Spatial Distribution Of NO Research Articles

NOx generation in marine dual-fuel engines: Effects of ammonia blending ratio and spark ignition timing

Ammonia application in marine engines can effectively mitigate greenhouse gas emissions. However, engines powered by ammonia produce considerably higher levels of NOx emissions compared to conventional fuel engines. In the present study, a combustion model for the marine dual-fuel engine fueled with natural gas and ammonia has been established using the CONVERGE software. The nitrogen element-tracking method is employed in the engine combustion simulation. This study aims to investigate the effects of ammonia blending ratio (XNH3 = 0% ∼ 50%) and spark ignition timing (SIT = −20 °CA ATDC ∼ −40 °CA ATDC) on the emission characteristics and spatiotemporal distribution of nitrogen-based pollutants under lean-burn and stoichiometric-burn conditions. The results indicate that as the XNH3 increases, total NOx emissions decrease at stoichiometric-burn conditions, while it initially increases and then decreases at lean-burn conditions, reaching a peak of 3760 ppm at XNH3 = 30%. Besides, fuel NO emissions are predominant at lean-burn conditions, whereas at stoichiometric-burn conditions, thermal N*O emissions are predominant. Additionally, as the SIT advances, total NOx emissions initially decrease and then remain unchanged, reaching a minimum at −35 °CA ATDC, and it gradually increases at lean-burn combustions. Furthermore, the spatial distribution of NO at CA50 illustrates that fuel NO is primarily concentrated at the flame front, while thermal N*O predominates in the high-temperature burned region. N2O is observed in the low-temperature region near the cylinder wall during the expansion stroke. Moreover, fuel NO is primarily produced by ammonia's decomposition with OH radicals. There are three dominant reactions for the formation of NO: HNO→NO, NH→NO, and N→NO. The coupling mechanism of carbon and nitrogen elements is achieved by H2CN and HCN radicals.

Effects of residence time on the NOx emissions of premixed ammonia-methane-air swirling flames at elevated pressure

In this study, a bespoke single-stage swirl burner was used to experimentally investigate the effects of residence time on emissions from premixed ammonia-methane-air flames. The residence time was altered in two ways: by modifying the combustion chamber's length or by modifying the swirl number. Exhaust emissions of O2, CO2, CO, NO, NO2, and N2O were measured at an absolute pressure of 2 bar for equivalence ratios between 0.50 and 0.95 and ammonia fractions in the fuel blend between 0 and 100%. Spatial distributions of NO and OH radicals were also imaged using PLIF inside the combustion chamber at different heights above the nozzle. Data shows that increasing residence time can further advance chemical reactions, as evidenced by a reduction in O2 concentration in the exhaust. Increasing the swirl number reduces emissions of NO, NO2, and N2O more efficiently than tripling the chamber's length. However, a decrease in the combustion efficiency may be responsible for a fraction of this NOx reduction when the swirl number is increased for some equivalence ratios. NO emissions are not modified when the chamber's length is increased, which is consistent with the fact that the NO-LIF signal does not decay when the distance from the nozzle increases. Therefore, NO formation is somehow restricted to within the main reaction zone of the swirling flame, that is, the zone whose height does not exceed 60 mm for this burner. Conversely, tripling the chamber's length reduces the concentrations of NO2 and N2O. This reduction is not reflected in a measurable increase in NO concentration because NO is present in much larger quantities than NO2 and N2O in flames examined here. Consistent with the fact that OH promotes NO formation via fuel-NOx pathways, a positive correlation is found between NO- and OH-LIF intensities.

Methane Gas Cofiring Effects on Combustion and NO x Emission in 550 MW Tangentially Fired Pulverized-Coal Boiler.

A shift from coal to liquefied natural gas for electricity generation can mitigate CO2 emissions and respond to the intermittent and variable characteristics of renewable energy. With this objective, numerical simulation was performed in this study to determine the optimal position of the methane injector and evaluate the achievable reduction in NOx emissions before applying methane cofiring to an existing 550 MW tangentially fired pulverized-coal boiler (Boryeong Unit 3). The combustion and NOx reduction in the furnace were intensively analyzed based on the methane cofiring rate (up to 40%). The optimal position of the methane injector was found to be inside the oil port based on the spatial distribution of NOx and the stoichiometric ratio along the furnace height. The NOx reduction rate was logarithmically proportional to the methane cofiring rate, and compared to the base case, a 69.8% reduction was achieved at the 40% cofiring rate. In addition, the fraction of unburned char at the boiler outlet was equivalent to that of the existing boiler as the increase in the flow rates of the close-coupled and separated overfire air improved fuel and air mixing. Simultaneously, methane cofiring led to a reduction in the total fuel loss and CO emissions. Finally, this study showed that the recommended optimum cofiring rate was 20% based on the furnace exit gas temperature. Under the 20% methane cofiring condition, the boiler achieved a 57.3% reduction in NOx emissions and a 7.4% improvement in fuel loss.

Seasonal and spatial variations of N, P, K and Cd concentrations in water of the Mahakanumulla Cascade in the Dry zone of Sri Lanka

Systematic work on water quality aspects, particularly on the accumulation and fluctuation of plant nutrients and heavy metals, has not being carried out at the Mahakanumulla tank cascade in the dry zone of Sri Lanka. Therefore, the main objective of this research was to study the seasonal changes of the concentration of major plant nutrients viz., Nitrogen (NO 3- ), Phosphorus (PO4 3- ), Potassium (K + ), and heavy metal Cadmium (Cd +2 ) in water along the cascade system. The concentrations of NO 3- , PO4 3- , K + and Cd +2 in water samples showed significant spatial and temporal variations over the study period and showed a bimodal pattern. The highest concentrations of the measured parameters were observed in months of April and May in the Yala season. Low nutrient concentration observed in the Maha season could be due to dilution effect caused by the comparativelyhigh volume of tank water. Spatial distribution of NO 3 - , PO4 3- , K + and Cd +2 concentrations in the water of three sampling locations of each paddy tract showed a significant increasing trend from the first sampling point to third point of the paddy field. Tropical Agricultural Research Vol. 24 (3): 279 – 288 (2013)

Nitric oxide mediates strigolactone signaling in auxin and ethylene-sensitive lateral root formation in sunflower seedlings

Strigolactones (SLs) play significant role in shaping root architecture whereby auxin-SL crosstalk has been observed in SL-mediated responses of primary root elongation, lateral root formation and adventitious root (AR) initiation. Whereas GR24 (a synthetic strigolactone) inhibits LR and AR formation, the effect of SL biosynthesis inhibitor (fluridone) is just the opposite (root proliferation). Naphthylphthalamic acid (NPA) leads to LR proliferation but completely inhibits AR development. The diffusive distribution of PIN1 in the provascular cells in the differentiating zone of the roots in response to GR24, fluridone or NPA treatments further indicates the involvement of localized auxin accumulation in LR development responses. Inhibition of LR formation by GR24 treatment coincides with inhibition of ACC synthase activity. Profuse LR development by fluridone and NPA treatments correlates with enhanced [Ca2+]cyt in the apical region and differentiating zones of LR, indicating a critical role of [Ca2+] in LR development in response to the coordinated action of auxins, ethylene and SLs. Significant enhancement of carotenoid cleavage dioxygenase (CCD) activity (enzyme responsible for SL biosynthesis) in tissue homogenates in presence of cPTIO (NO scavenger) indicates the role of endogenous NO as a negative modulator of CCD activity. Differences in the spatial distribution of NO in the primary and lateral roots further highlight the involvement of NO in SL-modulated root morphogenesis in sunflower seedlings. Present work provides new report on the negative modulation of SL biosynthesis through modulation of CCD activity by endogenous nitric oxide during SL-modulated LR development.

Infertility and its relationship with NO2pollution in Iran from 2009 to 2012

Background: National Institute of Environmental Health Sciences scientists show that long-term exposure to air pollutants increases the risk of infertility. NO 2 factor is considered as one of the underlying causes of infertility diseases. This study aimed to determine the association of infertility diseases documented in medical records and NO 2 accumulation in Iran. By plotting the prevalence and spatial distribution maps, important differences from different points can be observed. Materials and Methods: In this study, the first challenge was to collect some relevant information. In this connection, the authors managed to gain access to data concerning infertility in Iran. The data, which had been collected by Country Health Centre, provided information from 2009 to 2012. To measure spatial distribution of NO 2 pollutions we used ozone monitoring instrument. Using geographic information system (GIS), the researchers drew the map of the spatial distribution of infertility in the country and then we used Neural Network model (NN) to obtain relation between air-pollution and infertility data, that NO 2 data obtained using zonal statistics in GIS. Results: Space with tracing the distribution of infertility diseases was scattered based on the distribution of NO 2 pollution in the points is an important part of this type of diseases in Iran where air-pollution was more abundant. Finding: The findings of this study emphasis on the importance of preventing the exposure to air-pollution, and to control air-pollution producing industries, to improve work environmental health, and to increase the health professionals and public knowledge in this regard. Conclusion: The analysis revealed to what extent NO 2 explained the observed infertility incidence values. NN analyses were performed (at the 99% confidence level in training data and 88% in validation).

In-situ spectroscopic monitoring of Jatropha oil combustion properties

In-situ monitoring of chemical species emitted from the combustion of Jatropha oil in a practical Semawar burner were performed by means of several spectroscopic diagnostics. A practical burner commonly used in Indonesia having a built-in preheating system, called semawar, used for illumination purposes with the combustion of Jatropha oil. Non-intrusive two-dimensional (2-D) distributions of flame temperature were obtained using a thermal video camera. The experimental results showed the flame temperatures to range from 500 to 1400 °C. Chemical species generated from within the combustion zone were also determined in the Ultraviolet–visible (Uv–Vis) range from the spontaneous emission spectra of the flame. Spatial distribution of NO, C2 and OH were identified from the spectra. The 2-D distribution emission intensity visualized and recorded for NO, C2 and OH revealed high temperatures close to the root of the flame that rapidly dispersed radially outwards to provide very high temperatures over much larger volume at downstream locations. The radial stretch of the reaction zone is important for improved performance of the burner with light emission form a much wider zone. In addition, in-situ monitoring of CO2 emission of Jatropha oil was performed by using infrared (IR) spectroscopy. The presence of CO, H2O and NO were also investigated in this research. Moreover, 2D distribution of CO2 emission intensity was also visualized using an IR camera.

Spectroscopic Observation of Chemical Species From High-Temperature Air Pulverized Coal Combustion

In situ monitoring of chemical species from the combustion pulverized coal in high-temperature air is examined using several different spectroscopic diagnostic at different equivalence ratios. Two-dimensional (2D) distributions of flame temperature were obtained using a thermal video camera. The experimental results showed the temperatures to range from low to 1400 °C under various conditions of fuel-lean, stoichiometric, and fuel-rich. The highest temperature and flame stability were obtained under fuel-lean combustion condition. The chemical species generated from within the combustion zone were analyzed from the spontaneous emission spectra of the flame in the Ultraviolet–visible (UV-Vis) range. The spatial distribution of NO, OH, and CN were identified from the spectra. The 2D distribution of emission intensity visualized and recorded for NO, OH, and CN revealed high-temperatures close to the root of the flame that rapidly dispersed radially outward to provide very high temperatures over a much larger volume at further downstream locations of the flame.

Evaluation of air quality by passive and active sampling in an urban city in Turkey: current status and spatial analysis of air pollution exposure

Concentrations of air pollutants, nitrogen dioxide (NO(2)), sulfur dioxide (SO(2)), ozone (O(3)), particulate matter (PM(2.5) and PM(10)), trace metals, and polycyclic aromatic hydrocarbons (PAHs) were measured in 2008 and 2009 in the city of Eskişehir, central Turkey. Spatial distributions of NO(2), SO(2), and ozone were determined by passive sampling campaigns carried out during two different seasons with fairly large spatial coverage. A basic population exposure assessment was carried out employing Geographical Information System techniques by combining population density maps with pollutant distribution maps of NO(2) and SO(2). It was found that 95 % of the population is exposed to NO(2) levels close to the World Health Organization guideline value. Regarding SO(2), a large proportion of the population (83 %) is exposed to levels above the WHO second interim target value. Concentrations of all the pollutants showed a seasonal pattern increasing in winter period, except for ozone having higher concentrations in summer season. Daily PM(10) and PM(2.5) concentrations exceeded European Union limit values almost every sampling day. Toxic fractions of the measured PAHs were calculated and approximately fourfold increase was observed in winter period. Copper, Pb, Sn, As, Cd, Zn, Sb, and Se were found to be moderately to highly enriched in PM(10) fraction, indicating anthropogenic input to those elements measured. Exposure assessment results indicate the need for action to reduce pollutant emissions especially in the city center. Passive sampling turns out to be a practical and economical tool for air quality assessment with large spatial coverage.

Monitoring of atmospheric nitrogen dioxide by long-path pulsed differential optical absorption spectroscopy using two different light paths

Measurements of the local distribution of atmospheric nitrogen dioxide (NO(2)) by long-path pulsed differential optical absorption spectroscopy (LP-PDOAS) in Tokyo during August 2008 are presented. Two LP-PDOAS systems simultaneously measured average NO(2) temporal mixing ratios along two different paths from a single observation point. Two flashing aviation obstruction lights, located 7.0 km north and 6.3 km east from the observation point, were used as light sources, allowing spatiotemporal variations of NO(2) in Tokyo to be inferred. The LP-PDOAS data were compared with ground-based data measured using chemiluminescence. Surface wind data indicated that large inhomogeneities were present in the spatial NO(2) distributions under southerly wind conditions, while northerly wind conditions displayed greater homogeneity between the two systems. The higher correlation in the NO(2) mixing ratio between the two LP-PDOAS systems was observed under northerly wind conditions with a correlation factor R(2) = 0.88. We demonstrated that the combined deployment of two LP-PDOAS systems oriented in different directions provides detailed information on the spatial distribution of NO(2).

NO x emission characteristics and aerodynamic structure of a self-recirculation type burner for small boilers

To meet the coming, more stringent NO x emission standards for small boilers, a self-recirculation type burner, in which a fresh air is injected through eight nozzles, arrayed peripherally around a liquid fuel-spray nozzle, while the hot burned gas is recirculated within the furnace and entrained into the injected air streams has been experimentally investigated. The flowfield has been determined with a PIV system and spatial distributions of NO x , temperature, O 2 and CO have been determined with use of chemi-luminescence, thermocouple, magnetic pressure type analysis, and non-dispersive infrared analysis, respectively. 2-D flame chemi-luminescence images have been obtained by an ICCD camera synchronized with the PIV system. Results show that the burned gas is recirculated in the furnace and successively entrained into the air streams. As a result, NO x emission is drastically decreased. In the present prototype burner, the amount of a recirculating gas entrained into the air streams attains 50% the fresh air by volume and the NO x level is decreased to 22 ppm from its original value of 108 ppm without recirculation. Further measurements show that besides the recirculating flow outside the air nozzles, another recirculating flow is induced around the center axis inside the injected air streams. Combustion is stabilized around this inner recirculation zone. With an increase in the air flow rate while keeping the spraying fuel flow rate constant, this inner recirculation zone expands and its centre approaches the fuel nozzle. The evaporation of liquid fuel is promoted and a blue flame zone is established. The NO x level is further reduced to 18 ppm when the air excess ratio is increased to 1.6. Thus, the present, simple device of self-recirculation type burner can successfully reduce NO x emission without great cost and space.

自己循環型低NO_xバーナの流れ場計測と燃焼性能(熱工学,内燃機関,動力など)

A self-recirculation type low NO_x burner, in which a fresh air is injected through a nozzle with a high velocity speed and a hot burned gas is involved into the air stream through a recirculation space, has been experimentally investigated. The flowfield has been determined with a PIV system and spatial distributions of NO_x, temperature, CO and O_2 have also been determined in a test furnace. Results show that a recirculation of a burned gas is indeed induced outside the air nozzle and the NO_x level is significantly reduced. In the present burner, the amount of a recirculating burned gas attains 50% the fresh air and the NO_x level is decreased below 20ppm. Further measurements indicate that a recirculating flow is also induced inside the air nozzle and combustion is stabilized around a stagnant region of this recirculation flow. With an increase in the air flow this inner recirculation zone expands and its centre approaches the fuel nozzle. The evaporation of liquid fuel is promoted, resulting in formation of blue flame. The NO_x level is further reduced to 18ppm for the air excess ratio of 1.6 in the present burner system.

Analysis of NO structure in a methane–air edge flame

We present computations of a methane–air edge flame stabilized against an incoming flow mixing layer, using detailed methane–air chemistry. We analyze the computed edge flame, with a focus on NO-structure. We examine the spatial distribution of NO and its production/consumption rate. We investigate the breakdown of the NO source term among the thermal, prompt, N2O, and NO2 pathways. We examine the contributions of the four pathways at different locations, as the edge flame structure changes with downstream distance, tending to a classical diffusion flame structure. We also examine the dominant reaction flux contributions in each pathway. We compare the results to those in premixed, non-premixed, and opposed-jet triple flames.

The effect of combustion chamber geometry layout on combustion and emission

In this paper some results concerning the combined effect of the tumble flow and combustion chamber geometry layout variations on flame front shape and its propagation through homogenous mixture of isooctane and air are presented. Spatial distributions of NO in different combustion chamber geometries are presented as well. The basic combustion chamber geometry layout considered consists of the flat head with two vertical valves and a cylindrical bowl subjected to variations of depth and squish area. All results presented were obtained by dint of multidimensional modeling of reactive flows in arbitrary geometry with moving objects and boundaries with modified KIVA3 and KIVA3V source codes. Two additional computer codes were applied to generate boundary conditions for KIVA3V calculations with moving valves. The AVL TYCON code was used for the calculation of valve lift profiles, and AVL BOOST code was used for the calculation of relevant data set in the valve regions. Different combustion chamber geometry layouts generate different levels of squish, and the combustion effects in essence depend on the interaction of that flow with tumble. It was found that for particular combustion chamber shapes with different diameter/depth aspect ratios entirely different flame front shapes and propagation velocities were encountered primarily due to variations of fluid flow patterns in the vicinity of top dead center.

Evaluation of the best compromise between the urban air quality monitoring resolution by diffusive sampling and resource requirements

The need to collect data representative of overall urban pollution is all-important in order to monitor the population exposure. High spatial resolution monitoring using diffusive samplers allows studying of the urban pollutant distribution, thus enabling deeper investigation of their generation and diffusion mechanisms. Nevertheless, such a monitoring campaign has a certain cost. In this study we point out how to find the best compromise between the number of necessary measurements and the affordable costs for monitoring campaigns. We also describe an innovative method for the proper design of a fixed urban monitoring network by means of preliminary high spatial resolution campaigns using diffusive samplers. Four European capital cities (Dublin, Madrid, Paris and Rome) were monitored six times, each time for seven days. Benzene, toluene, ethylbenzene, xylenes (BTEX) and NO(2) concentrations were measured at 146 sites in Dublin, 293 in Madrid, 339 in Paris and 290 in Rome. Multiscale grids have been drawn which ranged in mesh size from 500 m to 2 km. The statistical processing of data produced a twofold result: the creation of isoconcentration maps with geostatistical procedures, and an algorithm aimed at locating the minimum number of sampling sites where the fixed monitoring stations should be placed. Average urban levels estimated on the basis of these selected sites differ by less than 8% from those calculated on the whole populations of the sampled points. The aim of this work is to investigate how far the resolution of a monitoring campaign of urban pollution by diffusive sampling can be reduced, thus making the monitoring less expensive in terms of human and financial resources, while preserving the same quality of the results that could be achieved with a higher resolution. We found that there is no significant loss of information when the resolution of the monitoring grid for BTEX is lowered to a mesh size of 1.85 km, that is a sampling site each 3.4 km(2), and that the minimum number of sampling sites to be used is N = 0.29 A, where A is the urban surface to be monitored (in km(2)). As the spatial distribution of NO(2) is less sensitive to the distance from the emission source than that of BTEX, this relationship could be retained as a valid lower limit for the mesh grid size also for NO(2) monitoring.

街路樹がストリートキャニオン内の気流分布,空気汚染,歩行者空間の温熱快適性に及ぼす影響の検討 : 仙台市中心市街地の夏季の温熱・空気環境実測(その1)

This study aims to clarify the effects of roadside trees on turbulent airflow, air pollutant diffusion and pedestrian thermal comfort within street canyons in the central part of Sendai city, Japan. The detailed measurements were carried out within Jozenji-street in the summer of 2004. Measurements within Hirose-street were also conducted for comparison. Characteristics of flow pattern and distributions of turbulence quantities were investigated, and time-variations of spatial distributions of NO_X concentration and thermal environment, i.e. air temperature, globe temperature, air humidity and SET were shown. In Jozenji-street, many trees were planted on sidewalk and central walkway, and the density of trees was much higher than that in Hirose-street. The effects caused by roadside trees showed complex results which clearly improved thermal environment but also increased NO_X concentration simultaneously.

Spatial Variability and Transport of Nitrate in a Deep Alluvial Vadose Zone

Little empirical evidence exists about the spatial distribution of NO 3 –N in deep vadose zones and about the associated fate and transport of NO 3 –N between the root zone and the water table. We investigated NO 3 –N occurrence in a deep alluvial vadose zone and its relation to geologic site characteristics, hydraulic properties, and fertilizer application rates via an intensive three-dimensional core-sampling campaign beneath an irrigated orchard in semiarid Fresno County, California. Statistical and geostatistical analyses were used to determine spatial variability of NO 3 –N and water content, to estimate total NO 3 –N mass in the vadose zone beneath each of three fertilizer treatments, and to compare NO 3 –N occurrence with that predicted from standard agronomic analysis of N and water flux mass balances. Vadose zone NO 3 was highly variable and lognormally distributed. Fertilizer treatment had a significant effect on NO 3 –N levels in the vadose zone. In all cases, deep vadose zone N mass estimated by kriging measured data totaled only one-sixth to one-third of the mass predicted by the N and water flux mass balance approach. Vadose zone denitrification estimates could not account for this discrepancy. Instead, the discrepancy was attributed to highly heterogeneous flux conditions that were not accounted for by the mass-balance approach. The results suggest that spatially variable vadose zone flow conditions must be accounted for to better estimate the potential for groundwater NO 3 loading.

Nitric oxide detection in turbulent premixed methane/air flames

Investigations of the nitric oxide formation mechanisms of turbulent premixed methane/air flames, with regard to turbulence properties and equivalence ratio, are presented. An atmospheric burner with perforated turbulence generating grids allowed the realization of different turbulent flow conditions ( Re = 8.5 × 10 3–1.7 × 10 4, u′/ s L = 0.8–8.0), which were measured by PIV. Planar LIF was used to detect the OH radical (as a tracer for the flame front) and to visualize the distribution of NO in a two-dimensional area for the whole flame up to far downstream positions. A chemiluminescence detection (CLD) of the NO concentration in the post-flame gases was employed to quantify the NO-LIF measurements. The influence of the equivalence ratio on the spatial distribution of NO was similar to numerical predictions for laminar flames, while variations of turbulence conditions played a rather minor role. The statistical evaluation of local flame front locations enabled the determination of their fluctuation region and its probability distribution. Comparing ensemble-averaged and distribution width of the flame location along the burner axis with the spatial distribution of NO assisted in the understanding of the relative contributions of prompt- and thermal-NO formation paths for different values of the equivalence ratio and turbulence intensity in turbulent premixed flames. Furthermore, qualitative single shot NO-LIF measurements showed structural features, resembling those of the instantaneous turbulent flame front.

Environmental Impact Assessment For Oman LNG Expansion Project: NO 2 Air Quality Analysis with A Proposal For A Third Train

Oman entered the LNG market (liquefied Natural Gas) in April 2000 with the first shipment to South Korea. Oman LNG plant is currently producing 6.6 million metric tonne per annum from two trains. However, there are plans for expansion of the plant to increase its existing capacity by adding one more gas liquefaction train (train 3). The purpose of this study is to assess the potential environmental air quality impacts arising from the construction and operation of train 3. The article contains a baseline-survey of the existing environment, the proposed project description and prediction of the possible future air quality impacts of this project on the existing community and its environment. Recognizing that nitrogen dioxide (NO 2 ) may be the primary air contaminant released from Oman LNG plant, this work has been designed with emphasis on this pollutant. The environmental impact assessments including an air quality analysis in terms of NO 2 has been conducted by using the Industrial Source Complex Short-Term (ISCST) dispersion model. The results are presented in contour map forms to determine the spatial distribution of NO 2 to be produced when train 3 is operating. The study indicates that the highest NO 2 concentration values will be observed in the summer months (June, July and August). Generally, the predicted concentrations are found much lower than the permissible limit values with the maximum ground level concentrations being found much closer to the plant. On the basis of this study it can be stated that the Oman LNG plant, after the addition of train 3, is not likely to cause significant deterioration in air quality.

Aerosol NO-3 and 210Pb distribution over the central-eastern Arabian Sea and their air-sea deposition fluxes

The concentrations of NO − 3 , SO 2− 4 and 210 Pb have been measured in the marine boundary layer over the central-eastern Arabian Sea to investigate the sources of NO − 3 to this region and its deposition flux to the sea surface. Bulk aerosol samples were collected during April – May (intermonsoon) 1994, July – August (monsoon) 1995, 1996 and February – March (winter) 1995, 1997. The NO − 3 and 210 Pb concentrations, during the intermonsoon and winter, ranged from 0.4 to 4.1 μg m −3 and (12.3 to 70.3) × 10 −3 dpm m −3 , respectively; with systematically higher concentrations during the winter. Their concentrations were the lowest, 0.2 to 0.8 μg m −3 and (4.0 to 17.6) × 10 −3 dpm m −3 , respectively, during monsoon. The seasonal and spatial distributions of NO − 3 and 210 Pb in the aerosols show a significant positive correlation and bring to light the dominant ro le of continental sources in the chemistry of aerosols over the Arabian Sea. The NO − 3 deposition flux to the Arabian Sea surface is determined to be 0.9 mg m −2 d −1 based on the NO − 3 / 210 Pb ratio (43 μg/dpm −1 ) and the measured 210 Pb deposition flux of 20 dpm m −2 d −1 . The atmospheric NO − 3 flux to the mixed layer is insignificant compared to that fixed by primary production in this region and that supplied to the mixed layer from the base of the euphotic zone. The annual mean 210 Pb concentration (25 × 10 −3 dpm m −3 ) and its atmospheric deposition flux (20 dpm m −2 d −1 ) yield an effective deposition velocity of ∼0.9 cm s −1 for 210 Pb aerosols; similar to that used for deriving NO − 3 and NH + 4 deposition fluxes. The seasonal trend for SO 2− 4 concentrations is quite similar to that of NO − 3 , with the non-sea-salt component of SO 2− 4 being generally higher during the winter and the intermonsoon periods. DOI: 10.1034/j.1600-0889.1999.t01-3-00001.x