Acid Mist Research Articles

Developments in odour control and waste gas treatment biotechnology: a review

Waste and wastewater treatment processes produce odours, which can cause a nuisance to adjacent populations and contribute significantly to atmospheric pollution. Sulphurous compounds are responsible for acid rain and mist; many organic compounds of industrial origin contribute to airborne public health concerns, as well as environmental problems. Waste gases from industry have traditionally been treated using physicochemical processes, such as scrubbing, adsorption, condensation, and oxidation, however, biological treatment of waste gases has gained support as an effective and economical option in the past few decades. One emergent technique for biological waste gas treatment is the use of existing activated sludge plants as bioscrubbers, thus treating the foul air generated by other process units of the wastewater treatment system on site, with no requirement for additional units or for interruption of wastewater treatment. Limited data are available regarding the performance of activated sludge diffusion of odorous air in spite of numerous positive reports from full-scale applications in North America. This review argues that the information available is insufficient for precise process design and optimization, and simultaneous activated sludge treatment of wastewater and airborne odours could be adopted worldwide.

Effects of Simulated Acid Mist on a Sitka Spruce Forest Approaching Canopy Closure: Significance of Acidified Versus Non-Acidified Nitrogen Inputs

Effects of enhanced N, S and NS Acid additions, up to approximately 100 kg N and S ha−1 y−1, are described for a 15-year-old Sitka spruce forest growing on an acid peat in Scotland. Groups of 10 trees, replicated over 4 blocks, have been treated at canopy height on approximately 50 or 100 occasions with 2 mm precipitation equivalent, between April and November, since 1996. Relative stem volume increment (RSVI) has been consistently higher in the NS Acid treated trees compared with control or N treated trees since the second year of treatment, although no dose response was found. Litterfall was also considerably increased in the NS Acid treatments and showed a clear dose effect but was not correlated with RSVI. Base cation concentrations in soil waters, collected using zero tension lysimeters reflected the presence or absence of the spray treatments and showed a dose related increase in response to NS Acid inputs. Treatment with 2NS Acid increased NH4-N and NO3-N by an order of magnitude. Results after 4 years of treatment showed a positive growth and litterfall response to NS Acid inputs but no effect of N alone. Enhanced stemwood growth may be linked to the higher base cation and phosphate concentrations measured in the soil water in the presence of NS Acid and S treatments.

Spill behaviour using REACTPOOL: Part I. Results for accidental releases of chlorosulphonic acid (HSO 3Cl)

Chlorosulphonic acid is a toxic, highly reactive and corrosive substance that exists in its liquid form at ambient conditions. Its major hazardous potential comes from the clouds of hydrogen chloride and sulphuric acid mist produced whenever this chemical escapes from containment and is exposed to moisture. It decomposes violently and sometimes explosively in the presence of water, liberating heat. On spillage it creates liquid pools that can either boil or evaporate. There are three sources of water available for reaction: free ground water, substrate water and atmospheric moisture. Hydrogen chloride gas or aqueous solution and sulphuric acid liquid are produced by the hydrolysis reaction. This paper describes the dangers involved in cases of accidental releases of chlorosulphonic acid, referring to its properties, toxicity data and mitigation tests. It also reports results of pool behaviour using REACTPOOL [T. Kapias, R.F. Griffiths, C. Stefanidis, J. Haz. Mat., submitted for publication]. These results indicate that the pool behaviour is governed mainly by the amount of water available for reaction. Surface roughness and wind speed also have a significant effect on the results. A discussion of the results in comparison with those for other water reactive substances is presented in Part III of this series of papers [T. Kapias, R.F. Griffiths, J. Haz. Mat., submitted for publication]. The generated cloud will initially contain chlorosulphonic acid, hydrogen chloride and sulphuric acid with numerous processes taking place. Initially, it is usually denser than air. Although chlorosulphonic acid has been involved in major hazard incidents, there are no experimental data relevant to the modelling requirements. Use of REACTPOOL provides insights into the major hazard role of this substance.

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.

Design of complex wire‐mesh mist eliminators

AbstractKnitted wire‐mesh mist eliminators have widespread application in many industrial plants. Despite their extensive use, the open literature regarding them is really limited. Some experimental data and mechanistic models have been published for common knitted wire‐mesh mist eliminators formed from a single metal pad. This type of mist eliminator can be used in most distillation and absorption columns, but because of the poor removal efficiency, cannot be used in operations involving acid mist, fine fog resulting from liquid condensation from a saturated vapor, oil mist from compressed gases, and natural‐gas dehydration applications. Moreover, other possible problems may arise when the separator is fed with high liquid and gas flow rates, because these conditions can induce flooding in the mist eliminator. In both of these cases, common wire‐mesh mist eliminators do not perform satisfactorily, and therefore complex wire‐mesh mist eliminators have to be installed to improve separation efficiency or to increase allowable liquid loadings while avoiding flooding phenomena. This article presents a mechanistic model based on a set of new experimental data obtained by investigating performance of commercial complex eliminators.

Risk of lung cancer in workers producing stainless steel and metallic alloys.

The mortality of workers involved in the production of stainless and alloyed steel from 1968 to 1992 was studied, in order to investigate the risk of lung cancer due to exposure to metals, i.e. iron oxides, chromium and/or nickel compounds. The study design was a historical cohort mortality study and a nested case-control study concerning lung cancer. Standardized mortality ratios (SMRs) were computed using regional mortality rates as an external reference for comparing observed and expected numbers of deaths, adjusting for age, sex and calendar time. Conditional logistic regression was used to estimate odds ratios (ORs). Occupational exposure was assessed through the complete job histories of cases and controls and a specific job-exposure matrix. The cohort comprised 4,288 male and 609 female workers. The observed overall mortality was significantly lower than expected [649 deaths; SMR = 0.91; 95% confidence interval (CI) 0.84-0.98]. No significant SMR was observed for mortality from lung cancer (54 deaths; SMR = 1.19; CI 0.88-1.55). The case-control study was based on 54 cases and 162 individually matched controls. Smoking habits were available for 71%. No lung cancer excess was observed for exposure to (1) metals and/or their compounds, i.e. iron (OR = 0.94, CI 0.48-1.86), chromium and/or nickel (OR = 1.18, CI 0.62-2.25), and cobalt (OR =0.64, CI 0.33-1.25), (2) acid mists (OR = 0.43, CI 0.17-1.10), and (3) asbestos (OR = 1.00, CI 0.54-1.86). With respect to exposure to polycyclic aromatic hydrocarbons (PAHs) and silica, which are often found together in workplaces, (1) high and statistically significant lung cancer excesses were observed, the ORs being 1.95 (CI 1.03-3.72) and 2.47 (CI 1.28-4.77) respectively, (2) quantitative exposure parameters revealed upward trends reaching statistical significance (P < 0.05), and (3) adjustments for tobacco consumption did not reveal any confounding factors from smoking. This study failed to detect any relationship between lung cancer and exposure to iron, chromium, nickel and/or their compounds. High and statistically significant relative risks, along with increasing trends, were observed for simultaneous exposure to PAHs and silica.

What are the causes of a perforated nasal septum?

Perforation of the nasal septum is a clinical condition which occurs due to local trauma, cocaine sniffing, postoperatively (such as after sub-mucous resections) and in association with granulomatous diseases such as Wegeners' granulomatosis. It has also been reported following intranasal steroid therapy. Perforation, proceeded by ulceration, is also a well recognized occupational hazard. Legge reported ulceration and perforation in chrome platers as early as 1902, other occupational causes have been reported such as mercury fulminate, arsenic and cement. Nasal ulceration has also been reported following exposure to ruthenium and platinum salts but it is in chrome platers that the condition has been most closely studied. Hunter described the time interval from first exposure to the development of ulceration and perforation in platers as being between 6-12 months although ulcers have also been reported after only a few days of plating work. The earliest reported time interval between exposure and perforation is just a few weeks. The development of ulceration and perforation is thought to be due to the inhalation of hexavalent chromic acid mist. The mist touches the delicate nasal mucosa at Littles area producing inflammation and erosion/ulceration. This produces symptoms of a sore nose, of actual pain, irritation, rhinorrhoea and nasal bleeding. If exposure is then controlled the ulcer heals with scabbing leaving a permanent scar which is asymptomatic. Continued exposure leads to perforation when the symptoms may cease. Workers with perforations can be asymptomatic and unaware of the 'hole' in their noses but others complain of rhinorrhoea on eating spicy food and of whistling. Rarely psychological disturbance associated with body image can occur. Septal perforations are permanent; surgery maybe undertaken to close the hole and so prevent whistling but surgeons may require that individuals leave the industry before the operation in order to avoid perforation of the implant. The finding of a perforation in the nose of a chrome

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.

Dispersion and thermodynamics of clouds generated from spills of SO 3 and oleum

A new model describing the dispersion behaviour and the processes that occur in a cloud generated from accidental spills of SO 3 and oleum has been developed. Such a cloud may initially behave as a dense gas, with several chemical and physical processes occurring in it. There is not usually enough atmospheric moisture in the air passing immediately above the pool for complete and rapid reaction to sulphuric acid mist. Therefore in the early stages, SO 3 vapour, H 2SO 4 vapour and H 2SO 4 aerosol will be present. At some distance downwind, transition to passive dispersion behaviour will take place and only sulphuric acid aerosol will be present in the cloud. The dense gas model is based on a box type dispersion model. The passive behaviour is described by a Gaussian model that takes into account deposition of the aerosol particles. The model results suggest a number of lines of experimental investigation that are required to provide data for model validation.

The Effect of N Deposition on Nitrous Oxide and Nitric Oxide Emissions from Temperate Forest Soils

Long-term and short-term N deposition effects on N2O and NO emissions from forest soils were compared. Long-term NH3 deposition (> 20 years) from a poultry farm to a downwind woodland (decreasing from 73 to 18 kg N ha−1 y−1, 30 to 110 m downwind of the farm) resulted in the re-emission of 6% and 14% of NH3-N deposited as N2O-N and NO-N, respectively. However, when in short-term (2–3 years) field experiments the atmospheric N deposition to mature conifer plantations was raised by fumigation with NH3 tol5 kg N ha−1 y−1 or by acid mist to 48 and 96 kg N ha−1 y−1 the N deposited was immobilised. In the acid mist experiment more than 2 years of acid mist (48 and 96 kg N ha−1 y−1) were required to significantly increase N2O emissions from −0.3 μg N2O-N m−2 h−1 (control) to 0.5 and 5.7 μg N2O-N m−2 h−1, respectively. This suggests, that N deposition simulation studies in soil ecosystems, which have previously not been exposed to high rates of N (by deposition or fertilisation), need to be long-term. Also, measurements of N2O and/or NO may be a non-destructive, quick indicator of the N status of the soil.

Occupational risk factors for cancer of the gastric cardia. Analysis of death certificates from 24 US states.

We evaluated the risk of gastric cardia cancer by occupation and industry in a case-control study using information from death certificates for 24 US states in 1984-1992. One thousand fifty-six cases of gastric cardia cancer were identified among men aged 20 years or more, including 1,023 whites and 33 blacks. Controls were 5,280 subjects who died of nonmalignant diseases, 5:1 matched to cases by geographic region, race, gender, and 5-year age group. Among white men, occupations with elevated risk included financial managers (odds ratio [OR] = 6.1; 95% confidence interval [CI], 1.3-28.8), janitors and cleaners (OR = 1.7; 95% CI, 1.0-2.9), production inspectors (OR = 3.2; 95% CI, 1.5-6.9), and truck drivers (OR = 1.5; 95% CI, 1.0-2.2). Industries with elevated risk included pulp and paper mills (OR = 2.0; 95% CI, 1.0-37), newspaper publishing and printing (OR = 2.6; 95% CI, 1.0-6.3), industrial and miscellaneous chemicals (OR = 2.0; 95% CI, 1.0-3.9), water supply and irrigation (OR = 5.6; 95% CI, 1.6-19.9). Among black men, risks were nonsignificantly increased for subjects employed in railroads (3 cases, 2 controls) and for carpenters (3 cases, 0 controls). We created job-exposure matrices for asbestos, inorganic dust, metal dust, lead, polycyclic aromatic hydrocarbons, nitrogen oxides, nitrosamines, sulfuric acid, fertilizers, herbicides, other pesticides, and wood dust. Among white men, a consistent pattern of risk increase by level and probability of exposure was observed only for sulfuric acid mists, with a twofold excess (95% CI, 0.6-7.3) associated with high probability of high intensity exposure. A significant 30% increase in risk was observed for those subjects with a high probability of exposure (all levels combined) to lead, and a 60% increase was observed for subjects with high-level exposure to lead (all probabilities combined). However, crosstabulation of gastric cardia cancer risk by probability and level of exposure to lead did not show consistent trends. Asbestos exposure also showed an overall 50% increase but no consistent trends among white men. None of the 12 occupational hazards showed an association with risk for black men.

Some key environmental variables controlling nitrous oxide emissions from agricultural and semi-natural soils in Scotland

Soil N 2O emissions were measured from a range of mineral soils (22 sites) supporting woodlands, grassland and agriculture between 1991 and 1996 and were co-analysed in order to establish some overriding relationships between the N 2O emission and soil temperature, water content, available NH + 4 and NO - 3, pH and N input by fertiliser, manure and atmospheric deposition. Fluxes were measured by chamber techniques. For individual sites, nitrogen, soil temperature and water content were the key variables controlling the emission rates. Nitrogen additions by fertilisation, manure and atmospheric deposition increased the emissions of N 2O. From pasture grazed by sheep 1.7% of the N input from fertiliser and animal excreta was emitted as N 2O. For an experimental sitka spruce plantation receiving acid mist and a mixed woodland in the immediate vicinity of a poultry farm losses of N 2O were estimated at 3.7 and 0.8% of the atmospheric N deposited, respectively. In spite of the large variations in land use, soil physical and chemical characteristics of the 22 data sets collected at different years and at varying frequency, the mean flux from each site could be described by following multiple regression equation: log N 2O ( μg N m -2 h -1)=−1.04+0.165∗soil temperature+0.403∗log N input (kg N ha -1 yr -1) −0.0145∗gravimetric soil water content (% soil dry weight).

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

This research demonstrates that a leaf’s response to acid mist is dependent on the integrity of the leaf cuticle and that significant differences in the structural and physiological disturbances in leaves can be attributable to different types of wind action. Betula pubescens Ehrh. plants were located at adjacent, but contrasting, sites to create different wind treatments: (i) direct wind action, (ii) indirect wind action and (iii) shelter from wind action (control). In combination with the wind treatments, acidic (pHs 5 and 3) or neutral (pH 7) mists were applied weekly. Wind action significantly increased visible leaf injury, microscopic cuticular lesions and cuticular conductance (g c ), but reduced photosynthetic rate (P N ) and stomatal conductance (g s ) compared to shelter. Wind action combined with acid mist was more injurious than wind action alone, but leaves sheltered from wind action were highly resistant to the damaging effects of acid mist. Direct wind action combined with pH 3 mist resulted in the highest values of g c and the greatest number of cuticular lesions. By contrast, indirect wind action combined with pH 3 mist induced most visible injury, but relatively low values of g c and few microscopic cuticular lesions. Acid mist reduced P N only when leaves had been damaged by wind action. Higher values of g c were associated both with increases in the area of visible leaf injury and with the number of cuticular lesions. Compensatory increase in P N of healthy tissue was evident in leaves exposed to combinations of wind action and acid mist.

Practical Slot Hood Design for Acid Mist Control of a Battery Charging Operation

Abstract An enclosed system approach was designed for controlling contaminant generation from a battery plate formation process. Individual design elements were based on practical applications of a variety of parameters common to open surface tank ventilation designs. Beginning with a basic slot/plenum design, improvements such as tank covers with slots and interior baffles to assure equal distribution of the air flow and reduce the capture velocity required for proper control were incorporated. Comparison of exposure levels before and after installation of the system demonstrated that the design increased the capture and control ability of the ventilation system for the same air volume. The system achieved exposure goals and required low air volume without compromising operational requirements.

The response of Norway spruce seedlings to simulated acid mist

Four pot experiments are reported in which Norway spruce (Picea abies (L.) Karst) seedlings, of different nutrient status, were treated with acid mist for one growing season in open‐top chambers (OTCs). Combinations of H+, SO42−, NH4+ and NO3− were applied at different frequencies of application and supplying different doses of S and N kg ha−1. Plant growth, visible injury, frost hardiness and nutrient status were observed. These experiments were undertaken to improve our understanding of the interaction of environmental factors such as nutrition and mist‐exposure frequency on seedling response to N and S deposition.Both acidity (pH 2·7) and SO42− ions were necessary to induce visible injury. Mist containing SO42−, H+ and to a lesser extent NH4+ significantly reduced winter frost hardiness. Increasing the misting frequency, and to a lesser extent the overall dose, increased the likelihood of acid mist causing visible injury and reducing frost hardiness. Post‐planting stress, low N status and needle juvenility increased the likelihood of acid mist causing visible injury. Increased plant vitality, adequate N status and growth rate reduced the likelihood of acid‐mist‐induced reductions in frost hardiness.Principles underlying the responses of spruce seedlings treated in controlled conditions to acid mist are discussed.

Lung cancer mortality in nickel/chromium platers, 1946-95.

OBJECTIVES: To investigate mortality from lung cancer in nickel/chromium platers. METHODS: The mortality experience of a cohort of 1762 chrome workers (812 men, 950 women) from a large electroplating and...

Assessment of the Health Hazard Associated with the Use of Smoke Tubes in Healthcare Facilities

Abstract Of particular concern to facilities engineers and healthcare workers is the evaluation of air flow patterns in or near a respiratory isolation room and negative pressure. The Centers for Disease Control and Prevention recommended the use of smoke tubes for this purpose in the second edition of Guidelines for Preventing the Transmission of Mycobacterium tuberculosis in Health-Care Facilities, 1994. This article provides an assessment of the potential for patient and healthcare worker exposure to hazardous levels of acid mist when smoke tubes are used to monitor negative pressure. Three brands of smoke tubes (Sensidyne, MSA, and Drager) were initially investigated. In a bench-top experiment, air was pushed in 30-ml increments through a smoke tube and into 10 ml of deionized water in a scintillation vial. The hydrogen ion concentration of the solution was measured and the generation rate of acid mist was estimated to be 3.3 mg per 30-ml squeeze. The quantity of hydrochloric acid (9.8 mg) from three ...

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.

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

Acid mist (pH 3) precipitation led to a degradation of the epicuticular waxes of the youngest needles. Under the influence of frost drought in spring those affected trees resulted in a detrimental decline in needle water potential and turgor potential. The results indicate that a damaged, poor cuticle loweres the water retention capability and increases water losses by non stomatal, cuticular transpiration. Therefore acid mist treated trees seem to be more endangered to water stress under frost drought conditions in spring than trees with an intact cuticula. The results are in agreement with observations of decline symptoms under field conditions after years of drought. The influence of mist acidity in combination with frost simulatio during winter time were of minor importance.