Acid Mist Research Articles

Soil nitrous oxide and nitric oxide emissions as indicators of elevated atmospheric N deposition rates in seminatural ecosystems

Elevated N deposition caused by ammonia emissions from poultry and pig farms, and supplemented N concentrations in acid mist in field and chamber experiments increased soil available NH 4 + and NO 3 − concentrations and emissions of N 2O and NO. In a ‘pristine’ soil, not previously exposed to high N deposition rates, an initial threshold of 40 kg N ha −1 year −1 was required to increase N 2O emissions. For all data described here on average 0.76% (range 0.2 to 15%) of the elevated N deposited was emitted as N 2O. For soils exposed to long-term and large N deposition rates N 2O losses >3% of the N deposition rate were calculated. This suggests that N 2O losses of more than 3% of the N input can be indicative of soil ecosystems where the N input exceeds its demand. For NO a more limited data set showed losses ranging from 1.3 to 20% of the elevated N input. It was calculated that NH 3 emissions from all intensive pig and poultry farms in Great Britain accounted for 18 t N 2ON year −1 and that poultry farms accounted for less than 3 t NON year −1.

Response of leaf surfaces and gas exchange to wind stress and acid mist in birch (

Response of leaf surfaces and gas exchange to wind stress and acid mist in birch (

Air Sampling Methodologies for Sulfuric Acid Mist in Copper Electrowinning: Field Evaluation and Development of a New Method

Abstract Assessment of the options for the sampling and analysis of sulfuric acid mist in the copper electrowinning tankhouse environments suggests a new method that addresses the sulfate interference problem inherent in these operations. Currently available analytical methods such as the Occupational Safety and Health Administration Analytical Method ID-113 and National Institute for Occupational Safety and Health Analytical Method 7903 produce statistically dissimilar results when evaluated simultaneously in a tankhouse environment. Neither method provides a basis to differentiate the sulfate bound in sulfuric acid mist from that found in salts such as copper sulfate. Owing to these problems and the need for accurate exposure assessment data for sulfuric acid mist, a new air sampling and analysis method was developed using a polypropylene filter with extraction in anhydrous isopropyl alcohol. Sulfuric acid is highly soluble in anhydrous isopropyl alcohol in contrast to the majority of the primary sulfat...

Field application of acid mist to a single clone of sitka spruce: effects on foliar nutrition and frost hardiness

Trees (>2.5 m tall) belonging to a single clone of physiologically mature Sitka spruce ( Picea sitchensis (Bong.) Carr), growing in a base rich agricultural loam, were treated approximately twice weekly with acid mist (pH 2.5) over three consecutive growing seasons. The treatment consisted of acid mist containing H +, NH 4 +, NO 3 − and SO 4 2− in equimolar concentrations (1.6 mol m −3) identical to that used in previous open-top chamber (OTC) studies with seedlings and grafted cuttings. The acid mist supplied approximately 48 kg N and 51 kg S ha −1 year −1 and 3.3 kg H ha −1 year −1. Treated trees were surrounded by a framework which supported temporary blinds, positioned only during the spray treatment. Control trees received no treatment. Groups of four trees were assigned to one of five height classes, to take account of a gradient in height across the site, and these groups were treated as units of replication. Shoot frost hardiness and foliar nutrient concentrations were measured for comparison with previous OTC studies. Tree size, which initially was positively correlated with differences in nutrient status (N, P, S and K), exerted a significant effect on the frost hardiness response to acid mist. Acid mist had a negative effect on frost hardiness only in the smallest trees, and only when the trees were already hardy to −20°C and treatment applications were regular and continuous up to sampling. There was no evidence of foliar mediated effects such as enhanced ion leakage rates and substantially elevated foliar S concentrations which typified OTC exposures. The usefulness of these variables with respect to monitoring field effects of acid mist is discussed together with the importance of different environmental factors which appear to control tree response in the field.

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.

Soil dressing with sulphur: does it reduce frost hardiness in spruce seedlings?

This experiment was undertaken to quantify the effects of root absorbed SO 2− 4 on frost hardiness, an indicator of physiological perturbation. Experiments with acid mist suggest that the root mediated pathway for SO 2− 4 uptake exerts a relatively small detrimental effect on frost hardiness. Bare-root transplants of Sitka and red spruce seedlings were grown outdoors for one growing season, in compost top dressed with different fertilizer treatments, with or without SO 2− 4. Without SO 2− 4: Vitax Q 4, KNO 3 and NH 4H 2PO 4. With SO 2− 4: K 2SO 4, (KNO 3 + K 2SO 4) and (NH 4H 2PO 4 + K 2SO 4). These treatments supplied upwards of the equivalent of 71 kg N ha −1 and 98 kg S ha −1. At the end of the growing season, frost hardiness was measured on detached shoots, frozen in a purpose-built freezing cabinet and assessed for damage, indicated by the rate of electrolyte leakage from the frozen tissue. Soil top dressing with SO 2− 4 did not significantly enhance rates of electrolyte leakage from frozen shoots of either Sitka or red spruce, even at S dose rates exceeding (by a factor of at least 4), those likely to be supplied as acidic deposition. Reductions in frost hardiness were observed where SO 2− 4 was added, but these effects were not significant confirming that foliar uptake of S is necessary for the significant reductions in frost hardiness caused by acid mist.

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

Laryngeal cancer incidence among workers exposed to acid mists (United States).

In 1992, the International Agency for Research on Cancer (IARC) determined that sufficient evidence existed to classify sulfuric acid mists as a human carcinogen, based primarily on six human studies. Possible mechanisms include irritation of epithelial cells in conjunction with cigarette smoking, or a direct genotoxic effect due to a modification of cellular pH. We have followed 1,031 men exposed to acid mists in the steel industry in the United States, via mailed questionnaire and telephone interview, extending by 10 years a prior follow-up of this cohort. These workers averaged 9.2 years of exposure, with an average first year of exposure of 1949. The primary exposure was to sulfuric acid mist, although part of the cohort was exposed to other acid mists. Fourteen laryngeal cancers were observed in the cohort compared with 5.6 expected based on US rates, with follow-up through 1994. A 14 percent upward adjustment in expected cancers due to differences in tobacco and alcohol consumption led to 6.4 laryngeal cancers expected, yielding a rate ratio of 2.2 (95 percent confidence interval = 1.2-3.7). Our findings are consistent with previous findings from this cohort and from most other studies, and tend to confirm IARC's classification of acid mists as a human carcinogen. The occupational exposures of this cohort were at least an order of magnitude higher than usual ambient exposures in urban air.

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.

Effects of Ultraviolet-B Radiation and Acid Mist on Growth and Leaf Wettability o Radish Plants

Radish plants were grown in chambers (PPFD 300μmol m-2 s-1, day length 14h, 21°C, 70%RH) for 10 days, under UV-B irradiation (UV-BBE; 0, 6.5 (low) and 8.6 (high) kJ m-2 d-1) for 12h a day; the plants were exposed to acid mist (pH 3.0 and 5.6) every 2 days. At the end of the treatments, leaf area, dry weights of shoot and hypocotyl, total chlorophyll content, water loss rate and water droplet contact angle (DCA), which is a measure of wettability, on adaxial and abaxial leaf surfaces were determined in each of 9 combinations of treatments, 3 (UV-B)×3 (mist, including no mist). UV-B radiation significantly decreased leaf area and dry weights of shoot and hypocotyl, and increased total chlorophyll content per unit leaf area. Similarly, acid mist of pH 3.0 significantly decreased leaf area and hypocotyl dry weight. However, no combined effect of UV-B and mist on these growth parameters and chlorophyll content was found. On the other hand, there were significant combined effects on DCA on both adaxial and abaxial surfaces; at the high UV-B level, DCA on adaxial surfaces of treated leaves with mist decreased, although that of untreated leaves increased.

A Review of the Chronic Toxicity, Carcinogenicity, and Possible Mechanisms of Action of Inorganic Acid Mists in Animals

Occupational exposure to inorganic acid mists containing sulfuric acid has been associated with increased laryngeal cancer. The primary objective of this review was to compile the literature regarding chronic toxicity and carcinogenicity of inorganic acid mists in laboratory animals. Several chronic toxicity studies had exposures of 1 year or longer. Whereas numbers of animals were limited, no evidence of neoplastic or preneoplastic lesions was reported. Two studies evaluated the carcinogenicity of inorganic acid mists in rats; however, one was limited by a short duration of exposure and the other did not achieve a maximum tolerated dose. A large lifetime study in hamsters evaluated the carcinogenicity of 100 mg/M3 sulfuric acid mist, as well as its ability to act as a promoter or co-carcinogen for benzo(a)pyrene. No evidence of carcinogenic potential was shown. Although an increase in papillomas was noted in the benzo(a)pyrene + H2SO4 group, the co-carcinogenic or promoting potential was considered equivocal. Thus, no evidence from experimental animals strongly supports or refutes the induction of cancer by inorganic acid mists. A possible mechanism that could be associated with inorganic acid mist carcinogenicity relates to the genetic consequences of lowering the pH. Reduced pH can induce chromosomal aberrations, enhance depurination, and deamination of cytidine in DNA. This mechanism has not been evaluated in tissues of the respiratory tract.

An updated mortality follow‐up study of Florida phosphate industry workers

We have added 14 years of mortality follow-up to a previously studied cohort of 18,446 white and 4,546 nonwhite male workers in the Florida phosphate industry. Follow-up was performed for the years 1949–1992. Based on comparisons with national rates, lung cancer standardized mortality ratios (SMR) were slightly elevated among white (SMR = 1.19; 354 observed) and nonwhite males (SMR = 1.13; 105 observed). However, no lung cancer excesses were found relative to local county rates (SMR = 0.98 for whites, SMR = 0.94 for nonwhites). Based on internal analyses of lung cancer mortality, using Poisson regression modeling, there were no associations of lung cancer with cumulative exposures to total dust, silica, or acid mists. There were weak trends or lung cancer risk with alpha and gamma radiation among white males, but no associations with radiation in nonwhites. No relation was found between acid mist exposures and laryngeal cancer. We conclude that there have not been large excesses of lung cancer or other diseases related to workplace exposures in this cohort. © 1996 Wiley-Liss, Inc.

Effects of elevated CO2, O3 and K deficiency on Norway spruce (Picea abies): nutrient supply, content and leaching

summaryTwo clones of 5‐yr‐old Norway spruce (Picea abies [L.] Karst.) were exposed to two atmospheric concentrations of CO2 (350 and 750μmol mol−1) and of O3 (20 and 75 nmol mol−1) in a phytotron at the GSF‐Forschungszentrum (Munich) over the course of a single season (April‐October). The phytotron was programmed to recreate an artificial climate similar to that at a high elevation site in the Inner Bavarian forest, and trees were grown in 40 1 containers of soil (pH 3.5) fertilized to achieve two levels of potassium nutrition; well fertilized and K‐deficient. Foliar nutrient analyses performed at the beginning of the exposure indicated that the fertilization programmes achieved their goal without significantly altering the levels of other nutrients or the soil pH. At the beginning of the fumigation, foliar K concentrations were 7–9 mg g−1d. wt for well fertilized trees and 4–5 mg g−1 d. wt for trees receiving no supplemental K. Over the course of the season, differences between K treatments intensified so that by the end of the experiment there was a five to sixfold difference between foliar K concentrations. This was associated with slight, but significant (P &lt; 0.05), decreases in S and Zn (and of Cu in the 1989 needle year age class) and higher levels of C, N and Mg in K‐deficient trees. Foliar N concentrations were low for all trees (9–15 mg g−1needle d. wt) but were similar to levels found in the field.Elevated O3 was found to decrease significantly the C (P &lt; 0.05) and N (P &lt; 0.001) content of both current‐year (1989) and previous‐year (1988) needles independent of CO2 concentration, but apart from some minor changes in the concentrations of Cu and Mn in the current‐year needles no other effects of the pollutant on plant nutrient status were found. In contrast, CO2 enrichment resulted in significantly (P &lt; 0.01) lower concentrations of K and P (effects on Mg were also on the borderlines of statistical significance) in current‐year needles, but there was no influence on the nutrient composition of the previous‐year needles (although effects on N were on the borderlines of statistical significance). CO2 enrichment also increased (P &lt; 0.05) the C:N ratio of both current‐year and previous‐year needles. One factor contributing to the decline in foliar K at elevated CO2 appeared to be a marked increase (25–30%) in the rate at which cations were leached from the canopy by repeated simulated acid mist (pH 4.0) events, and this effect occurred independently of the O3 concentration. The information presented will aid the interpretation of parallel studies examining the effects of elevated CO2 and/or O3 on seasonal changes in photosynthesis, non‐structural carbohydrate content, antioxidants, tree growth and water use efficiency, and sheds further light on the growing scepticism concerning the role of O3 in the development of Mg and K‐deficiency symptoms characteristic of certain types of forest decline in central Europe.

Clinical and histopathological changes of the nasal mucosa induced by sulfuric acid mists

Clinical and histopathological changes of the nasal mucosa induced by sulfuric acid mists

Upper aerodigestive cancer in battery manufacturers and steel workers exposed to mineral acid mists.

To assess the risk of cancer from inhalation of mineral acid mists. A cohort study and nested case-control study of upper aerodigestive tumours were carried out in men employed since 1950 at two battery plants and two steel works in Britain. The cohort was identified from personnel records and included 2678 men with definite exposure to acid mists (mainly sulphuric acid), 367 with possible exposure, and 1356 who were unexposed. Mortality was compared with that in the national population by the person-years method. Cases of upper aerodigestive cancer were identified from death certificates and cancer registrations, and their exposure to acids was compared with that of age matched controls (five per case) from the same plant by conditional logistic regression. In follow up to 31 December 1993, 93% of men were traced, including 1277 who had died. Among the men definitely exposed to acid mists, overall mortality was less than in the national population (standardised mortality ratio (SMR) 0.92, 95% confidence interval (95% CI) 0.85-0.98) as was mortality from all cancers (SMR 0.92, 95% CI 0.79-1.05) and specifically from cancer of the larynx (SMR 0.48, 95% CI 0.01-2.70) and lung (SMR 0.98, 95% CI 0.78-1.22). A total of 15 incident or fatal cases of upper aerodigestive cancer were identified during follow up. When these men were compared with controls, risk was moderately increased in those who had worked for at least five years in jobs entailing exposures to sulphuric or hydrochloric acid in excess of 1 mg/m3 (OR 2.0, 95% CI 0.4-10). These findings are consistent with those from other studies which have indicated a hazard of upper aerodigestive cancer from acid mists. However, they indicate that any risk from exposures to sulphuric and hydrochloric acid below 1 mg/m3 is small.

Interactive effects of gaseous air pollutants and acid mist on two major pasture grasses

Plants of Lolium perenne L. (perennial ryegrass) and Agrostis capillaris L. (common bent-grass) were exposed, for 18 and 22 weeks respectively, to combinations of gaseous pollutants and acid mists. The gaseous pollutant treatments were (a) charcoal filtered air, (b) 40 ppb SO 2 + 40 ppb NO 2, (c) 40 ppb O 3 with additional peaks of 2 × 3 h at 80 ppb and 1 × 1 h at 110 ppb O 3 and (d) SO 2 + NO 2 + O 3 (a combination of treatments (b) and (c)) and the mist treatments were 6 mm per week of solutions at pH 2.5, 3.5, 4.5 and 5.6. All gaseous pollution treatments resulted in substantial reductions in the dry weights of plants of L. perenne but there were less than additive effects of O 3 and SO 2 + NO 2 in the SO 2 + NO 2 + O 3 treatment. There was a stimulation in the growth of L. perenne exposed to pH 2.5 compared with less acid mists in the charcoal filtered air and O 3, but not in the SO 2 + NO 2 and SO 2 + NO 2 + O 3, gas treatments. Plants of A. capillaris were more resistant to the gas × mist treatments. There were no significant differences ( P ≤ 0.05) in the weights of total shoots for plants grown in the gas exposure treatments compared with those grown in charcoal-filtered air. There was a growth stimulation for plants of A. capillaris exposed to pH 2.5, compared with less acid mists, in all gas treatments. For both species, all gaseous pollution treatments caused a reduction in green shoots and an increase in dead ones. The data are discussed in relation to critical levels and loads of pollutants. It is concluded that these concepts need some refinement for assessing the threat of pollutants to vegetation.

Uptake of ammonium and nitrate ions from acid mist applied to Sitka spruce [Picea sitchensis (Bong.) Carr.] grafts over the course of one growing season

Cloned Sitka spruce grafts were subjected to NH4NO3 mist (1 mm day-1 equivalent) acidified with H2SO4, for 4 days a week, from April until November. Three N treatments at pH 5.0 used 0.01 mol m-315NH415NH3, 1.6 mol m-315NH4 NO3 or 1.6 mol m-3 NH415NO3. At pH 2.5, the treatments were15NH415NO3,15NH4NO3 and NH415NO3 all at 1.6 mol m-3. At the end of the growing season,15N was found in every part of the trees, even when NH4NO3 was supplied at 0.01 mol m-3. It was shown that both\(NH_{4^ + } \) and\(NO_{3^ - } \) could enter needles to a similar degree and be transported to the roots. No differences between pH treatments or clones could be demonstrated. Entry of labelled N via the roots, in those trees with unprotected compost, was reflected in higher fine root15N content, but no change in shoot15N levels. Per cent incorporation expressed as labelled N as a percentage of total N, was generally at its highest in bark, and in older needles in all treatments, values ranging from 5 to 11%. When15N content was expressed as total content for each tree part on a per tree basis, 25–36% was found in current year needles, with a further 12% in current year bark. The most reproducible data was that for dry weight of tree parts as per cent of the whole tree, where proportions compared closely between treatments and the two clones used. The implications of the results for cuticular transport mechanisms, N storage and internal cycling are discussed.

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.