Laboratory measurements of ozone deposition to sea water and other saline solutions

Measurements of ozone deposition velocity to fresh seawater samples collected over the course of a year have been made using a static chamber technique. The magnitude of the ozone deposition velocity (ca 0.01 cm s⁻¹) was in broad agreement with the relatively few values reported in the literature. A strong correlation between ozone deposition and dissolved surfactant concentrations was found which is reflected in their similar seasonal trends. Stirring the water resulted in a significant increase in the rate of ozone uptake at the surface which suggests that wave motion may increase deposition velocity by constantly and rapidly replenishing the reactive surface organic layer.     

Transport and deposition of indoor radon decay products—I. Model development and validation

Commonly used mathematical models of indoor radon decay product behavior are based on macroscopic mass-balances, often referred to as ‘uniformly-mixed models’. The uniformly-mixed model's applicability is limited by its inability to track the movement of pollutants from their sources to other areas within the enclosure, to permit spatial- or time-dependent sources, or to take proper account of interactions with macroscopic surfaces. Although the uniformly-mixed model parameterizes the deposition process as a constant volumetric removal rate, in reality the deposition process is actually a surface phenomenon and is strongly affected by environmental conditions.This paper describes the development of RADTRAN, a two-dimensional radon progeny transport model that begins with the differential conservation equations describing the motion of air and the transport of reactive pollutants, introduces appropriate boundary conditions to represent surface deposition, and then calculates the concentration distribution of radon progeny throughout the entire region of interest. Knowing the concentration gradient near the surface, a local mass-transfer coefficient (the deposition velocity) can be determined as a function of environmental conditions. RADTRAN simulations have been based on several flow conditions: buoyancy-driven recirculating enclosure flows, free and forced-convection boundary layer flows, and one-dimensional diffusion. Free progeny diffusivity, D^f, and attachment rate, X, were varied over representative ranges. For these conditions, RADTRAN calculated free deposition velocities of u^f = 0.014–0.079 cm s⁻¹, for ²¹⁸Po. RADTRAN predictions are compared to a range of experimental measurements. It was found that the predicted range of deposition velocities is in rough agreement with findings from experiments conducted in flow conditions similar to the simplified flows used in RADTRAN.     

Analysis of atmospheric ozone measurements over a pine forest

Vertical and horizontal profiles of ozone concentration have been measured within the atmospheric boundary layer over the pine forest located in the southwest of France (Landes Forest). Evidence for an ozone depletion in lower layers is obtained from the analysis of vertical profiles recorded at the end of the night. In terms of deposition at the upper canopy level, this corresponds to a disappearance rate ranging between 0.2 and 0.5 cm s⁻¹. The horizontal profiles obtained at midday reveal that ozone vanishes at a rate of the order of 5 × 10⁻⁵ ppb m⁻¹ when air mass moving in the advection direction passes over the forested area. These results are consistent with those obtained by numeric simulation in the case of low emission rates of nitrogen oxides. On the basis of these measurements, the expression of the ozone budget within the atmospheric boundary layer is discussed and compared with the data obtained from the simulation study.     

Partitioning ozone fluxes to sparse grass and soil and the inferred resistances to dry deposition

A two-source (Penman-Monteith type) model, used in a preceding companion study as a diagnostic tool to partition objectively half-hourly measurements of evapotranspiration into bare soil and plant components and to derive in situ estimates of the bulk plant and soil resistances to evaporation, is extended to include ozone deposition. At the time this study was performed, the total leaf area index (LAI) of the site varied between 0.5 and 0.8. Live plant material accounted for 60–75% of the LAI while the remaining LAI was dead plant material. For present purposes this two-source model augments measurements of the major components of the surface energy balance and other micrometeorological measurements with measurements of the ambient ozone concentration and eddy correlation measurements of the total dry depositional flux of ozone. This study employs the bulk canopy resistances estimated previously with this model along with additional ozone measurements: (1) to partition the ozone dry deposition flux into bare soil and plant components in a region of partial canopy cover and (2) to estimate the intrinsic soil resistance to ozone destruction. The results of this study suggest: (a) that the plant component probably receives no more than 25% of the total ozone depositional flux and this percentage decreases as the soil water available to the plants decreases and (b) that the soil resistance to ozone destruction has a near-surface boundary layer component of about 0.7 s cm⁻¹ and an intrinsic component of about 1.0 s cm⁻¹.     

Transport and deposition of indoor radon decay products—II. Influence of environmental conditions

The effects of indoor radon decay product behavior on overall concentrations have generally been characterized using uniformly-mixed models, mathematical formulations based on steady-state macroscopic mass-balances, assuming uniform concentrations within the enclosure. The uniformly-mixed model parameterizes the deposition process as a constant volumetric removal rate, given different values for the free and attached progeny. The model requires prior knowledge of the deposition rates, and assumes them to be constant, independent of environmental conditions, and identical for all decay products. There has generally been little agreement regarding the actual values of the deposition rates, and the uncertainty in these required values presents an important limitation.In response to the limitations of existing mass-balance models, an indoor radon mass-transport model, RADTRAN, was developed using a microscopic mass-balance. Deposition by molecular diffusion is accounted for through boundary conditions, and deposition velocity is calculated based on the concentration distribution near the wall. Parametric sensitivity studies using RADTRAN examined the sensitivity of the deposition of radon decay products to several factors: the size of the free progeny (measured by its diffusivity, D^f), particle concentration (using the attachment rate, X), and air motion. Deposition is described in terms of the deposition velocities of the free and attached progeny, u^f and u^a. The development of RADTRAN is described in a companion paper. This paper presents the results of the parametric sensitivity studies examining the influence of environmental conditions on radon progeny deposition. Results primarily focus on the influence on the free mode of the first radon decay product, ²¹⁸Po. RADTRAN is also used to examine the variations of deposition velocity between the decay products.     

Rate constants for the gas-phase reactions of OH and NO3 radicals and O3 with sabinene and camphene at 296±2 K

The rate constants for the gas-phase reactions of sabinene and camphene, two monoterpenes emitted from vegetation, with OH and NO₃ radicals and O₃ have been determined at 296±2 K and one atmosphere total pressure of air. The OH and NO₃ radical reaction rate constants were determined using relative rate techniques. Using rate constants of k(OH + isoprene) = 1.01 × 10⁻¹⁰ cm³ molecule⁻¹ s⁻¹, k(NO₃ + trans-2-butene) = 3.87 × 10⁻¹³ cm³ molecule⁻¹ s⁻¹ and k(NO₃ + 2-methyl-2-butene) = 9.33 × 10⁻¹² cm³ molecule⁻¹ s⁻¹, the following OH and NO₃ radical reaction rate constants (in cm³ molecule⁻¹ s⁻¹ were obtained: OH radical reaction; sabinene, 1.17 × 10⁻¹⁰ and camphene, 5.33 × 10⁻¹¹; NO₃ radical reaction; sabinene, 1.01 × 10⁻¹¹, and camphene, 6.54 × 10⁻¹³. The absolute O₃ reaction rate constants determined were (in cm³ molecule⁻¹ s⁻¹ units): sabinene, 8.07 × 10⁻¹⁷, and camphene, 9.0 × 10⁻¹⁹. These rate constants are compared to literature data for other structural-related alkenes and monoterpenes.     

Formic acid and acetic acid: Emissions,atmospheric formation and dry deposition at two southern California locations

Emission rates, in situ formation rates and removal rates by dry deposition are estimated for formic acid (HCOOH, C1) and acetic acid (CH₃COOH, C2), which are the most abundant acids in southern California air and together account for much of the airborne acidity and are the leading contributors to acid dry deposition. Using data for eight unreactive tracers, direct emission rates during the fall 1987 are estimated to be 5.6 and 12.8 metric tons d⁻¹ for C1 and C2, respectively, at a coastal source-dominated site. These emissions rates increase to 9.6(C1) and 20.4(C2) metric tons d⁻¹ during the summer. In situ formation in the atmosphere via the ozone-olefin reaction is an important source for both acids. This reaction produces an estimated 25.0 and 10.1 metric tons d⁻¹ of C1 and C2, respectively, during the day and 34.5 (C1) and 4.3 (C2) metric tons d⁻¹ at night. More acetic acid than formic acid is emitted by direct sources, with C2/C1 emission rate ratios of 2.1–2.3. The reverse is true of in situ formation, with C1/C2 production rate ratios of 2.5 (day) and 8.0 (night). Dry deposition removal rates depend on season (fall > summer) and location (inland > coastal) and are 22–52 metric tons d⁻¹ for C1, and 32–83 metric tons d⁻¹ for C2. Source (emissions + in situ formation) and sink (dry deposition) terms are of the same magnitude in all six cases studied and balance each other well in three of these cases. Uncertainties in emission, in situ production and removal rates are discussed and reflect uncertaintes in olefin and unreactive tracer emission rates, yields of organic acids from the Criegee biradical (ozone-olefin reaction), and dry deposition velocity, respectively.     

Studies on the formation of H2O2 in the ozonolysis of alkenes

The formation of H₂O₂ in the reactions of ozone with alkenes, isoprene and some terpenes has been studied with tunable diode laser absorption spectroscopy. The measured yields of H₂O₂ were found to be considerably enhanced in the presence of water vapour. H₂O₂ is thought to be formed in the ozonolysis of the alkene with O₃ by direct reaction of an intermediate with water vapour. The yield of H₂O₂ relative to the reacted alkene in the ozonolysis of trans-2-butene in the presence of water vapour was also studied with long path FTIR spectroscopy. Irrespective of the analytical methods and reaction conditions applied, the H₂O₂ yields in the reaction of O₃ with the different alkenes in the presence of water vapour were found to be in the range of a few per cent or less. Under the assumption that the reactive species forming H₂O₂ in the ozonolysis is the Criegee biradical, the overall rate constants for the reactions of some biradicals with water vapour were measured relative to the rate constant of the biradical with SO₂. For the H₂COO biradical a rate constant of (5.8 ± 2.5) × 10⁻¹⁷ cm³ s⁻¹ was determined and for the (CH₃)₂COO biradical (2.9 ± 1.5) × 10⁻¹⁷ cm³ s⁻¹; in the latter case with the assumption that (CH₃)₂COO reacts with SO₂ as fast as CH₂COO.     

Laboratory studies of some halogenated ethanes and ethers: Measurements of rates of reaction with OH and of infrared absorption cross-sections

We have measured, using a conventional discharge-flow resonance-fluorescence technique, the rates of reaction between the hydroxyl radical and a series of halogenated ethanes and ethers for the temperature range 230–423 K. Our measurements gave the following Arrhenius expressions (units are cm³ molecule⁻¹ s⁻¹): CF₂HCH₃ (HFC-152), 14.2 × 10⁻¹³ exp-(1050/T); CF₂ClCH₃ (HCFC-142b), 2.6 × 10⁻¹³ exp-(1230/T); CFCl₂CH₃ (HCFC-141b), 5.8 × 10⁻¹³ exp-(1100/T); CF₃CFH₂ (HFC-134a), 5.8 × 10⁻¹³ exp-(1350/T); CF₃CF₂H (HFC-125), 2.8 × 10⁻¹³ exp-(1350/T); CF₃CCl₂H (HCFC-123), 11.8 × 10⁻¹³ exp-(900/T); CF₂HOCF₂CFClH, (enflurane), 6.1 × 10⁻¹³ exp-(1080/T); CFH₂OCH(CF₃)₂, (sevoflurane), 15.3 × 10⁻¹³ exp-(900/T). In two cases, we measured rate constants only at room temperature: CF₃CClBrH (halothane), 6 × 10⁻¹⁴ and CF₂HOCClHCF₃ (isoflurane), 2.1 × 10⁻¹⁴.We also report the following values for the integrated absorption cross-sections of the compounds in the spectral region 800–1200 cm⁻¹ in units of cm⁻² atm⁻¹: CF₂HCH₃, 1155; CF₂ClCH₃, 1422; CFCl₂CH₃, 1995; CF₃CFH₂, 2686; CF₃CF₂H, 1970, CF₃CCl₂H, 1411; CF₃CClBrH, 1400; CF₂HOCF₂CFClH, 4800; CF₂HOCClHCF₃, 3900; CFH₂OCH(CF₃)₂, 2550. We use our measurements to calculate ozone depletion potentials and greenhouse warming potentials relative to CFCl₃ for each compound.     

Polynuclear aromatic hydrocarbon degradation by heterogeneous reactions with N2O5 on atmospheric particles

The degradation of particulate polynuclear aromatic hydrocarbons (PAH) on atmospheric soot particles in the presence of gas phase dinitrogen pentoxide (N₂O₅) was explored. Dilute diesel and wood soot particles containing PAH were reacted with∼10ppm of N₂O₅ in a 200 ℓ continuous stirred tank reactor (CSTR). To provide a stable source of particles for reaction in the CSTR, diesel or wood soot particles were injected at night into a 25 m³ Teflon outdoor chamber. The large chamber served as a reservoir for the feed aerosol, and the aerosol could then be introduced at a constant flow rate into the CSTR. PAH-N₂O₅ heterogeneous rate constants for wood soot at 15°C ranged from2 × 10⁻¹⁸to5 × 10⁻¹⁸ cm³ molecules⁻¹ s⁻¹. For diesel soot the rate constants at 16°C were higher and ranged from5 × 10⁻¹⁸to30 × 10⁻¹⁸ cm³ molecules⁻¹ s⁻¹. Comparisons with other studies suggest that sunlight is the most important factor which influences PAH decay. This is followed by ozone, NO₂, N₂O₅ and nitric acid. The rate constants of nitro-PAH formation from a parent PAH and N₂O₅ were of the order of1 × 10⁻¹⁹−1 × 10⁻¹⁸ molecules⁻¹s⁻¹. The uncertainty associated with all of these rate constants is± a factor of 3. Given, however, the small magnitude of the rate constants and the low levels of N₂O₅ present in the atmosphere, we concluded that PAH heterogeneous reactions with gas phase N₂O₅ degrade particle-bound PAH or to form nitro-PAH from PAH arenot very important. (Direct application of the specific rate constants derived in this study to ambient atmospheres should not be undertaken unless the ambient particle size distributions and chemical composition of the particles are similar to the ones reported in this study.)     

Transported acid aerosols measured in southern Ontario

During the period 29 June 1986–9 August 1986, a field health study assessing the acute health effects of air pollutants on children was conducted at a summer girls' camp on the northern shore of Lake Erie in SW Ontario. Continuous air pollution measurements of SO₂, O₃, NO_x, particulate sulfates, light scattering, and meteorological measurements including temperature, dew point, and wind speed and direction were made. Twelve-hour integrated samples of size fractioned particles were also obtained using dichotomous samplers and Harvard impactors equipped with an ammonia denuder for subsequent hydrogen ion determination. Particulate samples were analyzed for trace elements by X-ray fluorescence and Neutron Activation, and for organic and elemental carbon by a thermal/optical technique. The measured aerosol was periodically very acidic with observed 12-h averaged H⁺ concentrations in the range < 10–560 nmoles m⁻³. The aerosol H⁺ appeared to represent the net strong acidity after H₂SO₄ reaction with NH₃(g). Average daytime concentrations were higher than night-time for aerosol H⁺, sulfate, fine mass and ozone. Prolonged episodes of atmospheric acidity, sulfate, and ozone were associated with air masses arriving at the measurement site from the west and from the southwest over Lake Erie. Sulfate concentrations measured at the lakeshore camp were more than twice those measured at inland sites during extreme pollution episodes. The concentration gradient observed with onshore flow was potentially due to enhanced deposition near the lakeshore caused by discontinuities in the meteorological fields in this region.     

Measurements of ammonia flux to a spruce stand in Denmark

This work demonstrates the existence of a linear relation between the deposition velocity of ammonia and the friction velocity measured above a spruce stand in the western part of Denmark. In order to estimate the ammonia deposition velocity and flux to a Norway spruce forest, concentration gradients of ammonia and several meteorological parameters were measured in a meteorology tower during two periods, 1 week in spring and 1 week in late summer 1991. The estimated deposition velocities lie in the range −0.125 to 0.201 m s⁻¹, with a mean of 0.026 m s⁻¹. The deposition velocity and the flux were generally largest in the afternoon. On the basis of 24-h measurements of ammonia and routine meteorological measurements the relation between deposition velocity and friction velocity is extrapolated to an estimate of the average flux for the growing season May to September 1991. The estimate gave an average flux of 87 μg NH₃N m⁻² h⁻¹ (=0.02 μg NH₃N m⁻² s⁻¹). The average deposition velocity for the period was 0.045 m s⁻¹.     

Measurement and modeling of airbone concentrations and indoor surface accumulation rates of ionic substances at Neenah,Wisconsin

The objective of this continuing investigation of indoor/outdoor/surface relationships has been to develop an accurate method for predicting and subsequently managing the accumulation rates and ultimately the effects of corrosive substance on electronic equipment surface in field and manufacturing environments. We previously reported indoor/outdoor ratios and deposition velocities for Cl⁻, SO₄²⁻, Na⁺, NH₄⁺, Mg²⁺ and Ca²⁺ associated with fine and coarse particles at telephone company switching equipment locations in Wichita (Kansas), Lubbock (Texas) and Newark (New Jersey). Using the results from these studies, a methodology was developed for predicting the average indoor surface accumulation rates of ionic substances from their outdoor concentrations.In this paper we report new results for a site at Neenah, Wisconsin. At this site detailed data on the operational status of the air handling euipment were also obtained through a permanent monitoring system. These data and the data on ionic species have been used in mass balance model that calculates indoor concentrations from outdoor concentrations. Coupling this mass balance model with the measured deposition velocities substantially improves the earlier methodology for predicting surface accumulation rates from outdoor concentrations and enables decision makers to evaluate the effects of various manipulations in critical air handling system operating variables. Informed decisions can now be made when striking a balance between energy and indoor use and indoor air quality or equipment reliability.     

Hydrophobic organic chemicals in urban fog

The concentrations and aqueous/particle distributions of three classes of hydrophobic organic chemicals, n-alkanes, polycyclic aromatic hydrocarbons (PAHs), and polychlorinated biphenyls (PCBs) were measured during the autumn of 1986's fog events in the urban area of Zürich, Switzerland. Concentrations of the chemicals in fog were in the range of 10–110 ng ml⁻¹ for n-alkanes (C₁₉–C₃₅), 6–60 ng ml⁻¹ for PAHs (21 compounds) and 7–22 ng ml⁻¹ for PCBs (31 congeners). In many samples, the concentration of individual n-alkanes and PAHs exceeded their water solubility, probably due to their association with dissolved and/or colloidal organic matter. All of the PAHs, except for phenanthrene, were measured as part of the particulate phase. Both the n-alkanes and PCBs showed a trend of increasing particle association with increasing hydrophobicity, but the trends were distinctly different. The presence of PCBs, PAHs, and n-alkanes at these concentrations suggest that fog is an excellent scavenger of hydrophobic organic chemicals. For a forested area near Zürich, Switzerland, it was estimated that the deposition of n-alkanes and PAHs by fog may be about equal to deposition via rain, but that fog may be 100 times more important than rain for the deposition of PCBs.     

Monitoring the dry deposition of SO2 in the Netherlands: Results for grassland and heather vegetation

An automated system based on the micrometeorological gradient technique has been developed to measure the dry deposition of SO₂ on a routine basis. Measurements were made at two locations in the Netherlands. From these results dry deposition fluxes, dry deposition velocities and surface resistances for a heathland and for an agricultural grassland site were estimated using a selected set of data and a calculation procedure based on micrometeorological considerations. An extensive analysis was made to determine uncertainties in the resulting deposition parameters. From this analysis it has been concluded that the uncertainty in these parameters is almost completely determined by the random errors in measured concentrations. The meteorological surface exchange parameters can be estimated sufficiently accurately (<20% uncertainty). At the grassland site, average surface resistances to deposition of 6(±8) and 13(±12) s m⁻¹ were calculated for wet and dry conditions, respectively. At the heathland site, a similar distinct difference between R_c values for wet and dry conditions was found. These values are 20(±21) and 70(±90) s m⁻¹, respectively. The yearly average dry deposition flux for SO₂ at the grassland site amounts to 585(±330) mol ha⁻¹ yr⁻¹, while at the heathland site the yearly average flux was 300(±270) mol ha⁻¹ yr⁻¹. The yearly average dry deposition velocity at 4 m height was 1.2(±0.3) cm s⁻¹ at the grassland site and 0.8(±0.4) cm s⁻¹ at the heathland site.     

The stem-II regional scale acid deposition and photochemical oxidant model—IV. The impact of emission reductions on mesoscale acid deposition in the lower ohio river valley

Assessment of the effect of reduction in emissions of primary sources on eventual levels of pollutants, pH of precipitation and total wet deposition is crucial in designing acid-rain control strategies. The STEM-II/ASM model is used to investigate the effect of reduction in emissions on the ultimate deposition patterns and amounts of major acidic pollutants in a mesoscale region. This work also investigates the effect of background levels of primary pollutant species on the eventual levels and deposition amounts of SO₄⁼ and NO₃⁻. A series of mesoscale simulations were conducted in which emissions of primary sources of NO_x and SO₂ were reduced and/or background concentrations of certain key species were changed. The results indicate that the dominant effect on the eventual deposition amounts of SO₄⁼ and NO₃⁻ is due to background concentrations of key precursor species such as SO_x and NO_x. With relatively high background concentrations, reducing SO₂ emissions by 50% and NO_x emissions by 40% resulted in reductions of 2–3% for SO₄⁼ wet deposition aand about 15% for NO₃⁻ wet deposition. However, reducing the background concentrations of SO₂ and SO₄⁼ by 50% and NO, NO₂ and HNO₃ by 40% resulted in substantial reductions in wet deposition; SO₄⁼ deposition was reduced by 40–50% and NO₃⁻ deposition was reduced by approximately 35%.     

Environmental chamber study of the photochemical reaction of ethyl methyl sulfide and Nox

A series of experiments were conducted in a self-made smog chamber at 300 ± 1 K and 1.01×105 Pa to simulate the photochemical reaction of ethyl methyl sulfide (EMS) and NOx. The results show that the higher the initial concentration of EMS, the more ozone is generated in the simulative reactions. It is found that the light intensity plays a very important role in the evaluation of ozone formation potential for EMS. The parameters of d(O3-NO) and IR (incremental reactivity) were used to quantify the potential of EMS on ozone formation. The obtained maximum IR values in this paper for the five simulative reactions were 1.55×10-2, 0.99×10-2, 1.36×10-2, 2.47×10-2, and 1.65×10-2, respectively. Comparison between the results we obtained here and the results we obtained before for di-tert-butyl peroxide and acetylene was made and it showed that the potential reactivity of EMS on ozone formation is at a relatively low level.     

Characteristics of airborne particles inside southern California museums

The concentrations and chemical composition of suspended particulate matter were measured in both the fine and total size modes inside and outside five southern California museums over summer and winter periods. The seasonally averaged indoor/outdoor ratios for particulate matter mass concentrations ranged from 0.16 to 0.96 for fine particles and from 0.06 to 0.53 for coarse particles, with the lower values observed for buildings with sophisticated ventilation systems which include filters for particulate matter removal. Museums with deliberate particle filtration systems showed indoor fine particle concentrations generally averaging less than 10 μg m⁻³. One museum with no environmental control system showed indoor fine particle concentrations averaging nearly 60 μg m⁻³ in winter and coarse particle concentrations in the 30–40 μg m⁻³ range. Analyses of indoor vs outdoor concentrations of major chemical species indicated that indoor sources of organic matter may exist at all sites, but that none of the other measured species appear to have major indoor sources at the museums studied. Significant fractions of the dark-colored fine elemental (black) carbon and soil dust particles present in outdoor air are able to penetrate to the indoor atmosphere of the museums studied, and may constitute a soiling hazard to works of art displayed in museums.     

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

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

The investigation of air quality and acid rain over the Gulf of Mexico

A research cruise was conducted in the summer of 1986 by a group of scientist from the U.S.A. and Mexico to investigate air chemistry over the Gulf of Mexico. Chemical, physical, meteorological and oceanographic measurements were carried out to survey temporal and spatial variations of diverse parameters throughout the Gulf. Emphases were placed on air-sea-land exchange of gases and aerosols, natural air quality, transport of anthropogenic air pollution, and acid rain deposition to the Gulf. Although the prevailing winds were easterly from the sea during the cruise, the air was highly polluted with continental aerosols, probably caused by local shifting winds and the oscillation between sea breeze and land breeze. Aerosol number concentrations were measured from 10⁵ cm⁻³ at ports to 10³ cm⁻³ in the open Gulf. The average aerosol mass concentration was ∼25μg M⁻³, consisting of 60% insoluble crustal particles that contained Si, Al, Fe; 30% seasalt particles that contained Na⁺ and Cl⁻; and 10% anthropogenic sulfate and nitrate particles. Samples of rain water collected near the coast were acidic (pH ∼4). The concentrations of dimethyl sulfide correlated with bio-particle concentrations in surface seawater and could be a significant precursor of atmospheric SO₄²⁻ particles. The life cycles of the aerosols in the Gulf, including sources, transport, transformation, and wet and dry deposition are discussed.