:Hydroxyl Radical