Acid Mist Treatment Research Articles

Structural and interface engineering of Co nanocatalysts induce boosting the electrochemical performance for rechargeable zinc-air battery

The development of highly-efficient bi-functional catalysts for Zn-air battery is of importance for sustainable energy-storage field. Rational utilization the integral advantages of metal-organic frameworks and traditional templates is an effective strategy to achieve high performance multi-functional catalysts. Herein, the di-nuclear Co-Zn-MOF was synthesized on the surface of polystyrene (PS) with a facile method, then the porous N, P co-doped carbon encapsulated Co-based catalysts were developed by calcining the PS@Co-Zn-MOF template followed by acid-mist treatment. The characterization results reveal that acid-mist treatment strategy can efficiently modify the surface feature, and remove the surface-adsorbed and unstable metal nanoparticles, thus improving the stability of catalysts. Moreover, this work also proves that low concentration acid-mist treatment can improve the graphitization degree, while high concentration acid can lead to the increase of defective carbon. With this strategy, the obtained Co@PNC-850-0.1H catalyst achieves an impressive enhanced ORR/OER performance, and the potential difference between ORR and OER is only 0.734 V at 0.1 M KOH condition. Additionally, the Co@PNC-850-0.1H based aqueous and all-solid-state Zn-air batteries (ZABs) also deliver excellent performances with extraordinary power density (194.3 mW·cm−2; 70.7 mW·cm−2), high specific capacity (779.7 mAh·g−1@10 mA·cm−2; 723 mAh·g−1@5 mA·cm−2), and ultra-high stability.

电解老厂房酸雾收集系统改造

分析了锌电解过程酸雾形成机理及同行业的酸雾治理现状，介绍了一种采用冷却塔风机从电解槽底部抽负压的酸雾治理办法，使无组织排放的酸雾有组织收集捕集，达到了较好的酸雾治理效果，实现了作业场所和区域环境的有效改善。 The formation mechanism of acid mist and the present situation of acid mist treatment in the same industry during the electrolytic zinc process were analyzed. An acid mist treatment method, which uses cooling tower fan to take away the subpressure from the bottom of the cell, was introduced. This method can gather the acid mist organically, which discharges without organization, achieving a good effect of acid mist treatment, so as to improve the environment of work sites and the surrounding areas.

BIOMASS, NITROGEN, SULFUR, AND PHOSPHORUS CONTENTS OF BEANS GROWN IN LIMED SOIL IN RESPONSE TO FOLIAR APPLICATION OF HNO3 OR H2SO4 MISTS

Bean plants (Phaseolus vulgaris L.) were subjected to simulated acid mist treatments (pH 4.5, 3.0, 2.3) in the greenhouse. Solutions containing either HNO3 or H2SO4 were applied as mists over a period of 31 days. The growth medium had a pHKCl of 7.9 and a calcium (Ca) content of 18.5 mg g−1. Plants were sampled at flowering and at ripening, for determination of length, fresh and dry weights of different plant organs, and number of nodules. The plant samples were analyzed for nitrogen (N), sulfur (S), and phosphorus (P) content. A significant reduction of stem growth was recorded as a result of the treatment. Some of the plants had interveinal chlorosis, indicating mild iron (Fe) or manganese (Mn) deficiency caused by the high soil pH. The lowest leaflet dry weight was 86% of the control at a dry matter content of 90% of the control. A reduction in shoot:root dry mass ratio was detected. Pod dry weight was not affected. High increases in leaflet N (145%) or S (204%) content were found, which were roughly proportional to the respective treatment levels of HNO3 or H2SO4. Phosphorus content and N:P ratio of leaflets responded to treatment levels and chemical composition of treatment solutions. The root S content was affected only slightly. Nodules were more sensitive to HNO3 treatment, which at pH 2.3 reduced the number of large nodules to 14% of the control at flowering. At ripening of the pods, the effect of treatments on nodules was less pronounced. H2SO4 treatment also reduced the nodule numbers at higher acidities of mist. Nodule numbers at different treatment levels covaried in all variants with stem height growth, shoot:root dry mass ratio and P content in pods. In HNO3 treated plants, the numbers of root nodules changed inversely to the S content in leaflets. It was concluded that an increase in S content in the plants was less than an increase in N content. The hypothesis that H2SO4 mist causes more disturbances in bean plants than HNO3 mist was not confirmed by the current experiments.

Changes in soil phosphatase activity and P transformation rates induced by application of N- and S-containing acid-mist to a forest canopy

The indirect effects of acid-misting applied to tree canopies, on soil P availability, phosphatase activity and P mineralisation rates in a Sitka spruce ( Picea sitchensis (Bong.) Carr) stand have been investigated. The treated trees, grouped according to five height classes, had for four years previously received acid mist consisting of a mixture of H 2SO 4 and NH 4NO 3 (pH 2.5) at concentrations of 3.2 mM H + and 1.6 mM each of NH 4 +, NO 3 − and SO 4 2−. These simulate cloudwater composition in uplands affected by acidic deposition. Another group of mixed height-class trees, received a double dose of acid mist. Control — no acid-misted-trees received only the usual precipitation inputs. The acid mist treatments had previously been found to induce a significant reduction in stem diameter growth, but no canopy visible injury symptoms were observed. Root bioassays had demonstrated the induction of P nutritional stress in acid-misted versus no acid-misted trees. Soil chemical analysis showed that acidifying inputs induced changes in the inorganic P subcycle by: (i) increasing acidity and P sorption capacity of the soils; and (ii) decreasing the concentration of labile inorganic P. We report here on changes in the organic P subcycle (phosphatase activity and gross mineralisation rates). We used a method which applies independent treatments to soil samples (control, HgCl 2-addition, HgCl 2-addition+autoclaving) to separate mineral solubilisation, organic mineralisation and immobilisation of solution P. Soil phosphatase activity was significantly lower under acid-misted trees (263.9 μg pNP h −1 g −1) than under control trees (382.0 μg pNP h −1 g −1). Soils beneath double-dose acid-misted trees showed a 42% reduction in the labile inorganic P pool-size, and a 33% increase in the labile organic P pool-size, compared to soils under control trees. A pattern of decreasing net P solubilisation and gross P mineralisation rates with increasing acid-mist dose-level was also found. Thus, the combined effects of acid-misting on the inorganic and organic P subcycles, in addition to the suggested effect of N saturation enhancing demand for P by the trees, may have induced P deficiency and reduced tree growth. The effects described are considered to be important factors in the forest decline syndrome.

Effects of acid mist and ascorbic acid treatment on the growth, stability of leaf membranes, chlorophyll content and some mineral elements of Carthamus tinctorius, the safflower

Safflower shoots were sprayed with either HNO3,HCl and H2SO4 acid solutions of pH 2.0 ordistilled water as a control and then sprayed with 0and 100 mg L-1 ascorbic acid solutions. In theabsence of ascorbic acid, membranes of leaf discsexcised from acid misted plants were more injured bydehydration (40% polyethylene glycol, P.E.G.) andheat (51 °C) stress than those taken fromunmisted plants. Safflower plants sprayed with HCl andH2SO4 solutions had lower contents ofchlorophyll (Chl.), soluble sugars (S.S.),hydrolysable carbohydrates (H.C.), soluble proteins(S.P.); total free amino acids (T.A.A.) and producedless biomass in their shoot and root systems than theunacidified control. The reverse held true in theplants received HNO3 solution. Proline contentincreased with exposure to an HCl acid mist of pH 2.0.An acid spray of pH 2.0 did not affect shoot Na+,K+ and Mg2+ content but reduced theircontents in the root. Shoot and root Ca2+contents were substantially lower in acid sprayedplants than in the unsprayed analogues. Ascorbic acidtreatment counteracted the deleterious effects of acidmist on the parameters tested, effectively protectingthe plant membranes from dehydration and heat stressinjury. Ascorbic acid protection was more pronouncedin plants that received HCl solution (e.g. chlorophyllcontent was about three-fold higher than that ofascorbic acid untreated analogues) in contrast toeither HNO3 or H2SO4 treated plants.The effects of single factors, acid mist (pH),ascorbic acid (A.A.) and their interaction (pH × A.A)on the parameters tested were statisticallysignificant. The coefficient of determination(η2) indicated that: (1) acid mist (pH) hada dominant role in affecting the stability of leafmembrane to dehydration stress, Chl content, shootlength and dry mass production, shoot S.P. and H.C.,and root S.S., S.P., T.A.A., Ca2+, and Mg2+contents. (2) The effect of ascorbic acid (A.A.) wasdominant for shoot Na+, K+, Ca2+ andproline contents as well as for root H.C. (3) Theshare of pH × AA. interaction was dominant for thestability of leaf membrane to heat stress, root dryweight, shoot S.S., T.A.A. and root Na+ content.(4) The role of pH and A.A. was equally dominant inaffecting root length.

Acid mist and soil Ca and Al alter the mineral nutrition and physiology of red spruce.

We examined the effects and potential interactions of acid mist and soil solution Ca and Al treatments on foliar cation concentrations, membrane-associated Ca (mCa), ion leaching, growth, carbon exchange, and cold tolerance of red spruce (Picea rubens Sarg.) saplings. Soil solution Ca additions increased foliar Ca and Zn concentrations, and increased rates of respiration early in the growing season (July). Soil Al treatment had a broad impact, reducing foliar concentrations of Ca, Mg, Mn, P and Zn, and resulting in smaller stem diameters, sapling heights and shoot lengths compared with soil treatments with no added Al. Aluminum treatment also reduced respiration when shoots were elongating in July and decreased net photosynthesis at the end of the growing season (September). Three lines of evidence suggest that Al-induced alterations in growth and physiology were independent of foliar Ca status: (1) Ca concentrations in foliage of Al-treated saplings were within the range of sufficiency established for red spruce; (2) mCa concentrations were unaffected by Al treatment; and (3) no Al x Ca interactions were detected. Acid mist treatment increased foliar Fe and K concentrations and increased leaching of Ca, Mg, Mn, Zn, Fe, and Al from foliage. Leaching losses of Ca were more than twice those of the element with the next highest amount of leaching (Zn), and probably led to the reductions in mCa concentration and membrane stability of acid-treated saplings. Acidic mist resulted in enhanced shoot growth, and consistent reductions in foliar cold tolerance in the fall and winter. Of the few significant interactions among treatments, most involved the influence of mist pH and Al treatment on foliar nutrition. In general, reductions in cation concentration associated with Al addition were greater for pH 5.0-treated saplings than for pH 3.0-treated saplings. We propose that H(+)-induced leaching of mCa from mesophyll cells is the mechanism underlying acid-induced reductions in foliar cold tolerance of red spruce.

Combined effects of acid mist and frost drought on the water status of young spruce trees ( Picea abies)

This investigation was focused on the effect of frost drought following acid mist exposure on the water status and CO 2 assimilation of young spruce trees ( Picea abies). Trees cultivated in special containers were exposed to acid mist with pH 3 and a control mist with pH 5 for 10 weeks with three mist events per week during autumn. Frost drought, indicating frozen soil with atmospheric conditions allowing transpiration, was simulated in spring for 6 weeks. The controls for frost drought treatments were treatments with humid non-frozen soil. Acid mist application resulted in degradation of the epicuticular needle waxes with melted wax threads and larger lesions in the wax layer. Control needles showed a well-developed epicuticular wax layer. Frost drought inhibited transpiration and CO 2 uptake in both mist treatments almost completely due to stomatal closure. In contrast, trees showed considerable transpiration and CO 2 uptake rates in the treatments with non-frozen soil. Needle water potential of trees (control soil) was normal (−0.60 MPa), whereas water potential in trees of frozen soil was significantly lower, with −1.49 MPa in the control and −2.26 MPa in the acid mist treatment indicating water stress. We suppose from this finding that the deteriorated wax layer impaired the water retention capacity of needles and allowed higher cuticular transpiration compared with the control treatment. Frost drought was associated with a large decrease in starch concentration of needles paralleled by an increase of glucose and fructose concentration, which is suggested to have increased the osmotic potential. This rise in osmotic potential obviously enabled plants of the frost drought treatment+control mist to maintain their turgor which was not different from the turgor of needles from the non-frozen soil treatments. Needles of the frost drought+acid mist treatment, however, had a weak turgor, indicating that in this treatment a strong water stress prevailed. It is suggested that also under natural forest conditions frost drought preceded by acid mist exposure may cause severe forest damage and decline.

Open-top chamber and field exposure of Sitka spruce to simulated acid mist: a comparison of results

Sitka spruce seedlings grown in pots of compost in open-top chambers (OTCs) or outside, in an agricultural loam soil, in different years, were treated with pH 2.5 acid mist comprising an equimolar solution, of H 2SO 4 and NH 4NO 3 at 1.6 mol m −3. The effects of rain, and frequency of acid mist applications on visible injury, nutrition and frost hardiness were evaluated in the OTC experiment. Similar evaluations were undertaken in the field where application frequency was dependent on windspeed, rain and direct sunlight. Rain washing significantly ameliorated the effect of acid mist on frost hardiness in OTCs. In the field experiment there was no effect of acid mist treatment. Increasing the frequency of misting in OTCs for the same exposure exacerbated the detrimental effects of acid mist, causing both visible damage and further increasing the sensitivity of the acid treated trees to freezing temperatures. The results show that the treatment environment can both ameliorate and exacerbate treatment effects.

Exposure to chlorinated acetic acids: Responses of peroxidase and glutathione S-transferase activity in pine needles

During long-term exposure of pine (Pinus sylvestris L.) seedlings to trichloro- and monochloroacetic acids via root uptake or acid mist treatments, both substances were removed from the plant tissues by metabolic activity. None of the treated plants exhibited visible stress symptoms at the concentrations used. In addition, the exposure to both substances led to dramatic changes in the activity of xenobiotic detoxification enzymes (peroxidase and gluthatione S-transferase) in the needles of the plants.

Reduced soil P availability in a Sitka spruce ( Picea sitchensis (Bong.) Carr) plantation induced by applied acid-mist: significance in forest decline

The effects of acid-misting applied to tree canopies, on soil P availability, pH, effective cation exchange capacity and Ca + Mg:Al ratio, plus tree P nutrition in a Sitka spruce ( Picea sitchensis (Bong.) Carr) stand at Glencorse, Scotland have been investigated. The treated trees, grouped according to five height classes, had for four years previously received acid mist consisting of a mixture of H 2SO 4 and NH 4NO 3 (pH 2.5) at concentrations of 3.2 mM H + and 1.6 mM each of NH 4 + NO 3 − and SO 4 2−, with and without soda-glass ballotini, thus simulating cloudwater composition. The treatments were applied approximately twice a week at the equivalent of 2 mm precipitation per treatment from July to December 1990, and throughout the growing season (May–November) in 1991–1992–1993. Another group of mixed height class trees, received a double dose of acid mist at each application. Control trees received only the usual precipitation inputs. The acid mist treatments had been found, reported elsewhere, to induce a significant ( p < 0.05) reduction in stem diameter growth compared to control trees. Acid-mist treatments significantly ( p < 0.01) reduced the water-soluble P content in forest litter as well as the labile inorganic P (resin-extractable) content ( p < 0.05) and phosphate concentrations in equilibrium soil solution ( p < 0.01) in the surface soil, compared to soils under control trees. The labile organic P content ( p < 0.01) and P sorption capacity ( p < 0.01) of the surface soil however were increased compared to soils under control trees. Using a sensitive root bioassay technique, based on the metabolic uptake of 32P, the acid treatment was shown to have significantly ( p < 0.001) increased P stress within the trees, relative to control trees. Acid-mist applied to the tree canopies caused significant ( p < 0.01) decreases in the soil pH, and marked changes in the cation exchange complex composition, though total effective cation exchange capacity of the soil showed little variation. However, base saturation was 90% in soils under control trees but decreased significantly under acid-misted trees and very significantly to less than 30% under trees given the double acid dose treatment. Consequently, the (Ca + Mg):Al ratio was reduced markedly from 9.5 ± 2.9 to 0.4 ± 0.3. The results from this study therefore support the working hypothesis that acidifying inputs induce P deficiency by slowing the cycling of phosphorus and decreasing P availability within the forest ecosystem. The effects are related to the general effects of acidifying inputs on soil pH and base status. The effects described are considered to be important factors in the forest decline syndrome.

Investigation of wet acidic deposition episodes capable of damaging red spruce in the Mt. Mitchell State Park

Cloud events whose wet deposition is comparable to that shown to trigger negative health symptoms in trees constitute environmentally significant episodes of wet deposition. They accounted for approximately one fourth of all cloud events that traversed the Mt. Mitchell State Park, NC, during the summer field seasons of 1986–1988 and 1993. The environmentally significant episodes of wet deposition most frequently occurred during the month of June. The June occurrence is equivalent to the frequency of acid mist treatments shown to initiate health related decline in Red Spruce. The slightly more than three seasons of data were analyzed for a possible relationship between cloudwater acidity, liquid water content, wind speed and wind direction. The data analysis shows: (i) A scatter plot of the liquid water flux versus the H + ion flux differentiates between environmentally significant and non-environmentally significant cloud events of wet deposition. (ii) The synoptic and resulting local wind speed and direction are important in determining whether a cloud event will be environmentally significant or not, since they are related to the origin and the approach of the airflow into the Mt. Mitchell site. (iii) A characteristic 850 mb height field associated with the most frequently occurring environmentally significant cloud only event of wet deposition. Further investigation of wet acidic deposition episodes capable of damaging Red Spruce in the Mt. Mitchell State Park

Stem growth reduction in mature Sitka spruce trees exposed to acid mist

An eighteen-year-old clone of Sitka spruce ( Picea sitchensis (Bong.) Carr) growing in the field was used to evaluate the whole tree response of ‘mature’ Sitka spruce to acid mist treatment. The mist, an equimolar mixture of H 2SO 4 and NH 4NO 3 at pH 2.5 with or without particles (soda glass ballotini < 20 μm diameter), was applied twice weekly (equivalent to 4 mm precipitation week −1) throughout the growing season, May–November 1990–1992. The annual dose of S, N, H applied as mist (at 51, 48 and 3.3 kg ha −1, respectively) was 2.5 times that measured in the Scottish uplands. Throughout the experiment there was no evidence of visible injury symptoms, yet there was a highly significant reduction (p < 0.02) in the stem-area increment relative to the stem area at the start, measured using vernier dendrometer bands. There was no significant difference between the (acid mist + particle) and the acid mist only treatments. The mean relative stem-area increment over two complete growing seasons (1991–1992) was 65% for control trees, but only 53% for acid-misted trees.

Fine Structure of Acid Mist Treated Sitka Spruce Needles: Open-top Chamber and Field Experiments

Sitka spruce grafts (clones DF and 141) grown in open-top chambers (OTC) and ‘mature ’, 6 –8m tall Sitka spruce (clone DF) grown in the field were exposed to acid mist containing an equimolar ion mixture of H 2SO 4and NH 4NO 3at pH2.5. Mist was applied 4 times a week (4 ×1mm) in the OTC experiment and twice a week (2 ×2mm) on average in the field experiment, between May and Oct. 1991. Samples for light and electron microscopy were collected in Nov. and Jan. following acid mist treatment. Acid mist significantly decreased the amount of calcium deposited in the outer epidermal cell walls, the reduction being most pronounced in the OTCs. Ultrastructurally, acid mist caused a significant increase in chloroplast and grana width. Other symptoms associated with acid mist included swelling of chloroplast thylakoids, chloroplast protrusions, cytoplasm vacuolization, increase in large lipid accumulations and sickle-shaped chloroplast thylakoids. In the OTCs, acid mist hastened the acquisition of frost hardening in both clones. In the field, the control trees exhibited more frost injury than the acid mist treated trees suggesting, again, that acid mist had either hastened or enhanced the stage of frost hardiness of treated trees. In general, acid mist induced changes were more pronounced in the OTCs than in the field.

Responses of white clover to gaseous pollutants and acid mist: implications for setting critical levels and loads

summaryWhite clover plants (Trifolium repens L. cv. ‘Grasslands Huia’) were exposed to combinations of gaseous pollutants and acid mists for 15 wk. The treatments were (a) charcoal‐filtered air (control), (b) 40 ppb SO2+ 40 ppb NO2, (e) 40 ppb Oa with additional peaks of 2 × 3 h at 80 ppb and 1 × 1 h at 110 ppb O3 and (d) SO2+NO2+O3 (a combination of treatments b and c), these being combined with acid mist treatments (6 mm wk1) with solutions at pHs of 2.5, 3.5, 4.5 and 5.6. All gaseous pollution treatments resulted in substantial reductions in plant dry weights with additive effects of SO2+ NO2 and O3 in the SO2+ NO2+O2 treatment. There was a lower dry weight, averaged over all gas pollution treatments, for plants exposed to pH 2.5 compared with pH 4.5 or pH 5.6 mists. An interactive effect of gas x mist treatments revealed that effects of acid mists on plant dry weights were overridden by the more toxic O3 and SO2+ NO2+ O3 gas exposures. Net photosynthesis was reduced in plants exposed to pH 2.5 and pH 3.5 mists compared with plants exposed to pH 5.6 mist. Rates of stomatal conductance were reduced by exposure to the gaseous pollution treatments but not to acid mists. Water loss was greater after 55 h for leaves detached from plants exposed to all gaseous pollution treatments compared with ones from control plants. There was a greater loss of water from detached leaves exposed to pH 2.5 compared with pH 5.6 mist. The quantities (loads) of S + N in gaseous form resulting in decreased growth of T. repens were calculated to be much lower than those applied in mists with no adverse effects. It is concluded that the concepts of critical levels and critical loads of pollutants need considerable refinement for realistic assessments of the threat of pollutants to vegetation.

The use of individual tree statistics to quantify effects in an ?acid mist? experiment with mature trees

Mature trees of a single clone of Sitka spruce (Picea sitchensis (Bong.) Carr.) growing in the field were exposed to simulated acid mist at pH 2.5 over three successive years. The growth of each tree in the acid mist treatment, in terms of the stem area increment, was related to the pattern of growth of the untreated trees at the site during 1991 and 1992. In 1993, the effects of stopping the acid mist treatment on half of the treated trees was investigated by comparing the actual growth against that predicted relative to the untreated trees on the basis of the previous years' data. The prediction of growth from one year to the next was consistently too small for the smallest acid-misted trees, suggesting that the growth rates relative to the untreated trees were increasing with time. Relative to the trees which continued to receive acid mist, however, the smaller trees which received no further acid mist in 1993 grew less than predicted, but there was a significantly greater growth than predicted for the largest ‘recovering’ trees. Results from the individual tree modelling approach showed that a 10% change in relative stem area increment would be detectable at the 5% level, using a block of 4 trees as a treatment unit. The statistical techniques used are alternatives to conventional ANOVA calculations in determining statistically significant treatment effects where numbers of replicates are small.

The influence of elevated ozone on freezing tolerance of red spruce seedlings

summaryLaboratory cold‐tolerance assessments were conducted over two seasons on red spruce (Picea rubens Sarg.) seedlings fumigated with various concentrations of ozone (O3) for one or two growing seasons in three independent experiments at three locations. Ozone fumigations were performed at either Boyce Thompson Institute in Ithaca, NY (BTI), the University of Maine in Orono, ME (UMO), or the US Forest Service Research Laboratory in Delaware, OH (USFS). Acid mist treatments of either pH 3.0 or 4.2 were applied in combination with O2 treatments at USFS, Seedlings fumigated with moderate or high concentrations of O3 were never significantly less cold tolerant than seedlings exposed to charcoal‐filtered (CF) air or low O3 concentrations. In fact, there was a tendency for seedlings fumigated with low concentrations of O3 or CF air to be the least cold tolerant. USFS‐fumigated seedlings receiving the lowest O3 concentration (50/0 nl 1−1, day/night concentration) were least cold tolerant on six of the seven sampling dates and significantly less cold tolerant in October and January. In addition, UMO‐fumigated seedlings receiving CF‐air were significantly less cold tolerant in January than those receiving either ambient air (no chamber or non‐filtered treatments) or elevated O3. Acid mist treatments had little influence on the cold tolerance of red spruce seedlings in autumn and early winter, but in January 1990 seedlings exposed to pH 3.0 acid mist were approximately 6 °C less cold tolerant than those receiving pH 4.2. Following the 1988‐89 winter, freezing injury was evident on all seedlings fumigated at BTI, but differences between 3 x ambient O3 and CF treatments were not significant.

Assimilation and stomatal conductance responses of red spruce to midwinter frosts and the constituent ions of acid mist.

Red spruce (Picea rubens Sarg.) seedlings growing outside in open-top chambers were sprayed twice weekly with artificial mists at either pH 2.5 or 5.6, for five months during the 1988 growing season. The mists contained one of the following: water, pH 5.6 (control); (NH(4))(2)SO(4), pH 5.6; NH(4)NO(3), pH 5.6; HNO(3), pH 2.5; H(2)SO(4), pH 2.5; or (NH(4))(2)SO(4) + NH(4)NO(3), pH 2.5. During January 1989, the light responses of assimilation and stomatal conductance were assessed in the laboratory following a 4-day equilibration at 12 degrees C. The aerial portions of the intact trees were then subjected to a mild (-10 degrees C) frost for three hours during the night and the rate of recovery of light-saturated assimilation (A(max)) was determined the following day using the same branches as were used for the assimilation studies before the frost treatment. The same trees were then subjected to a second frost of -18 degrees C for three hours during the following night and the recovery of A(max) of the same branches was measured the next day. All of the acid mist treatments increased A(max) and apparent quantum yield relative to the control treatment when measured before the frost treatments. Frosts of -10 and -18 degrees C resulted in a significant decline in A(max) of seedlings in all treatments except the control. Stomatal conductance increased with increasing irradiance in seedlings in the acid mist treatments that did not contain SO(4) (2-) ion. Stomatal conductance of seedlings in acid mist treatments containing SO(4) (2-) ion was insensitive to changes in irradiance over the range 50-1500 micro mol m(-2) s(-1). It is concluded that acid precipitation increased the sensitivity of the assimilation response to midwinter frosts that follow a brief warm period. The SO(4) (2-) ion appears to be significant in causing increased sensitivity to frost and in causing stomatal insensitivity to light flux density.

Influence of acidic mist on frost hardiness and nutrient concentrations in red spruce seedlings: 2. Effects of misting frequency and rainfall exclusion.

Two-year-old red spruce (Picea rubens Sarg.) of Pittston provenance and 3-yr-old plants of Chatham provenance were exposed to acid mist in replicated open-top chambers supplied with charcoal-filtered air near Edinburgh, Scotland. Plants of Chatham provenance had already been exposed to acid mist throughout the previous growing season. The plants were exposed to mist, equivalent to 4 mm rainfall per week, containing an equimolar mixture of sulphuric acid and ammonium nitrate at pH 2.5 or pH 5.0 (1.6 or 0.01 mol m3 ) from May to November. This weekly dose was delivered at a low frequency (2 mm twice a week), or high frequency (1 mm on 4 consecutive days each week) to chambers fitted with ceilings to exclude rain. The low frequency dose was also applied to chambers without ceilings, to examine the effect of natural washing by rain. Frost hardiness, estimated by exposing detached shoots to controlled freezing and then measuring rates of electrolyte leakage, was determined during the misting period at the end of October and in December. Foliar nutrient concentrations were measured during the dormant period after treatment had ceased. At the end of October, plants which had received acid mist were less frost hardy than plants receiving mist at pH 5. The temperature causing 50% shoot death (LT50 ) increased by 6 °C for low frequency application, and by 10 °C at high frequency, relative to the plants receiving mist at pH 5. Exclusion of ambient rainfall had no detectable effect on the frost hardiness response to acid mist. In December, 3 wk after the cessation of misting, all plants were more frost hardy than in October. Significant effects of the acid mist treatment could no longer be detected. Differences in nutrient concentrations were small among treatments, although K+ concentrations in the low frequency treatment with acid mist with rain exclusion were 50 % below those in other treatments. Ca concentrations were 50% larger in the acid mist treatment with rain exclusion than without. The data suggested enhanced sulphate uptake resulting from increasing the frequency of exposure, but the increase was not significant. There was no clear relationship between the pattern of frost hardiness and nutrient concentrations except for S, which was 30% smaller in the control plants (pH 5) than in the high frequency pH 2.5 treatments. It is concluded that excluding rainfall, an experimental artifact introduced in evaluating effects of acid mist, does not influence the frost hardiness response of red spruce seedlings. The much greater effect of exposure to the same dose at double the frequency suggests that such experiments may underestimate effects in the field, if those trees are exposed to more frequent episodes of polluted cloud water than experimental plants.

Differences in the spectral characteristics of white clover exposed to gaseous pollutants and acid mist

summaryWhite clover plants (Trifolium repens L. cv ‘Grasslands Huia’) were exposed to combinations of gaseous pollutants and acid mists similar to those found in many parts of upland Britain. The gaseous pollutant treatments were (a) charcoal‐filtered air (control), (b) SO2+ NO2 (c) O3 and (d) O3+ SO2+ NO2. The acid mist treatments were 6 mm per week of solutions at pHs of 2.5, 3.5, 4.5 and 5.6. After 12 weeks, canopy reflectance was measured at green, red, near infrared and middle infrared wavelengths using a portable radiometer. Distinct changes in the characteristic spectral reflectance of the clover canopies were noted. The effect of the gaseous pollutants was significant when examined by analysis of variance. The two treatments containing ozone showed particularly marked changes and were statistically separable from the control in a pairwise comparison; the sulphur and nitrogen dioxide treatment was not statistically separable from the control. The acid mists had no significant effect on canopy reflectance. Simple and 4‐waveband vegetation indices showed positive linear relationships with shoot dry weight. The O3+SO2+NO2, in particular, and O3 treatments produced marked decreases in shoot dry weight and vegetation index. The green and near infrared wavebands were the best discriminators of change in canopy reflectance.

Photosynthetic and stomatal conductance responses of Norway spruce and beech to ozone, acid mist and frost—a conceptual model

Two-year-old beech and Norway spruce seedlings were exposed to a combination of ozone and acid mist treatments in open-top chambers in Scotland during the months of July through to September 1988. Replicate pairs of chambers received charcoal-filtered air (control), ozone-enriched air (140 nl ozone litre −1) or 140 nl ozone litre −1 plus a synthetic acid mist (pH 2·5) composed of ammonium nitrate and sulphuric acid. Field measurements of assimilation and stomatal conductance were made during August. In addition, measurements of assimilation and conductance were made during September in the laboratory. Light response curves of assimilation and conductance were determined using a GENSTAT nonrectangular hyperbolic model. During February 1988/9 the Norway spruce were subject to a four day warming period at 12°C and the light response of assimilation determined. The same plants were then subject to a 3-h night-time frost of −10°C. The following day the time-course of the recovery of assimilation was determined. It was found that ozone fumigation did not influence the light response of assimilation of beech trees in the field, although stomatal conductance was reduced in the ozone-fumigated trees. The rate of light-saturated assimilation of Norway spruce was increased by ozone fumigation when measured in the field. Measurements of assimilation of Norway spruce made during the winter showed that prior to rewarming there was no difference in the rate of light-saturated assimilation for control and ozone-fumigated trees. However, the ozone plus acid mist-treated trees exhibited a significantly higher rate. The 4-day period of warming to 12°C increased the rate of light-saturated assimilation in all treatments but only the ozone plus acid mist-treated trees showed a significant increase. Following a 3-h frost to −10°C the control trees exhibited a reduction in the rate of light-saturated assimilation (A max ) to 80% of the pre-frost value. In comparison, following the frost, the ozone-fumigated trees showed an A max of 74% of the pre-frost value. The ozone plus acid mist-treated trees showed an A max of 64% of the pre-frost trees. The time taken for A max to attain 50% of the pre-frost value increased from 30 min (control) to 85 min for ozone-fumigated trees to 190 min (ozone plus acid mist). These results are discussed in relation to the impact of mild, short-term frosts, which are known to occur with greater frequency than extreme, more catastrophic frost events. A simple conceptual framework is proposed to explain the variable results obtained in the literature with respect to the impact of ozone upon tree physiology.