Effects of air pollution on the searching behaviour of an insect parasitoid

To assess the impact of air pollutants on the population dynamics of herbivores, the effects of pollutants on their natural enemies including predators, parasites, and pathogens must be evaluated in addition to direct effects and indirect effects mediated via the host plant. Insect parasitoids are an important group of such natural enemies providing many examples of partial or complete biological control of pest species. This study examined the effects of air pollutants (ozone (O₃), sulphur dioxide (SO₂), and nitrogen dioxide (NO₂)) on the searching behaviour of insect parasitoids. A series of experiments comprising short-term, closed chamber fumigations of O₃, SO₂, and NO₂ (100 nl l^?1) of the braconid parasitoid (Asobara tabida) and aggregated distributions of its host larvae (Drosophila subobscura) was set up. Analysis of chamber results showed that the proportion of hosts parasitised and the searching efficiency of the parasitoids were both significantly reduced with O₃ fumigation, but not with NO₂ or SO₂ fumigations. O₃ fumigation reduced percentage parasitism by approximately 10%. Parasitoids were able to avoid patches with no hosts, both in filtered air controls and when exposed to pollutants. However in the O₃ and NO₂ treatments they appeared less able to discriminate between different host densities, suggesting that pollutants may interfere with the olfactory responses of the parasitoids. These results indicate the potential for air pollutants, particularly O₃, to negatively influence the searching behaviour of parasitoids, and hence reduce the efficiency of natural enemy control of many pest species.     

Effects of gaseous air pollutants on secondary chemistry of Scots pine and norway spruce seedlings

Plant secondary compounds have an important role in defense responses against herbivores and pathogens. This study summarises published and some unpublished data from a series of fumigation experiments where Scots pine (Pinus sylvestris L.) and Norway spruce (Picea abies (L.) Karst.) seedlings were exposed to different concentrations of gaseous air pollutants, ozone (O₃), sulphur dioxide (SO₂) or nitrogen dioxide (NO₂), in growth chambers. Concentrations of monoterpenes, resin acids and total phenolics were studied. Overall, needle monoterpenes were not affected by pollutants. Only very high level of O₃ (600 ppb) decreased concentration of some individual monoterpenes in pine needles. O₃ did not have effect on concentrations of resin acids in pine needles. In contrast, the concentration of some individual resin acids increased in O₃-exposed pine shoots and in O₃-exposed needles of one spruce clone. The highest dose of SO₂ decreased concentrations of resin acids in pine needles, but low exposure levels did not have effects. However, SO₂ had no effects on the resin acids concentrations of spruce needles, except some minor individual compounds were affected in clonal spruces. Increased concentrations of resin acids was found in pine shoots exposed to NO₂. Total phenolics of needles were not affected by pollutants. These observations suggest that among secondary compounds there is variation in sensitivity to air pollutants and genetically different trees have different responses to air pollutants.     

Casuarina and Eucalyptus response to single and multiple gaseous air pollutants

Casuarina cunninghamiana and Eucalyptus camadulensis (Egyptian var.) plants were exposed to 0.20 and 0.40 μL L^?1 O₃, SO₂ or NO₂ for 6 hr daily for 10 days. Eucalyptus plants were very sensitive to SO₂ and NO₂ and less sensitive to O₃. Casuarina plants were insensitive to the 3 gases. The rate of sorption of the 3 gases was estimated over a 10 day exposure to 0.20 μL L^?1 pollutant concentration singly and in a 3-gas mixture. Casuarina plants removed air pollutants more efficiently than Eucalyptus plants. Leaves of both species generally sorbed about the same volume of a given gas from the mixture and from the same single gas. The sorption rate over the 10 day exposure was almost constant after a higher sorption rate during the first day for both species.     

Improvements in Urban Air Quality: Case Studies from New York State, USA

Air quality levels vary over regions due to meteorological factors, proximity to sources, and local conditions (i.e., topography). The Northeast USA is subjected to pollution inputs from both local sources and those from the upwind Midwest USA that are transported by prevailing meteorological patterns. With the passage of the Clean Air Act in 1970 and the establishment of the National Ambient Air Quality Standards (NAAQS), national levels of air pollutants have declined significantly. Our study compared air quality time trends between five of the largest cities within New York State (Albany, Buffalo, New York City, Rochester, and Syracuse) and statewide means to national trends. Data were obtained from the NYS Department of Environmental Conservation (DEC) Bureau of Air Quality Surveillance for six criteria pollutants: carbon monoxide (CO), sulfur dioxide (SO₂), nitrogen dioxide (NO₂), ozone (O₃), particulate matter (PM_2.5), and lead (Pb). Regional Kendall tests found significant downward trends for each pollutant statewide from 1980 to 2007, while trends by city varied by decade and pollutant. The evaluation of historical trends of pollution in industrialized nations is useful in showing recent air quality improvements and also in the understanding what can be the result in air pollutant controls in those developing nations currently experiencing high levels of pollution.     

On Surface O3 Associated with Long-Range Transport in the Yellow Sea Region

Measurements of surface ozone (O₃) and nitrogen oxides (NO _x ) were conducted at Tae-ahn (TAP) and Chongwon (CHN) on the Korean Peninsula, during the Aerosol Characterization Experiment—Asian Pacific region (ACE-Asia) campaign, March–May 2001. The measurements provide ground-based data at a western remote site of south Korea and characterize the long-range transport of O₃ over the Yellow Sea region during spring. The mean values of O₃ and NO₂ concentration at TAP were 42 ppb and 12 ppb, respectively. The average O₃ diurnal variation of 17 ppb at TAP indicates that the loss of O₃ was not pronounced during the night. The highest NO₂ concentrations, with an average diurnal variation of 8 ppb, occurred in the afternoon at 13–15 LST. The day-to-day variation of daily O₃ concentrations at TAP is strongly influenced by the movement of synoptic scale weather patterns. In general, the O₃ concentration in a southwesterly airflow tended to increase when a moving anticyclone crossed the site, ahead of a cold front. By contrast, north-northwesterly airflows associated with the passage of a cold front bring fresh continental outflow and decrease O₃ concentrations. Surface O₃ data at TAP were classified utilizing backward trajectory analysis based on the residence time, as well as the path of the airflows, in the boundary layer (1500 m asl) over the Yellow Sea region. The results show that north-northwest continental airflows, that were transported around Lake Baikal and eastern Mongolia at an altitude of approximately 3 km at relatively high speed and came straight down at TAP, represent continental background O₃ concentrations with a mean value of 29 ppb for this period. These airflows have a short period of residence of less than one day in the boundary layer over the Yellow Sea region. In contrast, the mean O₃ value of 45 ppb was observed in regionally polluted airflows mainly passing through the east-southeast part of China and remaining for 3 days, on average, in the Yellow Sea region. These three days residence time of the regionally polluted airflows over the Yellow Sea region allowed sufficient time for photochemical O₃ formation.     

Techniques for air pollution observation from space

Air pollution problems of a scale larger than the point monitoring problem lend themselves to space observational techniques. Examples of these large scale problems are those associated with changes in the global background of gases and aerosols; potential stratospheric pollution resulting from SST operations; regional sources, pollution episodes, and large scale diffusion; and effects of pollutants on climate. These problems are discussed and observational requirements are specified. Possible remote sensing techniques for satellite monitoring are described. These include monitoring of pollutant gases and particulates by means of their absorption and scattering of radiation in both the solar spectrum range and terrestrial emission spectrum range. A discussion of potential difficulties includes the atmospheric and surface background problems, the temperature sensitivity problem in the terrestrial spectrum range, the band overlap problem, and the cloud interference problem. Recent observations from satellites and balloons are reviewed. It appears that except for H₂O, and, perhaps, O₃, measurements of the vertical profiles of atmospheric pollutant gases and aerosols from satellites will be extremely difficult. On the other hand, measurements of the total amounts (in a vertical column) of pollutant gases and aerosols do appear feasible.     

Influence of air porosity on distribution of gases in soil under assay for denitrification

 There has been concern that the measurement of gas emissions from a soil surface may not accurately reflect gas production within the soil profile. But, there have been few direct assessments of the error associated with the use of surface emissions for estimating gas production within soil profiles at different water contents. To determine the influence of air porosity on the distribution of gases within soil profiles, denitrification assays were performed using soil columns incubated with different water contents to provide air porosities of 18%, 13%, and 0% (equivalent to 62%, 73%, and 100% water-filled pore space, respectively). The soil columns were formed by packing sieved soil into cylinders which could be sealed at the top to form a headspace for the measurement of surface emissions of soil gases. Gas-permeable silicone tubing was placed at three depths (4.5, 9, and 13.5 cm) within each soil core to permit the measurement of gas concentration gradients within the soil core. Assays for denitrification were initiated by the addition of acetylene (5 kPa) to the soil column, and gas samples were taken from both the headspace and gas-permeable tubing at various times during a 46-h incubation. The results showed that at 18% air porosity, the headspace gases were well equilibrated with pore-space gases, and that gas emissions from the soil could provide good estimates of N₂O and CO₂ production. At air porosities of 13% and 0%, however, substantial storage of these gases occurred within the soil profiles, and measurements of surface emissions of gas from the soils greatly underestimated gas production. For example, the sole use of N₂O emission measurements caused three to five fold underestimates of N₂O production in soil maintained at 13% air porosity. It was concluded that the confounding influence of soil moisture on gas production and transport in soil greatly limits the use of surface emissions as a reliable indicator of gas production. This is particularly pertinent when assessing processes such as denitrification in which N gas production is greatly promoted by the conditions that limit O₂ influx and concurrently limit N gas efflux. Received: 15 January 1999     

Hydrogen Sulfide and Odor Control in İzmir Bay

The city of ?zmir on the Aegean Sea shoreline is suffering from rotten odors emitted by anoxic river mouths. Anaerobic conditions in the shallowest portion of ?zmir Bay due to industrial and domestic wastewaters as well as eutrophication products in this very calm part of the Bay are responsible for this. The inner section of the Bay is becoming shallower with sediments rich in organic matter. Aerobic digestion of organic pollutants is limited by the oxygen input and the warm climate leads to an optimal medium for anaerobic processes when anoxic conditions take over. Anaerobic digestion products are odorous gases among which H₂S with a characteristic pungent odor is most effective in this case. Sulfur containing gases are formed from sulfides and sulfates in the sediment-water interface and are released into the air. Airborne H₂S concentrations are variable as they depend on factors such as high atmospheric diffusion coefficients under changing wind direction and speed, as well as variable such as water depths, organic loadings from rivers, air and water temperatures, sulfate concentrations in sediment and water phases, pH, and Eh. This study aimed to control noxious smells by inhibiting the anaerobic sulfate-reducing bacteria at the sediment surface. To achieve this aim, pH of the sediment-water interface was increased by spreading hydrated lime. Successful lime doses were investigated in laboratory models first and were then tested and applied in the estuary and downstream segment of one of the creeks. Rates of H₂S gas emissions and aqueous H₂S levels were measured. It was noted that waterborne H₂S levels at river mouths were reduced. Odor control efficiencies of 80–96% even after 10 days of lime addition in the field experiments were obtained. Therefore, the results of this study indicated that lime application to the sediment surface is a recommended method in odor control programs.     

A Comparison of Trace Gases and Particulate Matter over Beijing (China) and Delhi (India)

Air pollution represents a significant fraction of the total mortality estimated by the World Health Organization (WHO) global burden of disease projec?t (GBD). The present paper discusses the characteristics of trace gases (O₃, NO, NO₂, and CO) and particulate matter (PM₁₀ and PM_2.5) in two Asian megacities, Delhi (India) and Beijing (China). A continuous measurement of trace gases and particulate matter are considered from 12 measuring sites in Beijing and 8 sites in Delhi. Over Beijing, the annual average of PM_2.5, PM₁₀, O₃, NO₂, and CO is, respectively, 85.3, 112.8, 58.7, and 53.4 μg/m³ and 1.4 mg/m³, and, respectively, over Delhi 146.5, 264.3, 24.7,and 19.8 μg/m³ and 1.73 mg/m³. From the spatial variations of pollutants, the concentrations of particulate matter and trace gases are observed to be much higher in the urban areas compared to the suburban areas. The higher average concentrations of PM₁₀ and PM_2.5 over Delhi and Beijing are observed during winter season compared with other seasons. The maximum diurnal variation of PM₁₀ concentration is observed during winter season over Beijing and Delhi. The comparison of trace gases shows that the O₃ concentrations during daytime are obviously higher compared with nighttime, and the highest diurnal variation of O₃ is observed during summer. The concentrations of CO are highest during winter season, and higher concentrations are observed during nighttime compared to daytime. The O₃ and CO show negative correlation over Beijing and Delhi. The negative correlation between O₃ and NO₂ is merely observed over Beijing, while CO and NO₂ concentrations, in contrast, show positive correlation over Beijing.     

Formation and Deposition of Ozone in a Red Pine Forest

Concentrations of ozone and nitrogen oxides, together with air temperature and solar radiation intensity, were measured at several heights on a tower standing through the canopy of a red pine forest in summer and in autumn. In the summer observation, the diurnal variation patterns of ozone concentration both above and below the canopy were all similar and parallel to the solar radiation intensity. Using the data collected immediately above the canopy, deviation from the Leighton relationship and variations of concentration sums [O₃] + [NO] and [NO₂] + [NO] were examined, and as a result, it was supposedthat ozone was photochemically formed there in the daytime, probably because hydrocarbons emitted from pine trees broke the photostationary state among ozone and nitrogen oxides. The vertical temperature profile exhibited an inversion at the leaf-layer, which must have hindered vertical mixing of the air and made the trunk space more or less isolated from the upper atmosphere. These observations led to an idea that the similarity of the ozone variation pattern at every height was caused by the photochemical formation that proceeded simultaneously above and below the canopy rather than by vertical transport. Such situations of ozone formation were supported by observation of two maximums in the ozone vertical profile, one immediately above the canopy and another in the trunk space. Another feature of the ozone profile was a deep minimum in the leaf layer, which indicated ozone deposition onto leaf surfaces. This study thus revealed concurrence of ozone formation and deposition, and left two potentially important implications worthy of further investigation: (1) a forest is not always a sink but can be a source of ozone in sunlit conditions, and (2) deposition of ozone to trees can take place not only from outside but also from inside of a forest. In the autumn observation, however, the ozone formation was barely recognizable above the canopy and no longer found in the trunk space; in addition, the ozone concentration minimum in the leaf layer disappeared, suggesting that the deposition or removal was dependent on temperature.     

Chemical reactions of mercury in combustion flue gases

Atmospheric Hg is present in different physical and chemical forms, which determine its atmospheric transformation and transport capacities. The chemistry of Hg in flue gases is thus of importance for the deposition pattern around point source emissions. In order to apply Hg cleaning methods in flue gases its speciation is also of importance. To investigate this under realistic conditions, a 17 kW propane fired flue gas generator was used, while the kinetics of specific Hg reactions were investigated in a continuous flow reactor. Elemental Hg is readily oxidized by Cl2 and HCl both at room and at elevated temperatures (up to 900 °C) but not by NH₃, N₂O, SO₂ or H₂S. It reacts with O₂ if a catalyst, such as activated carbon, is present. A slow reaction between Hg and NO₂ has also been noted.     

Schwefeldioxid,Schwefelwasserstoff, nitrose Gase und Ammoniak als ausschließliche S- bzw. N-Quellen der höheren Pflanze

Sulphur dioxid, hydrogen sulphate, nitrous gases, and ammonia as sole source of S and N for higher plants Long duration gasing experiments using SO₂, H₂S, nitrous gases and NH₃, showed, that higher plants can use these gases as only source of S or N respectively, without affecting their normal growth during the whole vegetation period. The sulphur and nitrogen of these high oxidized or high reduced gas forms were taken up by the plants and were also translocated to the roots. The assimilation of sulphur, given as SO₂, was more intensive than that given as H₂S. The uptake of nitrogen, given as ammonia, was higher than that given as nitrous gases.     

Oxygen and redox potential gradients in the rhizosphere of alfalfa grown on a loamy soil

Oxygen (O₂) supply and the related redox potential (E_H) are important parameters for interactions between roots and microorganisms in the rhizosphere. Rhizosphere extension in terms of the spatial distribution of O₂ concentration and E_H is poorly documented under aerobic soil conditions. We investigated how far O₂ consumption of roots and microorganisms in the rhizosphere is replenished by O₂ diffusion as a function of water/air‐filled porosity. Oxygen concentration and E_H in the rhizosphere were monitored at a mm‐scale by means of electroreductive Clark‐type sensors and miniaturized E_H electrodes under various matric potential ranges. Respiratory activity of roots and microorganisms was calculated from O₂ profiles and diffusion coefficients. pH profiles were determined in thin soil layers sliced near the root surface. Gradients of O₂ concentration and the extent of anoxic zones depended on the respiratory activity near the root surface. Matric potential, reflecting air‐filled porosity, was found to be the most important factor affecting O₂ transport in the rhizosphere. Under water‐saturated conditions and near field capacity up to –200 hPa, O₂ transport was limited, causing a decline in oxygen partial pressures (pO₂) to values between 0 and 3 kPa at the root surface. Aerobic respiration increased by a factor of 100 when comparing the saturated with the driest status. At an air‐filled porosity of 9% to 12%, diffusion of O₂ increased considerably. This was confirmed by E_H around 300 mV under aerated conditions, while E_H decreased to 100 mV on the root surface under near water‐saturated conditions. Gradients of pO₂ and pH from the root surface indicated an extent of the rhizosphere effect of 10–20 mm. In contrast, E_H gradients were observed from 0 to 2 mm from the root surface. We conclude that the rhizosphere extent differs for various parameters (pH, Eh, pO₂) and is strongly dependent on soil moisture.     

Chemical Composition of Air, Soil and Vegetation in Forests of the Silesian Beskid Moutains, Poland

For the first time concentrations of trace nitrogenous (N) air pollutants, gaseous nitric acid (HNO₃), nitrous acid (HNO₂), ammonia (NH₃), and fine particulate nitrate (NO₃) and ammonium (NH₄), were measured in the montane forests of southern Poland. Determinations were performed in two forest locations of the Silesian Beskid Mountains in the western range of the Carpathian Mountains, and in an industrial/urban location in Karowice, Poland. The measurements performed in summer 1997 with honeycomb denuder/filter pack systems showed elevated concentrations of the studied pollutants. These findings agree with the low carbon/nitrogen (C/N) ratios and the results of ¹⁵N analyses of soil and moss samples. High concentrations of N air pollutants help to explain previously determined high levels of NO₃ and NH4 deposition to Norway spruce (Picea abies Karst.) canopies in these mountains. Ambient concentrations of sulfur dioxide (SO2) and ozone (O3) were elevated and potentially phytotoxic. Deficiencies of phosphorus (P) and magnesium (Mg) in Norway spruce foliage were found while concentrations of other nutrients were normal.     

SO2 Transformation in controlled atmosphere leading to the production of aerosol particles

The photochemical transformation of SO₂ and the generation of aerosol particles are investigated in a variety of atmospheres, with and without initial aerosols, in clean and polluted air, and with various pollutants. The pollutants in addition to the SO₂ include O₃, NO, NO₂ and water vapor in a variety of combinations. The most striking finding is, that only with the combination of SO₂, NO₂, and H₂O is the aerosol particle production large.     

Distributed Modified Bowen Ratio method for surface layer fluxes of reactive and non-reactive trace gases

Modified Bowen ratio technique was used in a horizontally distributed form to determine turbulent fluxes of CO₂, H₂O, O₃, NO and NO₂ over a semi-natural grassland site in North-Eastern Germany. The applicability of the distributed variation of the Modified Bowen Ratio technique was proven prior to the calculation of trace gas fluxes. Turbulent NO fluxes were compared to fluxes up-scaled from laboratory measurements of biogenic NO emission from soil samples, which have been taken at the field site. The NO fluxes up-scaled from laboratory measurements were slightly larger than the fluxes observed in the field. However, both NO fluxes agreed within a factor of two. Under suitable night time conditions, we performed a detailed comparison of turbulent fluxes of CO₂ and O₃ with fluxes derived by the boundary layer budget technique. While there was agreement between these fluxes in a general sense, specific deviations were observed. They could be attributed to different footprint sizes of both methods and to in situ chemistry within the nocturnal boundary layer.     

Observations of Aitken nuclei and trace gases in different environments in India

Surface measurements of Aitken nuclei have been made at a few representative environments in India. The periods of measurements have ranged from a few days to a few years depending upon the place of measurement. Aircraft measurements of Aitken nuclei were made at one of the locations during three successive monsoon periods. During part of the time simultaneous measurements were made of the trace gases SO₂, NH₃, NO₂, and O₃. The study presents the seasonal and diurnal variation of Aitken nuclei in the different environments and their association with the trace gas concentrations.     

Effect of water vapor and nitrogen oxides upon the ozone layer

A theoretical meridional model of the O₃ layer is presented. Two-dimensional transport by eddies and mean motion is considered together with photochemical reactions involving O, N, and H. The model is used to evaluate the effect of increased contents of H₂O and NO_x in the stratosphere. It is found that a doubling of stratospheric humidity will reduce the total amount of O₃ by less than 1 %, while a doubling of NO_x will result in an 18 % reduction for middle latitudes and summer. A 10 % increase in NO_x will reduce the total O₃ by about 2.8%. The relations between UV radiation and total O₃ are described, in particular, for wavelengths of biological interest (290 to 320 nm). A 1% decrease in total O₃ will result in a 2 % increase in erythemogenic UV radiation.