Atmospheric Environment (v.45, #9)
Editorial board (i).
Odour emissions from a waste treatment plant using an inverse dispersion technique by Günther Schauberger; Martin Piringer; Werner Knauder; Erwin Petz (1639-1647).
The determination of the in situ emission rate of pollution sources can often not be done directly. In the absence of emission measurements, the emission rate of the source can be assessed by an inverse dispersion technique using ambient concentration measurements and meteorological parameters as input. The dispersion model used is the Austrian regulatory Gaussian model. The method is applied to a thermal waste recycling plant. Seven chemical species (butyl acetate, benzene, ethyl acetate, toluene, m/p-xylene, o-xylene and α-pinene), are identified as odorants and measured over a period of 1½ years in the prevailing wind direction leeward of the plant. The overall odour emission rate is calculated by adding the odour emission rate of all single species, using the individual odour threshold concentration. The estimated odour emission rates range between 206 and 8950 OU s−1, caused by the wide variety of the odour thresholds of the seven species. The higher value is in the upper range of odour emission rates of modern thermal treatment plants for waste.► For a thermal waste recycling plant no odour emission data were available. ► The emission rate was assessed by an inverse dispersion technique using a Gaussian model. ► Seven chemical species (butyl acetate, benzene, ethyl acetate, toluene, m/p-xylene, o-xylene and α-pinene) were identified as odorants. ► By using the odour threshold concentration, the odour emission rates were determined between 206 and 8950 OU s−1.
Keywords: Emission recalculation; Inverse dispersion technique; Odour; Emission rate; Waste treatment plant;
Trends in total ozone column over India: 1979–2008 by Ankit Tandon; Arun K. Attri (1648-1654).
Time-series decomposition analysis was performed on, (1) Multi Sensor Reanalysis (MSR) Total Ozone Column (TOC) monthly mean time-series data-set [1979–2008], and (2) Total Ozone Mapping Spectrometer (TOMS) Version 8 Overpass monthly mean time-series data-set from Nimbus 7 satellite, (TOMS N7) [1979–1993] to estimate long-term linear trends in the data to assess a scale of surface UV changes over India. Long-term trend estimation, subsequent to the removal of annual cyclic variations, for MSR TOC data-set was done over Indian region covering latitude spread 0° N – 40° N, and Longitude spread 67.5° E to 97.5° E. Trend estimates for TOMS Overpass data-sets, treated on similar lines, was done for fifteen locations over India (1°19′N to 34°04′N). Statistically significant declining trends ranging from (−) 0.8 – (−) 1.5 percent/decade were seen over Indian region above 25° N latitude in MSR TOC data-set (1979–2008). In case of TOMS N7 data-set (1979–1993), statistically significant declining trends were estimated over New Delhi (28°40′N) and Srinagar (34°04′N) with a value of (−) 2.5 and (−) 3.6 percent/decade respectively. Observed TOC decline covered 40% of total geographical area of Indian region, however rest of the Indian region (peninsular) did not show statistically any significant trend.► Statistically significant declining trends ranging from (−) 0.8 – (−) 1.5 percent/decade were observed over Indian region above 25° N latitude. ► The decline in TOC covers about 40% of geographical area of India. ► No significant decline in TOC was found below 25°N (peninsular region). ► Quantum of decline between 1979 and 2008 was smaller when compared with that estimated from 1979 to 1993. ► Area of the region over which TOC decline was observed increased from 30% to 40% of total geographical area of India, between 1979–1993 and 1979–2008.
Keywords: Total ozone column; Time series analysis; Long term trends; Satellite data;
Source and variation of carbonaceous aerosols at Mount Tai, North China: Results from a semi-continuous instrument by Zhe Wang; Tao Wang; Rui Gao; Likun Xue; Jia Guo; Yang Zhou; Wei Nie; Xinfeng Wang; Pengju Xu; Jian Gao; Xuehua Zhou; Wenxing Wang; Qingzhu Zhang (1655-1667).
Carbonaceous aerosols were measured with a semi-continuous thermal-optical OC/EC analyzer at the summit of Mount Tai (1532.7 m a.s.l) in north China during spring and summer of 2007. Non-volatile organic carbon (NVOC) and elemental carbon (EC) showed high concentrations with mean values of 6.07, 1.77 and 5.05, 0.99 μg m−3 in spring and summer, respectively. The mean concentration of semi-volatile organic carbon (SVOC) was 6.26 μg m−3 in spring and 13.33 μg m−3 in summer, contributing 51 and 72% to total organic carbon (TOC), respectively. Different measurement methods for EC were compared, and a good agreement between optical and thermal methods was found. Due to volatilization of SVOC during sampling, the integrated filter measurement without denuder and backup absorbent tended to underestimate TOC compared to semi-continuous measurement. Principal component analysis (PCA) and hierarchical cluster analysis (HCA) results indicated that the observed carbonaceous aerosols at Mount Tai were mostly contributed by the transport of aged aerosols in the planetary boundary layer (PBL) mixed with combined sources. Also, the influence of emissions from Korea was observed at Mount Tai, as well as biomass burning. Cloud processing contributed to elevated SVOC concentrations, and the formation of secondary organic aerosol (SOA) through photochemistry and cloud processing were both enhanced in summer. Clean air masses from the free troposphere reduced carbonaceous concentrations, and the regional background condition with 2.13 ± 1.05 μg m−3 of NVOC, 0.43 ± 0.29 μg m−3 of EC, and 2.40 to 6.80 μg m−3 of SVOC (for spring and summer, respectively) were suggested for the North China Plain.► Semi-continuous measurement of both semi-volatile and non-volatile carbon species. ► High carbonaceous concentration at Mount Tai in the North China Plain of China. ► Integrated filter measurement tends to underestimate TOC due to SVOC loss. ► Transport of aged aerosols in the PBL mixed with combined primary sources. ► Cloud processing and photochemistry contributed to elevated SVOC concentrations.
Keywords: Carbonaceous aerosols; Semi-volatile organic carbon (SVOC); Secondary organic aerosol (SOA); Source analysis; Mount Tai (Mt. Tai);
Agricultural PM10 emissions from cotton field disking in Las Cruces, NM by John Kasumba; Britt A. Holmén; April Hiscox; Junming Wang; David Miller (1668-1674).
Various studies have shown a relationship between elevated levels of inhalable particulate matter (PM) and agricultural practices, especially in the vicinity of agricultural fields. Airborne particle concentrations and meteorological variables were measured during nine agricultural field events on a cotton field in Las Cruces, NM in March 2008. A variety of real-time and integrated PM10 and total suspended particles (TSP) samplers were used during sampling. The field events were designed to measure particle concentrations at different heights, near (4 m) and far (20–100 m) from a disking tractor. Particle concentrations decreased with increasing distance from the ground for near-source disking events, whereas particle concentrations were almost independent of height for background events. Near-source disking event particle concentrations were 4–7 times higher than those for far-source disking and background events. Near-source disking events had PM10 emission factors ranging from 78 to 239 mg m−2, while those for far-source disking events ranged from 8 to 89 mg m−2. PM10 plume heights for near-source disking events were between 4 and 5.7 m, whereas those for far-source disking events were between 12 and 15 m. Meteorological variables were found to influence emission factors, with wind speed showing a nonlinear relationship with emission factors. No clear relationship was found between soil moisture content and emission factors probably because the range of soil moisture was small. Impactor data indicated 10–40% of the total mass of agricultural PM collected was less than 1 μm in diameter for the clay loam soil type. Vertical PM10 concentration profiles showed maxima at sampling heights between 1 and 2 m above the ground.► Real-world particle emissions from cotton field disking had 10–40% of particle mass less than 1 mm. ► Plumes from near-source sampling (4 m downwind) were elevated off the ground at 1–2 m height. ► PM10 emission factors increased with mean wind speed for both near- and far-source disking events.
Keywords: Air quality; Agricultural fields; Disking; PM10; Emission factors;
Health effects of air quality regulations in Delhi, India by Andrew Foster; Naresh Kumar (1675-1683).
This, the first systematic study, quantifies the health effects of air quality regulations in Delhi, which adopted radical measures to improve air quality, including, for example, the conversion of all commercial vehicles to compressed natural gas (CNG), and the closure of polluting industries in residential areas from 2000 to 2002. Air pollution data, collected at 113 sites (spread across Delhi and its neighboring areas) from July–December 2003, were used to compute exposure at the place of residence of 3989 subjects. A socio-economic and respiratory health survey was administered in 1576 households. This survey collected time-use, residence histories, demographic information, and direct measurements of lung function with subjects. The optimal interpolation methods were used to link air pollution and respiratory health data at the place of their residence. Resident histories, in combination with secondary data, were used to impute cumulative exposure prior to the air-quality interventions, and the effects of recent air quality measures on lung function were then evaluated. Three important findings emerge from the analysis. First, the interventions were associated with a significant improvement in respiratory health. Second, the effect of these interventions varied significantly by gender and income. Third, consistent with a causal interpretation of these results, effects were the strongest among those individuals who spend a disproportionate share of their time out-of-doors.► The study examines health effects of air quality regulations in Delhi. ► Environmental regulations in Delhi improved air quality. ► A novel methodology to compute personal exposure. ► Time-activity diary and residential history were used to compute exposure. ► Improvement in air quality show a significant improvement in respiratory health.
Keywords: Air quality regulation; Delhi; Air pollution and health; Life long exposure; Personal exposure; Lung function; Spatially detailed exposure;
Optimizing the use of on-street car parking system as a passive control of air pollution exposure in street canyons by large eddy simulation by J. Gallagher; L.W. Gill; A. McNabola (1684-1694).
An investigation was carried out to establish the effectiveness of parked cars in urban street canyons as passive controls on pedestrian pollutant exposure. A numerical model of a generic street canyon was developed using a large eddy simulation (LES) model to compare personal exposure on the footpath with and without the presence of parked cars. Three configurations of car parking systems were investigated (parallel, perpendicular and 45° parking) in addition to the influence of wind speed, wind direction and car parking occupancy. A tracer gas (CO2) was used as a representative pollutant from vehicular sources within the street canyon models. The results indicated that parked cars may act as a temporary baffle plate between traffic emissions and pedestrians on the footpath. Reductions in exposure of up to 35% and 49% were attained on the leeward and windward footpaths in perpendicular wind conditions, with parallel winds allowing up to 33% pollutant reduction on both footpaths for parallel parking. The perpendicular and 45° car parking configurations investigated proved less successful as passive controls on air pollution exposure and an increase in pollutant concentration occurred in some models. An investigation of parking space occupancy rates was carried out for parallel parked cars. The fraction of parked cars influenced the level of reduction of pollutants on the footpaths with steady reductions in perpendicular winds, yet reductions were only evident for occupancy rates greater than approximately 45% in parallel wind conditions. One negative impact associated with the parked cars study was the increase of pollutant levels on the roadway as the parked cars acted as a baffle wall, which trapped pollutants in the road. The paper underlines the potential of on-street car parking for reducing the personal exposure of pollutants by pedestrians and the optimum parking layout to achieve maximum health protection.► Investigation of 3 parked cars configurations to reduce urban pollutant exposure. ► Parallel parking provided the best layout compared to perpendicular and 45° parking. ► Parking space occupancy influences the pollution concentration on the footpath. ► Parked cars provide an alternative form to a conventional passive control.
Keywords: Street canyon; Car parking; Air pollution; Passive controls; LES;
Products of the OH radical-initiated reactions of 2-propyl nitrate, 3-methyl-2-butyl nitrate and 3-methyl-2-pentyl nitrate by Sara M. Aschmann; Ernesto C. Tuazon; Janet Arey; Roger Atkinson (1695-1701).
In the atmosphere, alkyl nitrates formed from the reactions of alkyl peroxy radicals with NO are chemically removed by photolysis and by reaction with OH radicals. Products of the gas-phase reactions of OH radicals with 2-propyl nitrate, 3-methyl-2-butyl nitrate and 3-methyl-2-pentyl nitrate at room temperature have been investigated. The products observed and quantified were: from 2-propyl nitrate, acetone (58 ± 18%); from 3-methyl-2-butyl nitrate, acetaldehyde (113 ± 39% from gas chromatographic analyses and 70 ± 25% from FT-IR analyses), acetone (55 ± 8%), and 3-methyl-2-butanone (17 ± 2%); and from 3-methyl-2-pentyl nitrate, acetaldehyde (120 ± 26% from gas chromatographic analyses and 80 ± 21% from FT-IR analyses), propanal (≤1.1%), 2-butanone (33 ± 3%), 2-methylbutanal (≤1.1%), and 3-methyl-2-pentanone (9 ± 1%), where the percentage molar yields are given in parentheses. Using these measured product yields together with predicted reaction schemes indicates that these products account for 58 ± 18%, 86 ± 15% and 63 ± 7% of the overall reaction pathways of the 2-propyl nitrate, 3-methyl-2-butyl nitrate and 3-methyl-2-pentyl nitrate reactions, respectively. The NO2 present in the −ONO2 group in these nitrates will be released in the reaction pathways leading to the observed products.► Products from reaction of OH radicals with branched alkyl nitrates indicate that NO2 is released to a large extent. ► This is because the intermediate alkoxy radicals mainly decompose to form α-nitrooxy radicals which eliminate NO2. ► Alkoxy radical reactions determine whether or not the NOx in the alkyl nitrate will be released by OH radical reaction.
Keywords: Alkyl nitrates; Hydroxyl radical; Oxides of nitrogen; Reaction products;
Analysis of local scale tree–atmosphere interaction on pollutant concentration in idealized street canyons and application to a real urban junction by Riccardo Buccolieri; Salim Mohamed Salim; Laura Sandra Leo; Silvana Di Sabatino; Andrew Chan; Pierina Ielpo; Gianluigi de Gennaro; Christof Gromke (1702-1713).
This paper first discusses the aerodynamic effects of trees on local scale flow and pollutant concentration in idealized street canyon configurations by means of laboratory experiments and Computational Fluid Dynamics (CFD). These analyses are then used as a reference modelling study for the extension a the neighbourhood scale by investigating a real urban junction of a medium size city in southern Italy.A comparison with previous investigations shows that street-level concentrations crucially depend on the wind direction and street canyon aspect ratio W/H (with W and H the width and the height of buildings, respectively) rather than on tree crown porosity and stand density. It is usually assumed in the literature that larger concentrations are associated with perpendicular approaching wind. In this study, we demonstrate that while for tree-free street canyons under inclined wind directions the larger the aspect ratio the lower the street-level concentration, in presence of trees the expected reduction of street-level concentration with aspect ratio is less pronounced.Observations made for the idealized street canyons are re-interpreted in real case scenario focusing on the neighbourhood scale in proximity of a complex urban junction formed by street canyons of similar aspect ratios as those investigated in the laboratory. The aim is to show the combined influence of building morphology and vegetation on flow and dispersion and to assess the effect of vegetation on local concentration levels. To this aim, CFD simulations for two typical winter/spring days show that trees contribute to alter the local flow and act to trap pollutants. This preliminary study indicates that failing to account for the presence of vegetation, as typically practiced in most operational dispersion models, would result in non-negligible errors in the predictions.► Trees influence pollutant concentration distribution in urban street canyons. ► Failing to account for the presence of trees may result in critical errors in model predictions. ► Building morphology and vegetation have to be analysed together. ► Analyses of data from various sources (CFD modelling, wind tunnel and monitoring stations) are necessary to produce a comprehensive picture of complex flow and dispersion phenomena within urban areas.
Keywords: Urban vegetation; Street canyon; Wind tunnel measurement; CFD simulation; City planning;
Multi-year investigations of near surface and columnar aerosols over Dibrugarh, northeastern location of India: Heterogeneity in source impacts by Mukunda M. Gogoi; Binita Pathak; K. Krishna Moorthy; Pradip K. Bhuyan; S. Suresh Babu; Kalyan Bhuyan; Gayatri Kalita (1714-1724).
The total and size segregated near surface aerosol mass concentrations obtained using a Quartz Crystal Microbalance (QCM) impactor over Dibrugarh (27.3°N, 94.6°E, 111 m amsl), in the extreme northeastern part of India, during the period 2007 to 2009 are analyzed with concurrent measurements of columnar spectral aerosol optical depths (AOD) to infer on the seasonal changes in the contribution of near surface aerosols to columnar aerosol properties. Mass concentrations within the well-mixed atmospheric boundary layer (ABL) showed systematic seasonal dependence, with annual high (∼75.6 ± 17.7 μg m−3) in February and low (∼24.8 ± 6.5 μg m−3) in June; with both the total (M t) and accumulation mode (M a) aerosol mass concentrations depicted similar variations. The accumulation mode aerosols contributed more than 50% to the total aerosol mass concentration throughout the year; accumulation mass fraction (A f = M a/M t) being highest during Dec–Feb (mean value of A f ∼ 0.87 ± 0.03) and lowest (A f ∼ 0.54 ± 0.01) in July. Examination of the AOD properties, estimated using Multiwavelength solar radiometer (MWR) observations, showed moderate to high (∼33–72%) contributions of near surface aerosols to columnar extinction during retreating-monsoon (Oct–Nov) and winter (Dec–Feb) seasons, while it was lowest (<26%) during pre-monsoon (Mar–May) season, implying large contribution by aerosols above the ABL and in the free troposphere. Trajectory clustering and concentration weighted trajectory (CWT) analysis indicated that the potential sources over the west Asian locations and that over the Indo-Gangetic Plains (IGP) significantly contribute to the total aerosol abundance over Dibrugarh during winter and pre-monsoon seasons.► The present paper covers the contribution of near surface aerosol to columnar aerosol properties. ► Significant amount of aerosols present above the atmospheric boundary layer (ABL). ► Back trajectory and Concentration Weighted Trajectory (CWT) analyses reveal the non-local potential source regions. ► The presence of large abundance of aerosols above the ABL have several implications.
Keywords: QCM; MWR; Extinction coefficient; Elevated aerosols;
The chemical mechanism of the limonene ozonolysis reaction in the SOA formation: A quantum chemistry and direct dynamic study by Tingli Sun; Yudong Wang; Chenxi Zhang; Xiaomin Sun; Wenxing Wang (1725-1731).
The ozonolysis of limonene is one of the most important processes for secondary organic aerosol formation and a detailed understanding of the atmospheric chemistry of d-limonene is highly urgent. In this paper, the reaction of d-limonene with O3 has been studied using high level molecular orbital theory. A detailed description of the possible ozonolysis mechanism in the presence of H2O or NO is provided. The main products obtained are keto-limonene, limononic acid and 7OH-lim, which are low vapor pressure compounds. On the basis of the quantum chemical information, the direct dynamic calculation is performed and the rate constants are calculated over a temperature range of 200∼800 K using the transition state theory and canonical varitional transition state theory with small-curvature tunneling effect. The four-parameter formula of rate constants with the temperature is fitted and the lifetimes of the reaction species in the troposphere are estimated according to the rate constants, which can provide helpful information to the model simulation study.► A detailed ozonolysis mechanism in the presence of H2O and NO is provided using the DFT method. ► The rate constants are calculated at a range of 200∼800 K using the CVT/SCT method. ► The four-parameter formula of rate constants and the temperature is fitted. ► The lifetimes of the species in the troposphere are estimated according to the rate constants.
Keywords: Limonene; Ozone; Formation mechanism; Quantum chemistry; Direct dynamic calculation;
Evaluating the impact of a limestone quarry on suspended and accumulated dust by Nir Bluvshtein; Yitzhak Mahrer; Amir Sandler; Giora Rytwo (1732-1739).
Rock quarrying and processing is a source of coarse and fine particulate matter, which is transported by wind to the quarry surroundings and may have an environmental impact. The current study evaluated the possible contribution of dust from such a pollution source, a limestone quarry in north Israel, during the dry summer season. Accumulated dust and total suspended particulate matter were collected following an analysis of the prevailing synoptic conditions to evaluate the background dust, its origin and expected mineralogical and chemical properties. We performed comparative gravimetric, chemical and mineralogical analyses between sites lying upwind and downwind of the limestone quarry and defined the background dust and its origin. During the summer season under the Persian trough synoptic system, mineral dust in the research area was mostly composed of material similar to the local lithosphere, mainly carbonate rocks, and thus to the quarried rock. High concentrations of some trace metals, on the other hand, were related to remote sources, as has been documented previously for the Persian trough synoptic condition. Gravimetric analysis found 300 to 400% more accumulated dust and up to 400% more total suspended particulate matter about 1 km downwind versus upwind of the quarry. Mineralogical and chemical analyses of the dust samples, and of the quarried rock, revealed that the downwind site is enriched, relative to the upwind site, in the major component of the quarried rock–calcite, and that both sites are enriched in the major components of background dust.► This study evaluated pollution of dust from a limestone quarry during dry season. ► Trace element analysis in TSP showed enrichment in elements from industrial sources. ► Downwind site is enriched in the major component of the quarried rock calcite. ► Backward trajectory analysis helped determine non-local events influencing TSP.
Keywords: Limestone quarry; Accumulated dust; Suspended dust; Mineralogy; Enrichment factor;
Assessment of motor vehicle emission control policies using Model-3/CMAQ model for the Pearl River Delta region, China by Wenwei Che; Junyu Zheng; Shuisheng Wang; Liuju Zhong; Alexis Lau (1740-1751).
In recent decades, the Pearl River Delta (PRD) region located in south China has been experiencing severe air pollution, arising from the rapid increase in industry and motor vehicles. As a major contributing source to VOCs and NOx emissions, control of vehicular emissions plays a very important role in improving regional air quality. By taking 2015 as a target year, this paper assessed the impacts of five possible motor vehicle emission control measures and a combined policy scenario on ambient air quality in the PRD region, with the use of the Model-3/CMAQ (Community Multi-scale Air Quality) model. The results show: (1) an overall decreasing pattern in SO2, NO2 and PM10 concentrations was found in central-south metropolitan areas of the PRD region for all measures, but increased O3 concentrations may occur in these areas as well. The exception to this is that a slight decrease was observed for the cases of motorcycle restriction and introduction of HEV; (2) upgrading to National IV emission standards is the most effective individual measure and can reduce daily averaged NO2 and PM10 concentrations by 11.7 ppbV and 21.3 μg m−3, respectively; but involves an increase (at maximum) of 10.3ppbV in O3 concentration. Evaluation of the combined scenario indicates that solely controlling motor vehicle emissions is not sufficient to improve PRD regional air quality significantly. O3 and PM10 concentrations under the same VOC/NOx reduction ratios exhibit differently at different locations, suggesting that integrated and location-specific pollution control strategies, considering co-control of multi-pollutants, are needed in this region in order to decrease primary and secondary pollutant concentrations simultaneously.► Projection of 2015-based PRD baseline regional emission inventory. ► Calculation of emission reduction under different vehicle control measures. ► Assessing air quality impacts of control measures using CMAQ model. ► Vehicle control can decrease primary pollutant concentrations. ► Proper VOC/NOx emission reduction ratios are important in designing regional control strategies.
Keywords: Vehicle pollution; Emission inventory; Control strategies; CMAQ model; Assessment;
Influence of solar eclipse of 15 January 2010 on surface ozone by T. Nishanth; Narendra Ojha; M.K. Satheesh Kumar; Manish Naja (1752-1758).
This study pertains to the variations observed in the mixing ratios of surface ozone, its prominent precursor NOx∗ and the meteorological parameters (solar radiation, temperature, relative humidity and wind speed) during the annular solar eclipse that occurred on 15 January 2010 at Kannur (11.9°N, 75.4°E, 5 m amsl), a tropical coastal site in the southern region of India. The solar eclipse started at 11:05 IST (IST is 5.5 h ahead of UTC), reached to the maximum obscuration at 13:20 IST and ended at 15:05 IST. The observations made at Kannur show influences of the solar eclipse phenomenon on the surface ozone and NOx∗ mixing ratios. A sharp decline in the surface ozone was observed during the eclipse, due to the decreased efficiency of the photochemical ozone formation. The NO2 ∗ levels were found to increase during the eclipse period while the NO levels remained unchanged. The eclipse induced reduction in surface ozone and enhancement in NOx∗are estimated to be 57.5% and 62.5% respectively. Reductions in the air temperature, relative humidity and wind speed were also observed during the event of solar eclipse. Simulation from a chemical box model indicates about 94% reduction in the NO2 photolysis rates during the eclipse period, which is leading to about 59% reduction in the surface ozone. Observations as well as model simulations indicate that the reduced photochemical ozone production from NO2 photolysis is possibly the main driver of ozone reduction during the eclipse at this site.► Demonstration of lower ozone due to declining solar flux during the solar eclipse. ► In contrast to the ozone, NO2 levels are found to be increasing during the eclipse. ► Air temperature, relative humidity and winds also show reductions during eclipse. ► Observed decrease (57.5%) and simulated decrease (59%) in ozone agrees well. ► Reduction in NO2 photolysis rate (94%) is the major contributor in ozone decrease.
Keywords: Solar eclipse; Surface ozone; NOx; Meteorological parameters; Box model; Kannur;
Ozone dose–response relationships for spring oilseed rape and broccoli by Maarten De Bock; Maarten Op de Beeck; Ludwig De Temmerman; Yves Guisez; Reinhart Ceulemans; Karine Vandermeiren (1759-1765).
Tropospheric ozone is an important air pollutant with known detrimental effects for several crops. Ozone effects on seed yield, oil percentage, oil yield and 1000 seed weight were examined for spring oilseed rape (Brassica napus cv. Ability). For broccoli (Brassica oleracea L. cv. Italica cv. Monaco) the effects on fresh marketable weight and total dry weight were studied. Current ozone levels were compared with an increase of 20 and 40 ppb during 8 h per day, over the entire growing season. Oilseed rape seed yield was negatively correlated with ozone dose indices calculated from emergence until harvest. This resulted in an R 2 of 0.24 and 0.26 (p < 0.001) for the accumulated hourly O3 exposure over a threshold of 40 ppb (AOT40) and the phytotoxic ozone dose above a threshold of 6 nmol m−2 s−1 (POD6) respectively. Estimated critical levels, above which 5% yield reduction is expected, were 3.7 ppm h and 4.4 mmol m−2 respectively. Our results also confirm that a threshold value of 6 nmol s−1 m−2 projected leaf area, as recommended for agricultural crops (UNECE, ), can indeed be applied for spring oilseed rape. The reduction of oilseed rape yield showed the highest correlation with the ozone uptake during the vegetative growth stage: when only the first 47 days after emergence were used to calculate POD6, R 2 values increased up to 0.476 or even 0.545 when the first 23 days were excluded. The highest ozone treatments, corresponding to the future ambient level by 2100 (IPCC, ), led to a reduction of approximately 30% in oilseed rape seed yield in comparison to the current ozone concentrations. Oil percentage was also significantly reduced in response to ozone (p < 0.001). As a consequence oil yield was even more severely affected by elevated ozone exposure compared to seed yield: critical levels for oil yield dropped to 3.2 ppm h and 3.9 mmol m−2. For broccoli the applied ozone doses had no effect on yield.► Up to 30% reduction in oilseed rape seed yield can be expected within 100 years. ► O3-induced seed yield reduction is most significantly correlated to pre-anthesis uptake. ► Broccoli yield is unaffected by moderately elevated ozone concentrations.
Keywords: Brassica napus; Brassica oleracea; Seed yield; Threshold; AOT40; POD6;
Potential impact of rainfall on the air-surface exchange of total gaseous mercury from two common urban ground surfaces by Mark C. Gabriel; Derek G. Williamson; Steve Brooks (1766-1774).
The impact of rainfall on total gaseous mercury (TGM) flux from pavement and street dirt surfaces was investigated in an effort to determine the influence of wet weather events on mercury transport in urban watersheds. Street dirt and pavement are common urban ground surfaces that concentrate many substances (eroded soil, leaf and vegetation litter, automobile debris, industrial atmospheric fallout) which can contain elevated mercury concentrations. In this study, the primary analyses included (i) observing the time series flux of TGM from pavement and street dirt following surface wetting and (ii) determining if wet deposition provides a fresh source of mercury that is available for release (emission) when applied to these surfaces. Application of de-ionized water (DI) and rainwater both induced an immediate 65% increase in TGM emission from pavement (from 0.5 to 1.4 ng m−2 h−1 [based on averages]). For street dirt, an immediate 70% increase in emission was induced following DI water application (from 3.0 to 9.0 ng m−2 h−1 [based on averages]) and an immediate 30% increase in emission following rainwater application (from 4.5 to 6.5 ng m−2 h−1 [based on averages]). Both surfaces showed continuous elevated release of TGM following the initial water application stage. There was a decrease in emission as the pavement surface dried. Despite the difference in immediate TGM emission from street dirt using both solutions, statistical evaluation indicated there was no prolonged difference. This suggests that mercury in rainwater was not available for re-emission when applied to these surfaces, at least for the time frame studied (2 h after water application). Therefore, it is likely that the elevated TGM emission following water application resulted primarily from pre-existing mercury. Removal of pre-existing mercury by water application followed a zero order process for both surfaces; however, removal rates were much different for each surface (k = 0.26 ng m−2 min−1 for street dirt; k = 0.03 ng m−2 min−1 for pavement). Results from laboratory surface washing experiments revealed only 0.1% of all available surface-bound mercury on pavement was removed by surface emission 90 min after a simulated light rainfall event (0.13 cm of rainfall).► Wetting the surfaces of pavement and street dirt increased total gaseous mercury (TGM) emission. ► Enhanced TGM emission following simulated rainfall is a result of pre-existing surface-bound mercury. ► The quantity of mercury that is emitted to the atmosphere from pavement after wetting is much smaller than the mercury load that is delivered by rainfall. ► Removal rates of pre-existing surface-bound mercury are highly different for pavement and street dirt.
Keywords: Total gaseous mercury; Urban; Rainfall; Terrestrial surface; Air-surface exchange; Runoff;
Nitrous oxide emissions from rape field as affected by nitrogen fertilizer management: A case study in Central China by Shan Lin; Javed Iqbal; Ronggui Hu; Jinshui Wu; Jinsong Zhao; Leilei Ruan; Saadatullah Malghani (1775-1779).
Agricultural soils are one of the major sources of atmospheric nitrous oxide (N2O) emission. Red soil, one of the typical agricultural soils in sub-tropical China, plays an important role in the global N2O flux emissions. To determine its N mineralization potential, a field study was conducted to assess the effect of application of nitrogen (N) fertilizer in a rape field under red soil at the experimental station of Heshengqiao at Xianning, Hubei, China. To estimate N-induced N2O flux, we examined N2O flux during the growth stages of the rape field including four treatments: fertilizer PK (N0), fertilizer NPK (60 kg N ha−1) (N1), fertilizer NPK (120 kg N ha−1) (N2), fertilizer NPK (240 kg N ha−1) (N3). There were distinct variations in soil N2O fluxes (from 0.16 to 0.90 kg N ha−1), with higher values being observed during the spring and autumn while low values were observed during winter season. Among different treatments, N fertilization significantly increased the N2O fluxes, with highest fluxes from N3 while lowest values being observed from N0 treatment. This suggested increased microbial activity in response to increased N fertilizer application. It was interesting to note that fertilizer-induced emissions decreased as the applied fertilizer amount was increased. During the whole growing season, N2O flux did not correlate with soil temperature, but it significantly correlated to other environmental variables; water-filled pore space (WFPS), soil NO3 −–N and NH4 +–N contents, which suggests the need for efficient water use and low inorganic nitrogen fertilizer management practices.
Keywords: N2O fluxes; Rape; Red soil; N fertilization;