Philip J. Dawson

Gaseous and particulate air pollution in the San Gabriel Mountains of Southern California

In order to assess concentrations and daily patterns of air pollutants at a mountainous site in the South Coast Air Basin, a study was undertaken in the San Dimas Experimental Forest of the San Gabriel Mountains between April 1985 and October 1985. Continuous monitoring of O3, NO, NO2, SO2, total S compounds and light scattering coefficient was conducted. Particulate aerosols were collected twice a week and concentrations of nitrate, ammonium and sulfate in fine ( 2.5 μm diameter) modes were determined. For the June–August period, when the levels of photochemical smog were the highest, monthly 24-h average concentrations of the pollutants were: O3, about 200 μg m−3; NO2, 40–75 μg m−3; NO, 1–5 μg m −3; and SO2, 0.5–5 μgm−3. The concentrations of O3 were about two times higher than in the neighboring stations of the South Coast Air Basin. O3, SO2 and total S concentrations peaked in the early afternoon, generally between 1500 and 1600 PST. Peak concentrations of NO occurred in the morning, generally between 1000 and 1100 PST. NO2 concentrations typically peaked in the late afternoon between 1500 and 1800 PST, but occasionally (in 9 % of days) maximum NO2 occurred in the morning, concurrently with the NO peaks. Daytime concentrations of the nitrate in fine aerosol fraction were generally between 100 and 600 nEq m −3, those of ammonium between 50 and 300 nEq m −3, and concentrations of sulfate between 60 and 250 nEq m−3. A 3-day denuder study showed that HNO3can make up to 73 % of the total amount of total nitrate in the air. NO2 was the most abundant N compound at Tan bark Flat (69–86% of the total amount of the monitored N compounds). Nitrate amounted to 9–15 %, HNO3 to 4–11 %, ammonium to 3–9%, and NO to 1–2% of the total amount of the measured nitrogen compounds.

Effects of ozone or sulfur dioxide on growth and yield of rice

Abstract Three cultivars of rice, Oryza sativa, M7, M9 and S201 were exposed in open-top field chambers to ozone and sulfur dioxide to determine the effects of these important air pollutants on field-grown plants. Exposures were for 15 weeks with ozone at 0, 98, 196, 294 or 392 μg m−3 for 5 h day−1, 5 days week−1, and sulfur dioxide at 131, 262, 393 or 524 μg m−3 for 24 h day−1, 5 days week−1. Three harvests of rice were made after 27 and 68 days and at the end of the exposures. At the first harvest following early plant growth, ozone at the highest concentrations resulted in reductions in growth whereas sulfur dioxide resulted in increased growth. At the second harvest, ozone-exposed plants continued to show reduced growth, whereas sulfur dioxide resulted only in reduced plant height. At the final and major harvest, ozone at 392 μg m−3 reduced total seed weight 12, 29 and 21% in cultivars M7, M9 and S201, respectively. Weight of 100 seeds and straw weight were reduced in M9 and S201 and percent seed sterility in panicles was increased. Ozone reduced height of all cultivars and increased the number of panicles. Sulfur dioxide at 524 μg m−3 reduced total seed weight of M9 and S201 by 22 and 14%, respectively, and weight per hundred seed by 11 and 10%, respectively. The results showed that ozone is much more injurious to rice per unit of pollutant than sulfur dioxide and that reduced yield due to both pollutants was caused mostly by reduced seed size. Increased seed sterility was partially offset by ozone exposure of the plants which produced more panicles. Cultivar M7 was more resistant to ozone or sulfur dioxide than M9 and S201.

Air Pollution Distribution Patterns in the San Bernardino Mountains of Southern California: a 40-Year Perspective

Since the mid-1950s, native pines in the San Bernardino Mountains (SBM) in southern California have shown symptoms of decline. Initial studies in 1963 showed that ozone (O3) generated in the upwind Los Angeles Basin was responsible for the injury and decline of sensitive trees. Ambient O3 decreased significantly by the mid-1990s, resulting in decreased O3 injury and improved tree growth. Increased growth of trees may also be attributed to elevated atmospheric nitrogen (N) deposition. Since most of the N deposition to mixed conifer forest stands in the SBM results from dry deposition of nitric acid vapor (HNO3) and ammonia (NH3), characterization of spatial and temporal distribution of these two pollutants has become essential. Although maximum daytime O3 concentrations over last 40 years have significantly decreased (~3-fold), seasonal means have been reduced much less (~1.5-fold), with 2-week long means occasionally exceeding 100 ppb in the western part of the range. In the same area, significantly elevated concentrations of HNO3 and NH3, up to 17.5 and 18.5 μg/m3 as 2-week averages, respectively, have been determined. Elevated levels of O3 and increased N deposition together with long-term drought predispose the SBM forests to massive bark beetle attacks making them susceptible to catastrophic fires.

Atmospheric dry deposition on pines in the Eastern Brook Lake Watershed, Sierra Nevada, California

Atmospheric dry deposition to branches of Pinus contorta and P. albicaulis was measured during summer 1987 in a sub-alpine zone at Eastern Brook Lake Watershed (EBLW), eastern Sierra Nevada, California. Results are presented as deposition fluxes of NO3−, SO42−, PO43−, Cl−, F−, NH4+, Ca2+, Mg2+, Na+, K+, Zn2+, Fe3+, Mn2+, Pb2+ and H+, and compared with other locations in California and elsewhere. Deposition fluxes of anions and cations to the pine branches were low, several times lower than the values determined near the Emerald Lake Watershed (ELW), another sub-alpine location in the western Sierra Nevada. The sums of deposition fluxes of the measured cations and anions to pine surfaces were similar, in contrast to the ELW location where the sums of cation fluxes were much higher than the sums of anion fluxes. A strong positive correlation between depositions of NO3− and NH4+, as well as SO42− and Ca2+, suggested that large portions of these ions might have originated from particulate NH4NO3 and CaSO4 deposited on pine surfaces. An estimated total N dry deposition (surface deposition of NO3− and NH4+ and internal uptake of NO2 and HNO3) to the forested area of the EBLW was 29.54 eq ha−1 yr− (about 414 g H ha−1 yr−1).

Effects of SO2 on physiology, elemental content and injury development of winter wheat

Abstract The effects of sulfur dioxide on buffering capacity, chlorophyll content, stomatal conductance, mineral composition and leaf injury of winter wheat ( Triticum aestivum , cv. Yecora Rojo) were studied. Plants were exposed to sulfur dioxide (0, 79, 183, and 393 μg m −3 ) in open-top chambers. Exposures were conducted in Riverside, California, during the coolest part of the year when the plants are believed to be more sensitive to sulfur dioxide than during the rest of the year. Physiological measurements, injury rating and collection of leaf material for chemical analysis were carried out after 22 days of exposure. The results of these measurements were compared with yield data from the final harvest which took place after 118 days of exposure. Elevated SO 2 concentrations caused decrease of buffering capacity, increase of total sulfur content and increase of injury of wheat leaves. These changes correlated significantly with reduction of total seed weight and weight of 100 wheat seeds at the final harvest. Stomatal conductance to water vapor, chlorophyll content and two leaf mineral concentrations (calcium, potassium) were not significantly affected by sulphur dioxide exposure. The results of this study indicated that buffering capacity, total sulfur content and injury of leaves could be used as early indicators of SO 2 stress in wheat and its subsequent yield losses.

Responses of Desert Annual Plants to Ozone and Water Stress in an in situ Experiment

Desert winter annual plants: Camissonia claviformis, C. hirtella, Caulanthus cooperi, Chaneactis carphoclinia, C. stevioides, Cryptantha angustifolia, C. pterocarya, Erodium cicutarium, Festuca octoflora, Lupinus concinnus, Oenothera californica, Plantago insularis, Platystemon californica, Salvia columbariae, Thelypodium lasiophyllum, and Thysanocarpus curvipes growing on irrigated and non-irrigated plots were exposed in situ to elevated levels of ozone dispensed from an open air exposure system. Plants were exposed intermittently to a gradient of ozone of concentrations ranging between 44 and 133 ppb (nL L−1) for 35 h over a total of 216 h. Only three species were injured by ozone at the highest ozone concentrations. Leaf injury to C. claviformis—2 percent total foliar injury (TFI), C. hirtella—1 percent TFI, and Erodium cicutarium—2 percent TFI, developed at the highest ozone concentrations. Leaf injury to these species was similar on the irrigated and nonirrigated plots. Leaf water potential and stoma...

Injury and physiological responses of Larrea tridentata (DC) coville exposed In situ to sulphur dioxide

The response of shrubs of Larrea tridentata (DEC) Coville (creosotebush) exposed to sulphur dioxide (SO(2)) was evaluated using in situ plants of the Majove Desert. Larrea was exposed to acute levels of 0.3 to 2.0 microl litre(-1) SO(2) for periods up to 13 days using field chambers or an open-air fumigation system. Plants exposed in the spring exhibited considerable leaf injury (necrosis and defoliation) when exposed to 2.0 microl litre(-1) SO(2), and in the autumn had leaf injury when exposed to >0.4microl litre(-1) SO(2). Injured plants had higher transpiration rates, less negative water pressure potentials, and/or lower photosynthetic rates than control plants. It is likely that Larrea would not be injured by the typically low SO(2) concentrations and dry environmental conditions of the Mojave Desert. However, if injury were to occur, it would be accompanied by changes in plant-water relations and photosynthesis, followed by recovery after the SO(2) stress was removed.