Nitrate and natural organic matter in aqueous solutions irradiated by simulated sunlight

By means of simulated sunlight, the influence of natural organic matter (NOM) on the photochemical degradation of halogenated pesticides in the absence and presence of nitrate as a precursor of the highly reactive OH radicals in aqueous solutions and freshwater was investigated. Solutions of dichlorprop or terbutylazine (a) in phosphate-buffered demineralized water containing nitrate and/or NOM and (b) in natural freshwaters were irradiated by a 1000-W Xe short-arc lamp. The collimated beam was filtered using a combination of optical filters (WG 320 and WG 295) to simulate the solar spectrum under summer midday conditions. In the absence of nitrate and NOM, the pesticides were degraded photolytically by simulated sunlight. The degradation rates depended on the absorption spectrum in the UVB range and the quantum yield of the degradation. The photochemical degradation of the pesticides was faster in the presence of nitrate due to the sunlight-induced formation of OH radicals. In the absence of nitrate, low concentrations of NOM of a brownwater lake accelerated the degradation due to the formation of reactive species by NOM. At higher concentrations of NOM, the inner filter effect of NOM lowered the degradation rates. In the presence of 50 mg l−1 nitrate, NOM decreased the degradation rate significantly. In case the natural water samples were used as a matrix for the experiments (nitrate concentrations between 2 mg l−1 and 15 mg l−1, DOC concentrations below 2.3 mg l−1), NOM acted mainly as a radiation filter and as a scavenger of OH radicals. As a consequence, in most freshwater systems, the accelerating effect of NOM by the formation of reactive species is of minor importance compared to the inner filter effect and to radical scavenging.     

Heterogeneous light-induced ozone processing on the organic coatings in the atmosphere

Many of the more recent studies concerning heterogeneous reactions of atmospheric interest, carry, in some cases, much more details but still follow the basic philosophy of the first pioneering studies. Therefore, in this study the accent is put on the additional complexities that arise when the aerosols of interest have more complex compositions. Hence, it is attempted to identify the products following the simultaneous ozone processing and light irradiation on particles coated with 4-phenoxyphenol in the presence of 4-carboxybenzophenone as a photosensitizer. In order to reveal a more complete picture on the fate of these aromatic compounds under controlled experimental conditions, different analytical tools such as gas chromatography coupled to mass spectrometry (GC–MS) and proton transfer reaction-mass spectrometry (PTR-MS) have been applied.Several surface bound products were identified via GC–MS and some of them (phenol, hydroquinone, catechol, 4-hydroxybenzoic acid, benzoic acid, fumaric acid, terephthalic acid, maleic acid, 1,2,4-trihydroxybenzene and 4,4′-oxydiphenol) confirmed with standards. The main volatile secondary products as identified by PTR-MS in this study were formic acid, phenol and p-benzoquinone.A reaction mechanism was proposed and density functional theory calculations were performed in order to elucidate the initial steps of the ozonolysis reaction on 4-phenoxyphenol in the presence of 4-carboxybenzophenone.     

Impact of biogenic emission uncertainties on the simulated response of ozone and fine particulate matter to anthropogenic emission reductions

The role of emissions of volatile organic compounds and nitric oxide from biogenic sources is becoming increasingly important in regulatory air quality modeling as levels of anthropogenic emissions continue to decrease and stricter health-based air quality standards are being adopted. However, considerable uncertainties still exist in the current estimation methodologies for biogenic emissions. The impact of these uncertainties on ozone and fine particulate matter (PM2.5) levels for the eastern United States was studied, focusing on biogenic emissions estimates from two commonly used biogenic emission models, the Model of Emissions of Gases and Aerosols from Nature (MEGAN) and the Biogenic Emissions Inventory System (BEIS). Photochemical grid modeling simulations were performed for two scenarios: one reflecting present day conditions and the other reflecting a hypothetical future year with reductions in emissions of anthropogenic oxides of nitrogen (NOx). For ozone, the use of MEGAN emissions resulted in a higher ozone response to hypothetical anthropogenic NOx emission reductions compared with BEIS. Applying the current U.S. Environmental Protection Agency guidance on regulatory air quality modeling in conjunction with typical maximum ozone concentrations, the differences in estimated future year ozone design values (DVF) stemming from differences in biogenic emissions estimates were on the order of 4 parts per billion (ppb), corresponding to approximately 5% of the daily maximum 8-hr ozone National Ambient Air Quality Standard (NAAQS) of 75 ppb. For PM2.5, the differences were 0.1-0.25 microg/m3 in the summer total organic mass component of DVFs, corresponding to approximately 1-2% of the value of the annual PM2.5 NAAQS of 15 microg/m3. Spatial variations in the ozone and PM2.5 differences also reveal that the impacts of different biogenic emission estimates on ozone and PM2.5 levels are dependent on ambient levels of anthropogenic emissions.     

Characterization of organic coatings on hygroscopic salt particles and their atmospheric impacts

The photooxidation of α-pinene in the presence of NO₂, with and without added NaNO₃ seed particles, has been studied in a large-diameter flow tube. Particles formed by homogeneous nucleation and by condensation on the pre-existing seeds were sampled at various stages of the reaction, dried using four diffusion dryers, size selected at different mobility diameters (d_m) using a differential mobility analyzer (DMA), and characterized with a single particle mass spectrometer (SPLAT II). It was found that homogeneously nucleated particles are spherical, have a density (ρ) of 1.25 ± 0.02 g cm^?3 (±2σ) and contain a significant amount of organic nitrates. The mass spectra of the low volatility products condensed on the NaNO₃ seed particles were found to be virtually the same as in the case of homogeneous nucleation. The data show that the presence of even a submonolayer of organics on the NaNO₃ particles causes water retention that leads to a decrease in particle density and that the amount of water retained increases with organic coating thickness. Thicker coatings appear to inhibit water evaporation from the particle seeds altogether. This suggests that in the atmosphere, where low volatility organics are plentiful, some hygroscopic salts will retain water and have different densities and refractive indices than expected in the absence of the organic coating. This water retention combined with the organic shell on the particles can potentially impact light scattering by these particles and activity as cloud condensation nuclei (CCN), as well as heterogeneous chemistry and photochemistry on the particles.     

Light-induced heterogeneous ozone processing on organic coated particles: Kinetics and condensed-phase products

For the first time we investigated the effect of solar irradiation upon the heterogeneous ozonation of adsorbed 3,4,5-trimethoxybenzaldehyde on solid surface. Light-induced heterogeneous reactions between gas-phase ozone and 3,4,5-trimethoxybenzaldehyde adsorbed on silica particles were performed and the consecutive reaction products were identified. At an ozone mixing ratio of 250 ppb, the loss of 3,4,5-trimethoxybenzaldehyde ranged from 1.0 · 10^?6 s^?1 in the dark to 2.9 · 10^?5 s^?1 under light irradiation. Such large enhancement of 29 times clearly shows the importance of light (λ > 300 nm) during the heterogeneous ozonolysis on organic coated particles.The reaction products identified in this study (3,4,5-trimethoxybenzoic acid, syringic acid, methyl 3,4,5-trimethoxybenzoate) absorb light in the spectral window (λ > 300 nm) which implies that light-induced heterogeneous ozone processing can have an influence on the aerosol surfaces by changing their physico-chemical properties.The main identified product of the heterogeneous reactions between gas-phase ozone and 3,4,5-trimethoxybenzaldehyde under dark conditions and in presence of light was 3,4,5-trimethoxybenzoic acid. For this reason we estimated the carbon yield of 3,4,5-trimethoxybenzoic acid. Carbon yields of 3,4,5-trimethoxybenzoic acid decreased with increasing ozone mixing ratio; from 40% at 250 ppb to 15% at ≥2.5 ppm under dark conditions. At ozone mixing ratio (250 ppb–1 ppm), carbon yields of 3,4,5-trimethoxybenzaldehyde are relatively higher in the experiment under dark condition than under simulated solar light.     

Mycorrhizal populations and fine root development on Norway spruce exposed to controlled doses of gaseous pollutants and simulated acidic rain treatments

Effects after long-term fumigation and simulated acidic rain (pH 4.0) treatment in open-top chambers (OTC) during 5 vegetation periods on ectomycorrhizal (EM) frequency, fine root structure and distribution of short roots were recorded for Norway spruce. Simultaneous application of ozone and SO(2) resulted in a significant decrease (P< or =0.01) in the proportion of EM root tips and an increase in the numbers of necrotic short roots. The observed differences were partly due to more than additive effects of ozone and SO(2). On the basis of EM and non-mycorrhizal (NM) short roots in the irrigated controls (OTC-V, pH 5.6, Ah-horizon: EM + NM/cm=0.05) the acid treatments resulted in drastic effects (P< or =0.05) on the branching density and the proportion of EM root tips and NM short roots. Relative numbers of short roots infected by indigenous EM fungi with trees in the fumigation treatments at pH 4.0 were similar: 1.5-1.9 EM tips/cm and differed noticeably from the control: 5.2 EM tips/cm. Again, increasing numbers of necrotic and NM short roots were noted. Parallel measurements by the ingrowth-core technique confirm the argument, that EM formation seems to be a reliable indicator of pollution-induced stress.     

The inportance of organic and elemental carbon in the fine atmospheric aerosol particles

During a field campaign the chemical character of fine (d<2.5 μm) aerosol particles was studied at K-puszta, Hungary within the framework of a project of the European Union. The organic and elemental carbon fraction, as well as the concentration of major inorganic constituents with respect to the total fine aerosol mass are presented in this paper. It was found that organic compounds constituted a significant fraction of the total fine aerosol mass, their contribution is comparable to or larger than that of the major water soluble ions. The diurnal variation of aerosol composition was also studied. It can be concluded that the relative abundance of the major constituents is practically the same during the day and at night. The samples were also classified and studied according to the air mass history. It is stated that the aerosol can be separated into two populations with different regression lines between organic and elemental carbon.     

Yield loss assessments for cultivars of broccoli, lettuce, and onion exposed to ozone

The effects of the photochemical oxidant air pollutant ozone (O(3)) on growth and yield of three garden crops, broccoli (Brassica oleracea L.), lettuce (Lactuca sativa L.), and onion (Allium cepa L.) were studied in an open-top chamber experiment conducted in the field in southern California. Four cultivars each of leaf lettuce, broccoli, and globe onion were exposed to charcoal-filtered air (CF), non-filtered (NF) air, or NF plus 1.5 times ambient O(3) concentration from 4 weeks after germination in January or February until harvest. Exposures lasted 31 days for lettuce, 55 to 78 days for broccoli, and 105 days for onion. Results showed that despite severe O(3) injury to outer leaves, lettuce yields were not affected by O(3). Broccoli also was resistant to O(3) and no growth reduction was observed at ambient O(3) concentrations. Onions were more susceptible to O(3), but only one cv. 'Rio Bravo' had significant yield losses (ca. 5%) at ambient O(3) levels. These results suggest that, in general, concentrations of O(3) in the winter and spring may be below the threshold for adverse effects on yields of broccoli, lettuce and onion.     

Sources of personal exposure to fine particles in Toronto, Ontario, Canada

Individuals are exposed to particulate matter from both indoor and outdoor sources. The aim of this study was to compare the relative contributions of three sources of personal exposure to fine particles (PM2.5) by using chemical tracers. The study design incorporated repeated 24-hr personal exposure measurements of air pollution from 28 cardiac-compromised residents of Toronto, Ontario, Canada. Each study participant wore the Rupprecht & Patashnick ChemPass Personal Sampling System 1 day a week for a maximum of 10 weeks. During their individual exposure measurement days the subjects reported to have spent an average of 89% of their time indoors. Particle phase elemental carbon, sulfate, and calcium personal exposure data were used in a mixed-effects model as tracers for outdoor PM2.5 from traffic-related combustion, regional, and local crustal materials, respectively. These three sources were found to contribute 13% +/- 10%, 17% +/- 16%, and 7% +/- 6% of PM2.5 exposures. The remaining fraction of the personal PM2.5 is hypothesized to be predominantly related to indoor sources. For comparison, central site outdoor PM2.5 measurements for the same dates as personal measurements were used to construct a receptor model using the same three tracers. In this case, traffic-related combustion, regional, and local crustal materials were found to contribute 19% +/- 17%, 52% +/- 22%, and 10% +/- 7%, respectively. Our results indicate that the three outdoor PM2.5 sources considered are statistically significant contributors to personal exposure to PM2.5. Our results also suggest that among the Toronto subjects, who spent a considerable amount of time indoors, exposure to outdoor PM2.5 includes a greater relative contribution from combustion sources compared with outdoor PM2.5 measurements where regional sources are the dominant contributor.     

Decomposition of benzo (a) pyrene deposited on glass fiber filters and exposed to sunlight

Measurements of Benzo (a) Pyrene deposited on glass fiber filters exposed to solar radiation indicate a time dependent exponential decrease. Possible impl$\text{i}$ cations of this phenomenon in the measurements of B(a)P in particulate samples are discussed.     

Responses to ozone pollution of alfalfa exposed to increasing salinity levels

Stomatal closure and biosynthesis of antioxidant molecules are two fundamental components of the physiological machinery that lead to stress adaptation during plant's exposure to salinity. Since high stomatal resistance may also contribute in counteracting O₃ damages, we hypothesized that soil salinization may increase O₃ tolerance of crops. An experiment was performed with alfalfa grown in filtered (AOT40 = 0 in both years) and non-filtered (AOT40 = 9.7 in 2005 and 6.9 ppm h in 2006) open-top chambers. Alfalfa yield was reduced by O₃ (−33%) only in plants irrigated with salt-free water, while the increasing levels of soil salinity until 1.06 dS m⁻¹ reduced both stomatal conductance and plant O₃ uptake, thus linearly reducing O₃ effects on yield. Therefore a reliable flux-based model for assessing the effects of O₃ on crop yield should take into account soil salinity.     

Yields of field-grown soybeans exposed to simulated acidic deposition

Rainfall acidity response functions for crop yield and growth are necessary to predict the overall impacts on crop yields of ambient and/or anticipated levels of acidic rain. The experiment described herein was performed at Brookhaven National Laboratory during 1984 and 1985 to determine the effects of simulated rainfalls of pH 5.6, 4.4, 4.1 and 3.3 on seed yields of four cultivars of field-grown soybeans (Glycine max Merrill). Soybeans were chosen because previous results suggested that certain varieties of this crop are sensitive to rainfall acidity and because they are an economically important crop in the USA. Sixteen plots per treatment were used. Plants were grown using standard agronomic practices under automatically movable exclusion shelters which minimize changes in the plant's microclimate. Analysis of variance of seed yields of the four cultivars showed significant treatments for all four cultivars. For all cultivars, seed yields were lower when exposed to simulated rainfalls of pH 4.4, 4.1 and 3.3 compared with rainfalls of pH 5.6. Compared with pH 5.6 rainfall (controls), yields of Amsoy exposed to pH 4.4, 4.1 and 3.3 were lower by 13, 11 and 12%, respectively. The percentage yield reductions for Asgrow, Corsoy and Hobbit were not as great as those of Amsoy. Averaged over all cultivars tested, there was a 9% seed reduction for plants exposed to simulated rain at pH 4.1 (comparable to ambient) compared with pH 5.6.     

Response of sugar maple to multiple year exposures to ozone and simulated acidic precipitation

Potted sugar maple seedlings were exposed to ozone and acidic precipitation in open-top chambers for three consecutive growing seasons. Periodic measurements of photosynthesis, dark respiration, through-fall and soil solution chemistry, and annual measurements of the weight of plant parts were made. Experimental treatments caused few and minor effects on above- or below-ground growth of the seedlings, even after three growing seasons. There were trends for reduced photosynthesis in trees exposed to elevated concentrations of ozone and increased photosynthesis in those exposed to the lowest pH simulated rain treatment. The chemistries of soil-solutions and through-fall were not altered significantly by treatment. Although major effects were not observed, sugar maple may respond to exposures that take place over a significant part of its life cycle.     

Chemical coupling between ammonia, acid gases, and fine particles

The concentrations of inorganic aerosol components in the fine particulate matter (PM(fine)< or =2.5 microm) consisted of primarily ammonium, sodium, sulfate, nitrate, and chloride are related to the transfer time scale between gas to particle phase, which is a function of the ambient temperature, relative humidity, and their gas phase constituent concentrations in the atmosphere. This study involved understanding the magnitude of major ammonia sources; and an up-wind and down-wind (receptor) ammonia, acid gases, and fine particulate measurements; with a view to accretion gas-to-particle conversion (GTPS) process in an agricultural/rural environment. The observational based analysis of ammonia, acid gases, and fine particles by annular denuder system (ADS) coupled with a Gaussian dispersion model provided the mean pseudo-first-order k(S-1) between NH(3) and H(2)SO(4) aerosol approximately 5.00 (+/-3.77)x10(-3) s(-1). The rate constant was found to increase as ambient temperature, wind speed, and solar radiation increases, and decreases with increasing relative humidity. The observed [NH(3)][HNO(3)] products exceeded values predicted by theoretical equilibrium constants, due to a local excess of ammonia concentration.     

Spectroscopic study of the interaction of heavy metals with organic acids

The ongoing progress in spectroscopic methods of analysis has resulted in a growing interest in the nature of pollutants and hence the possibility of controlling their levels in the environment. This paper describes a study of the fate of some pollutants in both soil and water at two selected areas in the north of Cairo, Egypt. Samples were collected from Shoubra Elkhima and Kafr ElSheikh during October 2003 and October 2004, respectively. Atomic absorption spectrometry was used to evaluate the level of cadmium, chromium, copper, iron, lead and zinc in the collected samples. In addition, Fourier transform infrared spectroscopy was used to investigate the molecular structure of soil samples. Results indicate that there is a possible interaction between heavy metals and humic acid, which is manifested by a noticeable shift in the absorption of the carboxyl group towards lower frequencies as a result of metal interaction. Furthermore, it is concluded that the carboxylate group of humic acid leads the transport of metals from soil to groundwater.     

Growth, ectomycorrhizae and nonstructural carbohydrates of loblolly pine seedlings exposed to ozone and soil water deficit

Loblolly pine (Pinus taeda) seedlings from three full-sib families were exposed to 0, 50, 100 or 150 ppb ozone (O(3)) (5 h/d, 5 d/week for 6 or 12 weeks). Soil water potential was maintained near pot capacity (-0.03 MPa) or soil was allowed to dry to approximately -1.0 MPa and resaturated. Chlorotic mottling and flecking of needles due to O(3) injury were observed for seedlings from all pine families. Soil water deficit lessened the intensity of O(3) symptoms, possibly due to stomatal closure. Exposure to O(3) and soil water deficit each resulted in less seedling volume growth and dry weight, and changed the nonstructural carbohydrate content of seedlings compared with controls. Increasing O(3) concentrations resulted in a linear reduction in foliar starch content but did and affect hexose or sucrose content. Soil water deficit resulted in less starch and soluble sugar contents in above- and below-ground plant parts compared with controls. Soil water deficit did not affect numbers or percentages of roots that formed ectomycorrhizal tips. A linear dose-response relationship between O(3) and ectomycorrhizae was observed. The number of ectomycorrhizal tips/cm long root and the percentage of feeder roots that formed ectomycorrhizae were lower as O(3) concentration increased. Overall, each stress alone caused less seedling growth and carbohydrate content compared with controls, but only O(3) was responsible for suppression of ectomycorrhizae.     

Characterization of saccharides and other organic compounds in fine particles and the use of saccharides to track primary biologically derived carbon sources

A total of 134 aerosol samples (d_p < 2.5 μm) were collected at one rural site and one urban site in Texas from November 2005 to July 2006 to investigate the different sources that contribute to the ambient levels of different compounds. In particular, saccharide compounds were studied as potential tracers to track aerosols of biologically derived origin. The ambient concentration, seasonal variation, and urban/rural comparison of major saccharides and other organic compounds including normal alkanes, hopanes, and carboxylic acids were determined and analyzed relative to characterizing sources of PM2.5. Saccharides, together with other known molecular markers, were analyzed by a positive matrix factorization model and eight source factors were isolated that provide meaningful interpretation of aerosol sources. Three isolated factors were characterized by the dominance of different saccharide compounds and were attributed to wood smoke, sucrose rich bio-aerosols, and fungal spore derived bio-aerosols. It was estimated that wood smoke and primary biologically derived carbon sources contributed 22% and 14% to the measured ambient PM2.5 mass at San Augustine and 16% and 5% to the measured ambient PM2.5 mass at Dallas. The relative PM contribution from other resolved sources were also calculated.     

Diminished greenness of tomato leaves exposed to ozone and post-exposure recovery of greenness

The response to ozone (O(3)) of greenness, in terms of estimated total chlorophyll concentration (Chl), of leaves at three plant canopy levels was studied in tomato (Lycopersicon esculentum Mill.) over a 10-day period following O(3) exposure. Plants of the cultivars 'New Yorker' and 'Tiny Tim' were grown at 25/15 degrees or 30/15 degrees day/night temperatures in growth chambers and exposed to 0.00, 0.08, 0.16 or 0.24 microl litre(-1) O(3) for 7 h day(-1) for four consecutive days in controlled environment exposure chambers. Measurement of Chl in the top, middle and bottom canopy leaves with a calibrated SPAD-501 leaf greenness meter indicated that the growth temperatures tested did not significantly influence the response of Chl to O(3). Ozone-induced loss of Chl was widespread in the entire foliage canopy, including foliage which did not demonstrate visible injury. In both cultvars the Chl in leaves at all three canopy levels declined as a function of increasing O(3) concentration when measured 2, 4, 6, 8 and 10 days after the exposure period. However, the slopes for leaves in the top and middle canopies decreased with increasing time after exposure. An analysis of this apparent Chl recovery indicated that leaves in the top and middle canopies exposed to 0.16 and 0.24 microl litre(-1) increased in greenness at a rapid rate after the marked initial decline associated with O(3) treatment. The apparent recovery of the top canopy may have reflected the growth of new leaves and their inclusion in the measurements, but this was not the case for the middle canopy for which the same leaves were measured throughout the post-exposure period. Bottom canopy leaves did not demonstrate significant recovery of Chl.     

Heterogeneous reactions of ozone with pyrene, 1-hydroxypyrene and 1-nitropyrene adsorbed on particles

This work deals with the kinetic study of the reactions of ozone with pyrene, 1-hydroxypyrene and 1-nitropyrene, adsorbed on model particles. Experiments were performed at room temperature and atmospheric pressure, using a quasi-static flow reactor in the absence of light. Compounds were extracted from particles using pressurized fluid extraction (PFE) and concentration measurements were performed using gas chromatography/mass spectrometry (GC/MS). The pseudo-first order rate constants were obtained from the fit of the experimental decay of particulate polycyclic compound concentrations versus reaction time. Experiments were performed at three different O₃ concentrations from which second order rate constants were calculated. The following rate constant values were obtained at 293 K: k(O₃ + Pyrene) = (3.2 ± 0.7) × 10^?16 cm³ molecule^?1 s^?1; k(O₃ + 1OHP) = (7.7 ± 1.4) ×10 ^?16 cm³ molecule^?1 s^?1; and k(O₃ + 1NP) = (2.2 ± 0.5) × 10^?17 cm³ molecule^?1 s^?1, for pyrene, 1-hydroxypyrene and 1-nitropyrene adsorbed on silica particles. The variation in the rate constants demonstrates the strong influence of the substituent (OH or NO₂) on the heterogeneous reactivity of pyrene. The pyrene particulate concentration was also varied in order to check how this parameter may influence the experiments. Finally, oxidation products were investigated for all reactions and some were detected and identified for the first time for ozone heterogeneous reaction with pyrene adsorbed on particles.