Chemical Composition of Acid Fog

Observational study of microphysical and chemical characteristics of size-resolved fog in different regional backgrounds in China

To investigate the relationship between microphysical and chemical characteristics of size-resolved fog droplets in different regional backgrounds, we conducted observational experiments in urban, mountainous, rainforest, and rural areas of China. Fog water samples across different diameter ranges (4-16 μm, 16-22 μm, and >22 μm) were collected, alongside fog droplet spectra data. Our findings reveal a close relationship between pH value, electrical conductivity (EC), total ion concentration (TIC) of droplets, and droplet sizes, with smaller droplets exhibiting stronger acidity and higher ion concentrations. Significant differences in chemical composition are observed across size ranges and regional backgrounds. Droplet number concentration (N) and liquid water content (LWC) distributions in different regional backgrounds are skewed, with peak diameters of LWC spectra similar to those of N spectra, yet overall spectral distributions varied significantly. Droplet number concentrations are highest in urban area, while large droplets contribute more to overall LWC in mountainous, rainforest, and rural areas. No direct evidence linked LWC or surface area (S) to LWC ratio to water-soluble ion concentrations of size-resolved fog droplets in different regional backgrounds. However, by adjusting the contributions of S and LWC proportions of different-sized droplets to the ion concentration proportions, we find that expanding the LWC proportion to 2.43 times and decreasing the S proportion to 0.2 times for large droplets, while decreasing the LWC ratio to 0.76 times for small droplets, provided a better explanation for the distribution of ion concentrations. This study advances our understanding of the intricate relationship between the microphysical and chemical characteristics of fog, helping to develop more robust and comprehensive models for fog prediction and management.

Geochemical studies of low molecular weight organic acids in the atmosphere: sources, formation pathways, and gas/particle partitioning

Low molecular weight monocarboxylic acids (LMW monoacids, C₁-C₁₀) are the most abundant gaseous organic compound class in the atmosphere. Formic or acetic acid is the dominant volatile organic compound (VOC) in Earth's atmosphere. They can largely contribute to rainwater acidity, especially in the tropical forest, and react with alkaline metals, ammonia, and amines, contributing to new particle formation and secondary organic aerosol production. Gaseous and particulate LMW monoacids were abundantly reported in China. They can be directly emitted from fossil fuel combustion and biomass burring; however, the secondary formation is more important than primary emissions via the photochemical oxidation of anthropogenic and biogenic VOCs. In this paper, we review the distributions of LMW monoacids from urban, mountain, and marine sites as well as from rainwater and alpine snow samples and discuss their sources and formation mechanisms in the atmosphere. We also discuss their importance as cloud condensation nuclei (CCN) and provide future perspectives of LMW monoacids study in the warming world.

A Champion for Chemistry: Elements of Jim Morgan's Intellectual Legacy

James (Jim) Morgan was a leading figure in the field of environmental science and engineering. He championed the application of chemistry in the study of the environment and the design and optimization of environmental treatment processes. Jim influenced the field through his classic text Aquatic Chemistry, coauthored with Werner Stumm, his role as founding editor of Environmental Science& Technology, his seminal contribution to computational methods for the calculation of chemical equilibria, and most especially, his mentorship of his extended academic family. Jim transmitted his enthusiasm for research, particularly on the chemistry of manganese and iron, so successfully to his doctoral students and postdoctoral advisees that many of them carried these topics forward in their own careers.

The Atmosphere

The atmosphere is composed of nitrogen, oxygen and argon, a variety of trace gases, and particles or aerosols from a variety of sources. Reactive, trace gases have short mean residence time in the atmosphere and large spatial and temporal variations in concentration. Many trace gases are removed by reaction with hydroxyl radical and deposition in rainfall or dryfall at the Earth's surface. The upper atmosphere, the stratosphere, contains ozone that screens ultraviolet light from the Earth's surface. Chlorofluorocarbons released by humans lead to the loss of stratospheric ozone, which might eventually render the Earth's land surface uninhabitable. Changes in the composition of the atmosphere, especially rising concentrations of CO₂, CH₄, and N₂O, will lead to climatic changes over much of the Earth's surface.

Chemical compositions of fog and precipitation at Sejila Mountain in the southeast Tibetan Plateau, China

Chemical compositions of fog and rain water were measured between July 2017 and September 2018 at Sejila Mountain, southeast Tibet, where fog events frequently occurred in original fir forests at altitude 3950 m. Fog water samples were collected using a Caltech Active Strand Cloud Collector (CASCC), and rain samples were collected using a precipitation gauge. Differences were observed between fog water and rain composition for most analyzed ions. Ion abundance in fog water was Ca²⁺ > Cl^- > Na⁺ > SO₄^2- > Mg²⁺ > NH₄⁺ >K⁺ > NO₃^- whereas an order of Ca²⁺ > Na⁺ > Cl^- > Mg²⁺ > SO₄^2- > NO₃^- > K⁺ > NH₄⁺ was observed for rain water. All ion concentrations were higher in fog water than in rain water. Additionally, Ca²⁺ was the dominant cation in both fog and rain samples, accounting for more than half of all measured cations. NH₄⁺ and SO₄^2- concentrations were notable for being higher in fog than rain water when compared with other ions. For trace elements, Al, As, Mn and Se were the most abundant elements in fog water; only Al and As were detected in rain water. Seventy-two hour back-trajectory analysis showed that air masses during fog and/or rain events mainly came from the south of Sejila Mountain. Spearman correlation analysis and source contribution calculations indicated that both marine and terrestrial sources contributed to the observed ion concentrations. Considering the higher concentrations of NH₄⁺ and higher ratio of NH₄⁺/NO₃^- measured in fog than in rain, we suggest that quantification of fog nitrogen deposition and its ecological effect in this area should be given more attention.

Chemical Wastes in our Atmosphere—An Ecological Crisis

A large variety of chemical wastes is added to our atmosphere from nu merous human activites. Some of these, such as sulfur and nitrogen oxides (which produce acid rain), ozone, metals, and hydrocarbons, have reached high concentrations in industrialized and urbanized regions of the globe and are causing an ecological crisis.

Acid rain and snow have been falling on increasingly widespread areas of the world during the past several decades. Large areas of North America, Europe, and Asia now receive rain that is, on average, 10 to greater than 30 times more acidic than would be expected for unpolluted atmospheres. Fre quently, individual rainstorms or cloudwater events have pH values of less than 3. Dry deposition of acidic substances (gases and particles) to natural ecosystems may equal inputs from rain and snow.

Effects of air pollution on surface waters, forests, and crops are very difficult to quantify because these natural systems are exceedingly variable and complex. Nevertheless, thousands of lakes and streams in North America and Europe have become so acidic that they cannot support viable populations of fish and other organisms. Highly acidic precipitation events coupled with high atmospheric concentrations of ozone and metals can cause plant damage. Crop loss from ozone damage in the United States is estimated at 6 to 7% annually. The environmental and economic conse quences of air pollution have yet to be evaluated fully, but atmospheric ozone and inputs of acids and metals to terrestrial and aquatic ecosystems clearly represent a potential ecological crisis.

Various historical and transboundary aspects of these air pollution problems have become controversial political and economic issues, particu larly between states within the United States, between the United States and Canada, and between various countries in Europe. The solution to this many-faceted environmental problem represents an enormous scientific and political challenge.

Protonation and oligomerization of gaseous isoprene on mildly acidic surfaces: implications for atmospheric chemistry

In a global process linking the Earth's climate with its ecosystems, massive photosynthetic isoprene (ISOP) emissions are converted to light-scattering haze. This phenomenon is imperfectly captured by atmospheric chemistry models: predicted ISOP emissions atop forest canopies would deplete the oxidizing capacity of the overhead atmosphere, at variance with field observations. Here we address this key issue in novel laboratory experiments where we apply electrospray mass spectrometry to detect online the products of the reactive uptake of gaseous ISOP on the surface of aqueous jets as a function of acidity. We found that ISOP is already protonated to ISOPH(+) and undergoes cationic oligomerization to (ISOP)(2)H(+) and (ISOP)(3)H(+) on the surface of pH < 4 water jets. We estimate uptake coefficients, γ(ISOP) = (0.5 - 2.0) × 10(-6) on pH = 3 water, which translate into the significant reuptake of leaf-level ISOP emissions in typical (surface-to-volume ∼5 m(-1)) forests during realistic (a few minutes) in-canopy residence times. Our findings may also account for the rapid decay of ISOP in forests after sunset and help bring the global budget of volatile organic compounds closer to balance.

Metals in air pollution particles decrease whole-blood coagulation time

The mechanism underlying procoagulative effects of air pollution particle exposure is not known. The authors tested the postulate that (1) the water-soluble components of an air pollution particle could affect whole-blood coagulation time and (2) metals included in this fraction were responsible for this effect. Exposure to the water-soluble fraction of particulate matter (PM), at doses as low as 50 ng/ml original particle, significantly diminished the whole-blood coagulation time. Inclusion of deferoxamine prolonged coagulation time following the exposures to the water-soluble fraction, whereas equivalent doses of ferroxamine had no effect. Except for nickel, all metal sulfates shortened the whole-blood coagulation time. Iron and zinc were two metals with the greatest capacity to reduce the coagulation time, with an effect observed at 10 ng/ml. Finally, in contrast to the anticoagulants citrate and EDTA, their iron complexes were found to be procoagulative. The authors conclude that metals in the water-soluble fraction of air pollution particles decrease whole-blood coagulation time. These metals can potentially contribute to procoagulative effects observed following human exposures to air pollution particles.

Fog and precipitation chemistry at a mid-land forest in central Taiwan

We analyzed fog and bulk precipitation chemistry at a cloud forest in central Taiwan where mountain agriculture activities are highest. There were 320 foggy days (visibility <1000 m) recorded between April 2005 and March 2006. Fog was most frequent between April 2005 and July 2005 and in March 2006 (153/153 d) and least frequent in January 2006 (21/31 d). The total fog duration was 2415 h, representing 28% of the sampling period. Compared with bulk precipitation, fog was disproportionally enriched in NO(3)(-) and SO(4)(2-) relative to K(+), Ca(2+), Mg(2+), and NH(4)(+), resulting in higher a content of nitric acid and sulfuric acid than weak acids or neutral salts and, therefore, higher acidity (median pH, 4.9) in fog than in bulk precipitation (median and mean pH, 5.5). The very high input of NH(4)(+) (47 kg N ha(-1) yr(-1)) through bulk precipitation suggests that the use of fertilizer (ammonium sulfate and animal manure) associated with mountain agriculture has a major impact on atmospheric deposition at the surrounding forest ecosystems. The input of inorganic N reached 125 kg N ha(-1) yr(-1) and likely exceeded the biological demand of the forest ecosystem. Sulfate is the most abundant anion in fog at Chi-tou and in precipitation at various forests throughout Taiwan, suggesting that the emission and transport of large quantities of SO(2,) the precursor of SO(4)(2-), is an island-wide environmental issue.

Chemistry of fogs at Agra, India: influence of soil particulates and atmospheric gases

Fog water samples were collected in the months of December and January during 1998-2000 at Agra, India. The samples were analyzed for pH, major anions (F(-), Cl(-), SO(4) (2-), NO(3) (-), HCOO(-) and CH(3)COO(-)), major cations (Ca(2+), Mg(2+), Na(+) and K(+)) and NH(4) (+) using ion chromatography, ICP-AES and spectrophotometer methods, respectively. pH of fog water samples ranged between 7.0 and 7.6 with a volume weighted mean of 7.2, indicating its alkaline characteristic. NH(4) (+) contributed 40%, SO(4) (2-) and NO(3) (-) accounted for 28%, while Ca(2+), Mg(2+), Na(+) and K(+) accounted for 16% of the total ionic concentration. The ratios of Mg(2+)/Ca(2+) and Na(+)/Ca(2+) in fog water indicates that 50-75% of fog water samples correspond to the respective ratios in local soil. Significant correlation between Ca(2+), Mg(2+), Na(+) and K(+) suggests their soil origin. The order of neutralization, NH(4) (+) (1.4) > Ca(2+) (0.28) > Mg(2+) (0.12), indicates that NH(4) (+) is the major neutralizing species. Fog water and atmospheric alkalinity were also computed and were found to be 873 and 903 neqm(-3), respectively. Both of these values are higher than values reported from temperate sites and thus indicate that at the present level of pollutants, there is no risk of acid fog problem. The study also shows that the alkaline nature of fog water is due to dissolution of ammonia gas and partly due to interaction of fog water with soil derived aerosols.

Partitioning of metals between the aqueous phase and suspended insoluble material in fog droplets

This paper discusses the partitioning of metals (K, Na, Ca, Mg, Al, Cu, Fe, Pb and Zn) between the aqueous phase and the suspended insoluble material in fog samples collected in the Po Valley during two extensive fields campaigns. Metals represent on average 11% of the mass of suspended insoluble matter, while the main component is carbon (both organic carbon, OC = 35%, and black carbon, BC = 8%). The unaccounted suspended matter mass is very high, on average 46%, and is attributable to non metallic species, such as O and N and of Si. The principal metals in the insoluble suspended fraction are Fe and Al (2-5%), while the contributions of other metals (Na, Mg, Cu, Pb and Zn) are lower than 1%. Ca and K exhibited high blank values and could not be detected above blank detection limit threshold. The main components in the aqueous phase are NO3- (34%), WSOC (23%), SO4(2-) (18%) and NH4+ (19%), while trace metals and remaining cations and anions accounted for less than 1% of solute mass. The main dissolved trace metals in fog droplets are Zn, Al and Fe, while the main metallic cations are Na and Ca. Fe and Al are the only metals preferentially distributed in the suspended insoluble matter of fog droplets (partitioning ratio respectively 37% and 33%). All other metals are mostly dissolved in the aqueous phase (mean partitioning ratios of Mg, Pb, Zn, Cu and Na are 69%, 70%, 77%, 81% and 87%). These findings are in agreement with literature data on metal speciation in cloud and rain samples. The dependence of partitioning ratios on pH is investigated for the different metals, with only Al showing a clear partitioning ratio decrease with increasing pH. Conversely, the other metals show no dependence or a complex and highly variable behaviour. The partitioning ratio of iron (mean 37%) observed in the Po Valley fog samples is much higher than the water extractable iron in aerosol particles (typically 1-2 %): this fact can be explained by differences in the aerosol sources and composition among sites and by chemical processes in the aqueous phase, such as complexation and redox reactions involving organic ligands (oxalate, or other organic acids as humic-like organic matter) which may promote Fe solubility.

Monitoring of fogwater chemistry in the gulf coast urban industrial corridor: Baton Rouge (louisiana)

Seventeen fog events were sampled in Baton Rouge, Louisiana during 2002-2004 as part of characterizing wet deposition by fogwater in the heavily industrialized corridor along the Louisiana Gulf Coast in the United States. These samples were analyzed for chemical characteristics such as pH, conductivity, total organic and inorganic carbon, total metals and the principal ion concentrations. The dominant ionic species in all samples were NH4+, NO3-, Cl- and SO4(2-). The pH of the fogwater sampled had a mean value of 6.7 with two cases of acidic pH of 4.7. Rainwater and fogwater pH were similar in this region. The acidity of fogwater was a result of NO3- but partly offset by high NH4+. The measured gaseous SO2 accounted for a small percentage of the observed sulfate concentration, indicating additional gas-to-particle conversion of SO2 to sulfate in fogwater. The gaseous NOx accounted for most of the dissolved nitrate and nitrite concentration in fogwater. The high chloride concentration was attributable to the degradation of chlorinated organics in the atmosphere. The metal composition was traced directly to soil-derived aerosol precursors in the air. The major metals observed in fogwater were Na, K, Ca, Fe, Al, Mg and Zn. Of these Na, K, Ca and Mg were predominant with mean concentrations > 100 microM. Al, Fe and Zn were present in the samples, at mean concentrations < 100 microM. Small concentrations of Mn (7.8 microM), Cu (2 microM), Pb (0.07 microM) and As (0.32 microM) were also observed in the fogwaters, and these were shown to result from particulates (PM2.5) in the atmosphere. The contribution to both ions and metals from the marine sources in the Louisiana Gulf Coast was minimal. The concentrations of all principal ionic species and metals in fogwater were 1-2 orders of magnitude larger than in rainwater. Several linear alkane organic compounds were observed in the fogwater, representing the contributions from petroleum products at concentrations far exceeding their aqueous solubility. A pesticide (atrazine) was also observed in fogwater, representing the contribution from the agricultural activities nearby.

Neurokinin-1 and neurokinin-2 antagonism inhibits long-term acid fog-induced airway hyperresponsiveness

BACKGROUND

We recently reported that airway hyperresponsiveness (AHR) induced by a 6-h exposure to sulfuric acid (H(2)SO(4)) was inhibited by either the neurokinin (NK)-1 receptor antagonist, FK888, or the NK-2 receptor antagonist, SR48968, when administered immediately before the exposure. The aims of this study were to determine whether these antagonists have any therapeutic efficiency against AHR after long-term H(2)SO(4) inhalation and to elucidate the mechanisms in ovalbumin sensitized guinea pigs.

METHODS

Specific airway resistance (sRaw), AHR, and BAL fluid were analyzed after an 8-week exposure to H(2)SO(4) aerosol (82 mg/m(3), pH 1.7, 40 mOsm) or hypotonic saline solution (pH 5.9, 40 mOsm) as a control. The H(2)SO(4) group then received a 2-week treatment with FK888, SR48968, or vehicle.

RESULTS

The AHR and the eosinophil count in BAL fluid were significantly increased in the H(2)SO(4) group compared to control animals, while sRaw was significantly elevated in both groups after the 8-week exposure. Treatment with both FK888 and SR48968 significantly reduced the AHR and tended to inhibit eosinophilia in BAL fluid, but sRaw did not change. The degree of AHR improvement with SR48968 was much larger than with FK888.

CONCLUSION

Our results show that both NK-1 and NK-2 receptor antagonists inhibited long-term H(2)SO(4)-induced AHR in sensitized guinea pigs, and the effect was much greater with an NK-2 antagonist. We suggest that NK-1 or NK-2 antagonism might partially inhibit the H(2)SO(4)-induced influx of eosinophils into the lung.

High frequency of emergency room visits of asthmatic children on misty or foggy nights

STUDY OBJECTIVES

To examine whether or not the presence of mist or fog affects respiratory conditions in asthmatic children.

DESIGN

A retrospective study. PREPARATION AND METHODS: There were 754 visits by children with asthma to the emergency room at night (between 18:00 p.m. and 9:00 a.m.) during a two-year period. Meteorological data were checked at a local fire station and regional meteorological observatory. We evaluated the relation between meteorological data and the number of emergency room visits of asthmatic children.

RESULTS

The mean number of asthmatic children who visited the emergency room was higher on misty or foggy nights than on clear nights (1.2 +/- 1.2 people/night vs. 0.8 +/- 0.9 people/night, p<0.0001). Mist and fog had an increased odds ratio (OR) of emergency room visits of asthmatic children (1.74, p<0.001). In addition, increased OR was found for high atmospheric temperature (4.39, p<0.0001). Multivariate analysis showed mist and fog (p<0.0001), average atmospheric temperature (p<0.0001), and day-to-day change of temperature (p<0.05) were related to the number of asthmatic children (n=731, r=0.428, p<0.0001).

CONCLUSIONS

Our results suggest that the presence of mist and fog causes the exacerbation of asthma in children. It is not clear which is related to the high frequency of emergency room visits of asthmatic children, airborne water droplets or the meteorological condition that causes mist or fog, but the prophylaxis for exacerbation may decrease the frequency of emergency room visits.

High frequency and large deposition of acid fog on high elevation forest

We have collected and analyzed fogwater on the mountainside of Mt. Oyama (1252 m) in the Tanzawa Mountains of Japan and observed the fog event frequency from the base of the mountain with a video camera. The fog event frequency increased with elevation and was observed to be present 46% of the year at the summit. The water deposition via throughfall increased with elevation because of the increase in fogwater interception and was about twice that via rain at the summit, where the air pollutant deposition via throughfall was several times that via rainwater. The dry deposition and the deposition via fogwater were dominant factors in the total ion deposition at high elevation sites. In a fog event, nitric acid, the major acid component on the mountain, is formed during the transport of the air mass from the base of the mountain along the mountainside, where gases including nitric acid deposit and are scavenged by fogwater. Therefore, high acidity caused by nitric acid and relatively low ion strength are observed in the fogwater at high elevation sites.

Evaluation of ionic pollutants of acid fog and rain using a factor analysis and back trajectories

Fog and rain water samples were collected at the same time in the Akita Hachimantai mountain range in northern Japan from June to September in 1998 and 1999. The various ion concentrations in these samples were analyzed, and the fog droplet sizes were measured for each fog event. As the fog droplet size increased, the ion concentration decreased. The slope of log-log plots of the concentration versus the droplet size differed with the kind of ion. In order to characterize the air pollutant, moreover, these data were quantitatively analyzed by an oblique rotational factor analysis. We found that three factors were extracted as the air pollutant source: (NH4)2SO4, acids (HNO3 + H2SO4) and sea-salt. Combining the factor analysis with the 72 h back-trajectory at 850 hPa level, we found that the contribution of each factor varied with the transport pattern of air masses.

Effects of naturally-occurring acid fog on inflammatory mediators in airway and pulmonary functions in asthmatic patients

Floating fog occurs every summer in Kushiro City in Japan, and the annual average of fog water pH in the past 4 years has been under 5.0. We previously reported that epidemiologically fog was the most important positive factor contributing to increased hospital visits of asthmatic patients compared with other meteorological values and air pollutants. This study aimed to investigate the mechanism of the effects of naturally-occurring acid fog on asthmatic patients. We compared pulmonary functions and inflammatory mediators in induced sputum between the foggy (July 1995) and the non-foggy (May 1996) season, and assessed airway responsiveness to hypo-osmolar aerosol. Forty-four out of 118 asthmatic patients of Kushiro City residents participated, pulmonary function tests were completed in 36 patients, and sputum data were available in 26 patients in both seasons. Percent forced expiratory volume in 1 sec (FEV1) was significantly (P< 0.05) decreased, and % peak expiratory flow rate (PEFR) had a trend to decrease in the foggy season more than in the non-foggy, and sputum eosinophil cationic protein (ECP) and interleukin (IL)-8 were higher in the foggy season but not significantly. A moderate inverse correlation was revealed between sputum ECP and %PEFR in the foggy season (r= -0.55, P<0.005). Subjects were divided into two groups according to the best PEFR; one had >10% lower PEFR levels in the foggy season than in the non-foggy season (Group A, n = 7), the remainder did not (Group B, n = 19). In group A, sputum ECP was significantly increased (P< 0.01) in the foggy season, but there were no changes in IL-8 and prostaglandin D2. Ultrasonic nebulized distilled water provocation test revealed no differences between group A and B. These results suggested that eosinophilic inflammation rather than hypo-osmolar effect of fog might contribute to respiratory deterioration by inhalation of naturally-occurring acid fog.

Sulfate content correlates with iron concentrations in ambient air pollution particles

Current levels of air pollution particles in American cities can increase human mortality. Both the mechanism of injury and the responsible components are not known. We have postulated that injury following air pollution particle exposure is produced through a generation of oxygen-based free radicals catalyzed by metals present in the particles. As a result of its abundance in the atmosphere, sulfate appears to potentially be the most successful ligand to complex metal cations. We tested the hypothesis that (1) some portion of iron in ambient air pollution particles is present as sulfate and (2) this relationship between iron and sulfate results from the capacity of the latter to function as a ligand to mobilize the metal from the oxide. Concentrations of sulfate and iron in acid extracts of 20 filters (total suspended particles) from Utah were measured using inductively coupled plasma emission spectroscopy. In vitro oxidant generation was also measured using thiobarbituric acid-reactive products of deoxyribose. There were significant correlations between sulfate content, iron concentrations, and oxidant generation. Agitation of calcium sulfate with iron(III) oxide produced concentrations of water-soluble, catalytically active iron. We conclude that some portion of iron in the atmosphere is present as a sulfate. This relationship between sulfate and iron concentrations is likely the product of SO42- functioning as a ligand for the meal after its mobilization from an oxide by photoreduction. There were also associations between sulfate content, iron concentrations, and oxidant generation. However, sulfates had no capacity to support electron transport unless they were present with iron.

Interactions between the Encelia leaf beetle and its host plant, Encelia farinosa: The influence of acidic fog on insect growth and plant chemistry

The impact of acidic deposition on interactions between the plant Encelia farinosa and the herbivorous beetle Trirhabda geminata (Chrysomelidae) was determined under greenhouse conditions. Acidic fogs (pH 2.75) did not significantly affect the overall foliar concentrations of water or soluble protein as compared with control fogs (pH 5.6). Nonetheless, E. farinosa foliage was altered by exposure to three 3-h acidic fogs such that growth and biomass gain by T. geminata increased by more than 30% as compared to beetles feeding on control-fogged plants. Thus, previous indications that changes in soluble proteins or water content were responsible for increased biomass gain and growth of T. geminata cannot be substantiated by this study. Additionally, changes in the plant defensive chemistry were not responsible for increased herbivore growth, as farinosin, encecalin, and euparin foliar concentrations did not vary significantly between fog treatments. Significant increases in CO2 assimilation rates of E. farinosa exposed to acidic fogs were documented at 3, 7, and 21 days following treatment, suggesting that carbohydrate-based products of increased plant metabolism may have played a role (e.g. soluble carbohydrates). However, the key factors responsible for increasing herbivore performance on acidic-fogged E. farinosa remain largely unknown.

Effects of acidic aerosol, fog, mist and rain on crops and trees

The most important factors to consider for a complete determination of the toxicity to vegetation of acidic precipitation are: settling velocity, mass transfer rates, capacity to wet surfaces; number, frequency, and duration of events; and chemical composition and concentration. Meteorological factors, such as wind velocity and humidity, also must be considered because they affect the physical, temporal, and chemical properties of precipitation. Climate is important because it influences the capacity of plants to adjust, recover, or compensate for exposure to acidic precipitation. Genotype affects the efficiency of capture and capacity to tolerate acidic conditions. Aerosol and fog droplets generally are more acidic than mist and rain but they may be less phytotoxic because smaller droplets are deposited and captured less readily by leaf surfaces except when wind velocity is high. Concentrations of acids, mainly sulphuric and nitric acids, in aerosols, fog, mist, and rain in polluted regions, appear to be insufficient to produce acute injury on vegetation except perhaps in the immediate vicinity of intense sources of emissions. Chronic effects of repeated exposure to acidic precipitation, such as the impact on plant nutrition or on processes occurring at the leaf surface-atmosphere interface, and interactions with gaseous pollutants such as ozone, cannot be evaluated at present owing to the lack of information.

Effects of formaldehyde-enriched mists on Pseudotsuga menziesii (Mirbel) Franco and Lobaria pulmonaria (L.) Hoffm

The atmosphere in some areas is polluted with formaldehyde (HCHO); however, little is known about effects of HCHO on plants at concentrations resembling those in polluted areas. The effects of simulated fogwater enriched with HCHO on seedlings of Pseudotsuga menziesii (Mirbel) Franco (Douglas fir) and pendants of Lobaria pulmonaria (L.) Hoffm. were assessed. Plants were treated with HCHO-enriched fog (target concentrations of 100, 500, and 1000 microm) during five 4-night mist sessions. Growth and nitrogenase activity (acetylene reduction rate) for lichens and growth and timing of bud-break for Douglas fir were monitored. Nitrogenase activity was lowest in lichens treated at the highest HCHO concentration after all but the first mist session, and it declined significantly with increasing HCHO concentration after the final mist session (R(2) = 0.60, p = 0.02). However, differences in nitrogenase activity among treatments were generally not statistically significant (most p values from ANOVAs were >/= 0.20). Formaldehyde did not affect growth of the lichens. Budbreak of Douglas firs was slightly delayed and height growth was slightly depressed with increasing HCHO concentration, although effects were not statistically significant.

Trirhabda geminata (Coleoptera: Chrysomelidae) resistance to the direct impact of simulated acidic fog on larval growth and mortality

The direct effects of acidic fog (pH 2.75) upon the mortality and growth of Trirhabda geminata Horn (Coleoptera: Chrysomelidae), the dominant herbivore of the California coastal sage scrub, Encelia farinosa (Compositae: Asteraceae), were evaluated. Although there was a consistent pattern among and between experiments, suggesting that acidic fogs could reduce insect growth and survivorship within the first few days following application of treatments, an exposure to three consecutive, 3-h fogs over a five day period did not significantly affect mortality, biomass gain, or larval growth rate. There are two important implications from this study. First, even the highly acidic fogs found in southern California will have minimal direct effects on T. geminata performance. Second, the impacts on T. geminata biology observed in previous studies were likely mediated by host-plant responses to acidic-fog episodes.

Lack of bronchoconstrictor response to sulfuric acid aerosols and fogs

Sulfuric acid (H2SO4) is the most common acid air pollutant in the United States and is thought to have adverse respiratory effects. Sulfuric acid exists in polluted air as a dissolved solute in both small (haze) and large (fog) particles. Previous work in our laboratory has failed to demonstrate bronchoconstriction after near ambient, large-particle H2SO4 exposure in subjects with asthma. However, other investigators have found slight but significant changes in lung function following inhalation of small-particle or small-particle, low-relative-humidity (RH) H2SO4 aerosols, leading us to hypothesize that particle size and/or RH may be important variables in acid aerosol exposure. We initially studied the effects of resting inhalation of large-particle (volume median diameter, VMD, approximately equal to 6 microns) and small-particle (VMD approximately equal to 0.4 microns) aerosols with an H2SO4 concentration of 3 mg/m3 through a mouthpiece and found no effect on specific airway resistance (SRaw) or symptom scores. In a second mouthpiece study designed to compare high-RH (100%), large-particle (VMD approximately equal to 6 microns) and low-RH (less than 10%), small-particle (VMD approximately equal to 0.3 microns) aerosols with an H2SO4 concentration of 3 mg/m3, we again found no effect of either aerosol. We then examined the effects of small-particle aerosols inhaled in dry air during moderate exercise. Although breathing low-RH air during exercise provoked increases in SRaw in almost all subjects, this could not be attributed to H2SO4 since low-RH saline aerosol produced a similar result.(ABSTRACT TRUNCATED AT 250 WORDS)

The use of lichen growth abnormalities as an early warning indicator of forest dieback

Combinations of pollutants including acidic fog and ozone occur at high levels at a number of sites in eastern North America and Europe. Mountainous regions such as the Laurentians (Quebec), Appalachians (N.Y.) and the Green Mountains (Vermont) are especially vulnerable, with both conifers and hardwoods being affected. Ongoing measurements of atmospheric chemistry (e.g. The Chemistry of High Elevation Fog-CHEF project of the Canadian Atmospheric Environment Service) reveal that extreme cloudwater events of less than pH 3.0 and ozone episodes in excess of 100 ppb are common occurrences. The purpose of this study was to gather information about the response of epiphytic lichens to deteriorating air quality at selected locations for which atmospheric chemical data are readily available. A multidisciplinary approach is being used to analyse the lichens.Morphological and cellular aberrations previously documented by the authors to occur in terricolous lichens exposed to simulated acidic rain events will be evaluated for their usefulness are early warning indicators of forest decline. In addition, tissue chemistry of species such as Hypogymnia physodes will be correlated with parameters such as altitude and decline index and compared with published elemental values for lichens from similarly polluted sites in Europe and Scandinavia.