Concentrations of nitrogen dioxide throughout the state of Bahrain

A comprehensive field study of atmospheric NO2 was conducted throughout the state of Bahrain, using passive diffusion tube samplers. A total of 319 tubes were used, and all sites were chosen to include residential, heavy and low traffic roads, industrial, airport and commercial areas. The results of the survey revealed marked spatial variations in NO2 concentrations. The weekly mean NO2 values varied from 76 microg m(-3) in the north-eastern part of Bahrain island to 13 microg m(-3) in the south-east of Muharaq island. Generally, NO2 values decreased from the north to the south, where traffic volume and density also decreased. In addition, the results indicated that high traffic areas revealed higher NO2 levels compared with airport and industrial areas. The highest NO2 concentrations were measured in roads characterized by being narrow and confined, with many traffic lights and roundabouts, indicating the influence of road geometry on NO2 levels. The results provide valuable baseline information for future investigators, especially since the study was conducted at the start of the Gulf War, which was accompanied by substantial emissions of NO2 from jet fighters and burning of about 600 oil fields.     

Simultaneous removal of nitrogen oxide/nitrogen dioxide/sulfur dioxide from gas streams by combined plasma scrubbing technology

Oxides of nitrogen (NOx) [nitrogen oxide (NO) + nitrogen dioxide (NO2)] and sulfur dioxide (SO2) are removed individually in traditional air pollution control technologies. This study proposes a combined plasma scrubbing (CPS) system for simultaneous removal of SO2 and NOx. CPS consists of a dielectric barrier discharge (DBD) and wet scrubbing in series. DBD is used to generate nonthermal plasmas for converting NO to NO2. The water-soluble NO2 then can be removed by wet scrubbing accompanied with SO2 removal. In this work, CPS was tested with simulated exhausts in the laboratory and with diesel-generator exhausts in the field. Experimental results indicate that DBD is very efficient in converting NO to NO2. More than 90% removal of NO, NOx, and SO2 can be simultaneously achieved with CPS. Both sodium sulfide (Na2S) and sodium sulfite (Na2SO3) scrubbing solutions are good for NO2 and SO2 absorption. Energy efficiencies for NOx and SO2 removal are 17 and 18 g/kWh, respectively. The technical feasibility of CPS for simultaneous removal of NO, NO2, and SO2 from gas streams is successfully demonstrated in this study. However, production of carbon monoxide as a side-product (approximately 100 ppm) is found and should be considered.     

Effects of sulphur dioxide and nitrogen dioxide, singly and in mixture, on the macroscopic growth of three birch clones

An investigation of some aspects of the effects of low concentrations of the gases, sulphur dioxide and nitrogen dioxide, singly and in mixture, was made on the growth of three birch clones, two of Betula pendula Roth. (silver birch) and one of Betula pubescens Ehr. (downy birch). Comparative measurements of the growth form and dry mass increment were made over one year in glasshouses supplied with charcoal-filtered ambient air, and SO(2) and NO(2), singly or in mixture, at mean concentrations of 62 ppb (nl litre (-1)) of one or both gases. The main effects were found in those plants that were fumigated with SO(2) singly, and SO(2) and NO(2) together. Both treatments induced premature leaf loss and reduction in mass, especially of roots, the effects increasing over time. The heights and initial leaf areas were maintained, apparently at the expense of other parameters. NO(2), if present singly, had little or no effect, but it tended to enhance the damaging effect of SO(2) when the two were applied together. The different clones showed different degrees of response to the pollutants, but these differences became less marked during the second season of fumigation. The effects found are discussed in relation to the annual growth of trees, particularly birch.     

Effects of sulfur dioxide and nitric oxide on mercury oxidation and reduction under homogeneous conditions

This paper is particularly related to elemental mercury (Hg0) oxidation and divalent mercury (Hg2+) reduction under simulated flue gas conditions in the presence of nitric oxide (NO) and sulfur dioxide (SO2). As a powerful oxidant and chlorinating reagent, Cl2 has the potential for Hg oxidation. However, the detailed mechanism for the interactions, especially among chlorine (Cl)-containing species, SO2, NO, as well as H2O, remains ambiguous. Research described in this paper therefore focused on the impacts of SO2 and NO on Hg0 oxidation and Hg2+ reduction with the intent of unraveling unrecognized interactions among Cl species, SO2, and NO most importantly in the presence of H2O. The experimental results demonstrated that SO2 and NO had pronounced inhibitory effects on Hg0 oxidation at high temperatures when H2O was also present in the gas blend. Such a demonstration was further confirmed by the reduction of Hg2+ back into its elemental form. Data revealed that SO2 and NO were capable of promoting homogeneous reduction of Hg2+ to Hg0 with H2O being present. However, the above inhibition or promotion disappeared under homogeneous conditions when H2O was removed from the gas blend.     

Source identification and trends in concentrations of gaseous and fine particulate principal species in Seoul, South Korea

Ambient measurements were made using two sets of annular denuder system during the four seasons (April 2001 to February 2002) and were then compared with the results during the period of 1996-1997 to estimate the trends and seasonal variations in concentrations of gaseous and fine particulate matter (PM2.5) principal species. Annual averages of gaseous HNO3 and NH3 increased by 11% and 6%, respectively, compared with those of the previous study, whereas HONO and SO2 decreased by 11% and 136%, respectively. The PM2.5 concentration decreased by -17%, 35% for SO4(2-), and 29% for NH4+, whereas NO3- increased by 21%. Organic carbon (OC) and elemental carbon (EC) were 12.8 and 5.98 microg/m(-3), accounting for -26 and 12% of PM2.5 concentration, respectively. The species studied accounted for 84% of PM2.5 concentration, ranging from 76% in winter to 97% in summer. Potential source contribution function (PSCF) analysis was used to identify possible source areas affecting air pollution levels at a receptor site in Seoul. High possible source areas in concentrations of PM2.5, NO3-, SO4(2-), NH4+, and K+ were coastal cities of Liaoning province (possibly emissions from oil-fired boilers on ocean liners and fishing vessels and industrial emissions), inland areas of Heibei/Shandong provinces (the highest density areas of agricultural production and population) in China, and typical port cities (Mokpo, Yeosu, and Busan) of South Korea. In the PSCF map for OC, high possible source areas were also coastal cities of Liaoning province and inland areas of Heibei/Shandong provinces in China. In contrast, high possible source areas of EC were highlighted in the south of the Yellow Sea, indicating possible emissions from oil-fired boilers on large ships between South Korea and Southeast Asia. In summary, the PSCF results may suggest that air pollution levels in Seoul are affected considerably by long-range transport from external areas, such as the coastal zone in China and other cities in South Korea, as well as Seoul itself.     

Measurements of personal exposure to nitrogen dioxide in four Mexican cities in 1996

Nitrogen dioxide is a ubiquitous pollutant in urban areas. Indoor NO2 concentrations are influenced by penetration of outdoor concentrations and by indoor sources. The objectives of this study were to evaluate personal exposure to NO2, taking into account human time-activity patterns in four Mexican cities. Passive filter badges were used for indoor, outdoor, and personal NO2 measurements over 48 hr and indoor workplace measurements over 16 hr. Volunteers completed a questionnaire on exposure factors and a time-activity diary during the sample period. An unpaired t test, an analysis of variance (ANOVA), and a linear regression were performed to compare differences among cities and mean personal NO2 concentrations involving housing characteristics, as well as to determine which variables predicted the personal NO2 concentration. Sampling periods were in April, May, and June 1996 in Mexico City, Guadalajara, Cuernavaca, and Monterrey. All 122 volunteers in the study were working adults, with a mean age of 34 (SD +/- 7.38); 64% were female, and the majority worked in public offices and universities. The highest NO2 concentrations were found in Mexico City (36 ppb for outdoor, 57 ppb for indoor, and 39 ppb for personal concentration) and the lowest in Monterrey (19 ppb for outdoor, 24 ppb for indoor, and 24 ppb for personal concentration). Significant differences in NO2 concentrations were found among the cities in different microenvironments. During the sampling period, volunteers spent 85% of their time indoors. The highest personal NO2 concentration was found when volunteers kept their windows closed (p = 0.03). In the regression model adjusted by city and gender, the best predictors of personal NO2 concentration were outdoor levels and time spent outdoors (R2 = 0.68). These findings suggest that outdoor NO2 concentrations were an important influence on the personal exposure to NO2, due to the specific characteristics and personal behavior of the people in these Mexican cities.     

Nitrate reductase activity of needles of Norway spruce fumigated with different mixtures of ozone, sulfur dioxide, and nitrogen dioxide

Four-year-old spruce clones (Picea abies (L.) Karst.) cultivated in sand and provided with a complete nutrient solution, or a solution deficient in magnesium and calcium, were exposed to the pollutant mixtures SO(2)/NO(2), O(3)/NO(2), and O(3)/SO(2)/NO(2), at realistic concentrations for 32 weeks. Fumigation caused a slight increase of total N contents in current year needles, whereas in one-year-old needles N concentrations did not change. The response of nitrate reductase activity to pollutant stress depended on needle age and nutrient supply, respectively. In one-year-old needles fumigation resulted in a significant inhibition of enzyme activity, particularly in Mg and Ca deficient trees. The combination of all three components proved to be most effective in causing a decrease by 60% compared to the control. In contrast, nitrate reductase activity was stimulated in current year needles, especially by O(3)/NO(2) and O(3)/SO(2)/NO(2). Changes in the activity of nitrate and nitrite reductases are considered as a factor contributing to the high phytotoxic potential of pollutant combinations with NO(2).     

Water-soluble ions in nano/ultrafine/fine/coarse particles collected near a busy road and at a rural site

This study investigated water-soluble ions in the sized particles (particularly nano (PM(0.01-0.056))/ultrafine (PM(0.01-0.1))) collected using MOUDI and Nano-MOUDI samplers near a busy road site and at a rural site. The analytical results demonstrate that nano and coarse particles exhibited the highest (16.3%) and lowest (8.37%) nitrate mass ratios, respectively. The mass ratio of NO(3)(-) was higher than that of SO(4)(2-) in all the sized particles at the traffic site. The secondary aerosols all displayed trimodal distributions. The aerosols in ultrafine particles collected at the roadside site exhibited Aitken mode distributions indicating they were of local origin. This finding was not observed for those ultrafine particles collected at the rural site. The mass median diameters (MMDs) of the nano, ultrafine, and fine particles were smaller at the traffic site than at the rural site, possibly related to the contribution of mobile engine emissions.     

Characterization of major chemical components of fine particulate matter in North Carolina

This paper presents measurements of daily sampling of fine particulate matter (PM2.5) and its major chemical components at three urban and one rural locations in North Carolina during 2002. At both urban and rural sites, the major insoluble component of PM2.5 is organic matter, and the major soluble components are sulfate (SO4(2-)), ammonium (NH4(+)), and nitrate (NO3(-)). NH4(+) is neutralized mainly by SO4(2-) rather than by NO3(-), except in winter when SO4(2-) concentration is relatively low, whereas NO3(-) concentration is high. The equivalent ratio of NH4(+) to the sum of SO4(2-) and NO3(-) is < 1, suggesting that SO4(2-) and NO3(-) are not completely neutralized by NH4(+). At both rural and urban sites, SO4(2-) concentration displays a maximum in summer and a minimum in winter, whereas NO3(-) displays an opposite seasonal trend. Mass ratio of NO3(-) to SO4(2-) is consistently < 1 at all sites, suggesting that stationary source emissions may play an important role in PM2.5 formation in those areas. Organic carbon and elemental carbon are well correlated at three urban sites although they are poorly correlated at the agriculture site. Other than the daily samples, hourly samples were measured at one urban site. PM2.5 mass concentrations display a peak in early morning, and a second peak in late afternoon. Back trajectory analysis shows that air masses with lower PM2.5 mass content mainly originate from the marine environment or from a continental environment but with a strong subsidence from the upper troposphere. Air masses with high PM2.5 mass concentrations are largely from continental sources. Our study of fine particulate matter and its chemical composition in North Carolina provides crucial information that may be used to determine the efficacy of the new National Ambient Air Quality Standard (NAAQS) for PM fine. Moreover, the gas-to-particle conversion processes provide improved prediction of long-range transport of pollutants and air quality.     

Rural concentrations of nitrogen dioxide pollution throughout Wales

Monitoring of nitrogen dioxide was carried out at over 50 rural sites in Wales throughout 1986. All sites were chosen so as to be remote from any local sources of NO(2) and the values obtained were deemed to be minimum values for the different regions. Measurements were made using a diffusion tube technique which aimed to give mean concentrations of NO(2) for 2-week exposure periods. The results obtained have been used to generate pollution maps to show mean monthly levels of NO(2) for rural environments throughout Wales. It is apparent that levels of NO(2) are generally higher during the winter months. In addition, annual mean concentrations of the pollutant are greatest in the north-eastern and south-eastern parts of Wales with the lowest levels being found along the western coast. The work marks the completion of the first national survey of nitrogen dioxide pollution in Wales. The data are discussed in terms of the potential threat rural concentrations of NO(2) pose to crops and natural vegetation.     

Increasing concentrations of nitrogen dioxide pollution in rural Wales

Monitoring of nitrogen dioxide pollution was carried out in rural environments throughout Wales during a 1-year survey to quantify any changes in background concentrations and distribution of the pollutant since an earlier survey in 1986. There were 23 sites in the present survey of which 16 had been monitored during the 1986 survey. The remaining 7 sites were based on moorland in mid-Wales within map squares for which critical loads for soil acidification are expected to be exceeded by the year 2005. All sites were chosen so as to be remote from major local sources of NO(2) and the values obtained were deemed to be minimum concentrations for the different regions. Measurements were made using diffusion tubes which aimed to provide mean concentrations of NO(2) for 2-week exposure periods. Concentrations of NO(2) were found to be higher in the winter months for most sites and this is probably related to a greater use of fossil fuels for heating buildings at this time of year. The exception was the high concentrations of NO(2) in May and June for several sites in North Wales, and in July and August for a site on Mount Snowdon. These high summer concentrations in North Wales are thought to be related to increased traffic associated with tourism. It is apparent that there has been a substantial increase in rural concentrations of NO(2) throughout Wales since the earlier survey of 1986. As an average of all 16 sites used in both surveys, there was a 53% increase in the annual mean concentration of NO(2). Also, it is evident that, since 1986, there has been a substantial increase in the area of south-eastern Wales which has a background level in excess of 10 ppb NO(2) and a notable reduction in land area with concentrations below 6 ppb NO(2) as an annual mean concentration. The possible future impact of increasing rural concentrations of NO(2) on Welsh vegetation is discussed with references to estimates of critical levels of NO(2) for adverse effects on plants.     

Bulk deposition in a rural area located around a large coal-fired power station, northeast Spain

This work focuses on bulk deposition in a rural area located around a large coal-fired power station in northeast Spain. Deposition chemistry was characterised by high concentrations of SO(4)(2-), Ca(2+) and NH(4)(+), which were relatively high when compared with other rural areas. Monthly bulk deposition evolution of major ions was the result of two superimposed patterns: one pattern related to the volume of precipitation and the other showed the seasonal influence of the major ionic sources. A major local origin was attributed to bulk deposition of SO(4)(2-), NH(4)(+), and Ca(2+), whereas a relatively higher contribution of an external source was deduced for NO(3)(-), Na(+) and Cl(-). The SO(4)(2-) concentrations showed a significant correlation with the local SO(2) emissions. High levels of Ca(2+) were due to the high alkalinity of soils in the study area, although an external origin was attributed to the frequent air mass intrusions from the Sahara. Sources of NH(4)(+) were related to intensive livestock farming in the area. Total suspended particles exert a marked influence over bulk deposition and neutralisation. Thus, despite the high emissions of SO(2) in the area, neutral pH values have always been attained given that the concentrations of Ca(2+) and NH(4)(+) account for the total neutralisation of NO(3)(-) and SO(4)(2-).     

A short-term diffusive sampler for nitrogen dioxide monitoring in epidemiology.

An automated timed exposure diffusive sampler (TEDS) for sampling nitrogen dioxide (NO2) was developed for use in epidemiological studies. The TEDS sequentially exposes four passive sampling devices (PSD) by microprocessor controlled valves while a pump and air flow guide prevent sampler "starvation." Two TEDS units and two portable, real-time NO2 monitors were tested for accuracy, precision, sensitivity, and linearity of response. The accuracy of the TEDS was within 10 percent of the calibrated NO2 values, and precision was within 10 percent of the means of the measured values. The TEDS sensitivity was 20 to 30 ppb-hour for NO2. Co-location of the TEDS with a chemiluminescent NOx monitor (EPA reference method) showed similar responses to ambient NO2 (R2 = 0.9991). TEDS allows better time resolution than traditional diffusive samplers (i.e., Palmes tube) while sharing their ability to sample a variety of gases.     

Measurements of nitrogen dioxide concentrations at rural sites in the United Kingdom using diffusion tubes

Nitrogen dioxide concentrations have been measured at rural sites in the United Kingdom and have revealed a marked spatial variation. The annual mean NO2 concentration varies from approximately 1 microg Nm-3 in Northern Ireland to approximately 7 microg Nm-3 in East Anglia. Though the temporal resolution of the diffusion tube method is limited by exposure periods of 2-4 weeks, it was possible to detect a marked seasonal variation in NO2 concentration at all sites, with higher values in the winter than in the summer. This is in contrast to the small seasonal variation previously observed at sites in London. Sulphur dioxide concentrations were measured daily using a bubbler method and, if expressed in terms of mass of sulphur and nitrogen, the SO2 and NO2 annual mean concentrations were similar. This is in contrast to an S/N ratio of greater than 3 in total UK emissions of SO2 and NOx. It seems likely that this difference is due to a combination of the different spatial distributions and heights of emissions of SO2 and NOx, the influence of local sources of NOx, and the smaller S/N ratio in Continental European emissions.     

Semicontinuous PM2.5 sulfate and nitrate measurements at an urban and a rural location in New York: PMTACS-NY summer 2001 and 2002 campaigns

Several collocated semicontinuous instruments measuring particulate matter with particle sizes < or =2.5 microm (PM2.5) sulfate (SO4(2-)) and nitrate (NO3-) were intercompared during two intensive field campaigns as part of the PM2.5 Technology Assessment and Characterization Study. The summer 2001 urban campaign in Queens, NY, and the summer 2002 rural campaign in upstate New York (Whiteface Mountain) hosted an operation of an Aerosol Mass Spectrometer, Ambient Particulate Sulfate and Nitrate Monitors, a Continuous Ambient Sulfate Monitor, and a Particle-Into-Liquid Sampler with Ion Chromatographs (PILS-IC). These instruments provided near real-time particulate SO4(2-) and NO3- mass concentration data, allowing the study of particulate SO4(2-)/NO3- diurnal patterns and detection of short-term events. Typical particulate SO4(2-) concentrations were comparable at both sites (ranging from 0 to 20 microg/m3), while ambient urban particulate NO3- concentrations ranged from 0 to 11 microg/m3 and rural NO3- concentration was typically less than 1 microg/m3. Results of the intercomparisons of the semicontinuous measurements are presented, as are results of the comparisons between the semicontinuous and time-integrated filter-based measurements. The comparisons at both sites, in most cases, indicated similar performance characteristics. In addition, charge balance calculations, based on major soluble ionic components of atmospheric aerosol from the PILS-IC and the filter measurements, indicated slightly acidic aerosol at both locations.     

Industrial sources influence air concentrations of hydrogen sulfide and sulfur dioxide in rural areas of western Canada

A survey of monthly average concentrations of sulfur dioxide (SO2) and hydrogen sulfide (H2S) at rural locations in western Canada (provinces of Alberta, British Columbia, and Saskatchewan) was conducted in 2001-2002, as part of an epidemiological study of the effects of oil and gas industry emissions on the health of cattle. Repeated measurements were obtained at some months and locations. We aimed to develop statistical models of the effect of oil and gas infrastructure on air concentrations. The regulatory authorities supplied the information on location of the different oil and gas facilities during the study period and, for Alberta, provided data on H2S content of wells and flaring volumes. Linear mixed effects models were used to relate observed concentrations to proximity and type of oil and gas infrastructure. Low concentrations were recorded; the monthly geometric mean was 0.1-0.2 ppb for H2S, and 0.3-1.3 ppb for SO2. Substantial variability between repeated measurements was observed. The precision of the measurement method was 0.005 ppb for both contaminants. There were seasonal trends in the concentrations, but the spatial variability was greater. This was explained, in part, by proximity to oil/gas/bitumen wells and (for SO2) gas plants. Wells within 2 km of monitoring stations had the greatest impact on measured concentrations. For H2S, 8% of between-location variability was explained by proximity to industrial sources of emissions; for SO2 this proportion was 18%. In Alberta, proximity to sour gas wells and flares was associated with elevated H2S concentrations; however, the estimate of the effect of sour gas wells in the immediate vicinity of monitoring stations was unstable. Our study was unable to control for all possible sources of the contaminants. However, the results suggest that oil and gas extraction activities contribute to air pollution in rural areas of western Canada.     

Analysis of air pollution in two major Korean cities: trends, seasonal variations, daily 1-hour maximum versus other hour-based concentrations, and standard exceedances

This study considers the characteristics of carbon monoxide (CO), nitrogen dioxide (NO(2)), ozone (O(3)) and sulfur dioxide (SO(2)) in two major South Korean cities, including the capital city of Seoul, over a time period of 7-8 years. Changes in the annual mean and percentiles of the daily 1-h maximum and other hour-based concentrations varied according to the compound and city type. Seasonal variations varied according to the compound, yet not with the city type. Both Seoul and Taegu exhibited lower O(3) concentrations in July compared to other summer months. There was a high degree of correlation between the daily 1- and 8-h maximum or daily mean concentrations of all compounds in both cities, with an R(2) of 0.66-0.90 at p<0.0001. It was indicated that for CO and O(3), the 8-h standard was more stringent than the 1-h standard, while for NO(2) and SO(2), the 1-h standard was more stringent than the 24-h standard. The correlation coefficients between the daily 1-h maximum and daily mean concentrations decreased as the maximum concentration values of NO(2), O(3 ), and SO(2) increased in the two cities. For all the target compounds, Seoul recorded a substantially higher frequency of days with concentrations above the relevant 1-, 8-, and 24-h standards compared to Taegu.     

Comparative assessment of ambient air quality in two typical Mediterranean coastal cities in Greece

Air quality data (O3, NO2, NO, CO and SO2) of two Greek coastal cities, Patras and Volos, were analyzed and compared to evaluate: (a) the exceedances of air quality EU threshold values, (b) the diurnal patterns of air pollutants and (c) the "weekend effect" on ozone levels. High ozone levels, close to the thresholds for human health and clearly above the threshold for the protection of plants and ecosystems, were observed in Volos. O3 levels in Volos were higher than those in Patras. NOx levels in Patras were significantly higher than the limits for human health and plants' protection. Both, NOx and SO2 levels were higher in Patras than in Volos. The Patras' harbor high traffic seems to drive the diurnal pattern of SO2 in that city. The examination of the rate of ozone accumulation, during the high O3 period (Apr.-Sep.), revealed the occurrence of two phases, a fast and a slow one, with different durations in each city. We suggest that the occurrence of such two phases' patterns should be considered in relevant ozone studies. In both towns, the O3 levels were higher during weekends in comparison to midweek days, although NO levels were lower. Our results support the hypothesis that the weekend O3 effect is due to a combination of VOC sensitivity of the studied areas and the reduced NOx emissions during weekends. Based on the comparison of the weekend effect in the two cities, we suggest the occurrence of a feedback mechanism between peri-urban natural ecosystems (forests) and the polluting anthropogenic ones (cities).     

Simultaneous removal of NO and SO2 by high-temperature fluidized zero-valent iron processes

A new approach to simultaneously remove nitrogen monoxide (NO) and sulfur dioxide (SO2) by zero valent iron (ZVI) was investigated. Three different parameters, temperature, flux, and ZVI dosage, were tested in fluidized ZVI column studies containing 500 ppmv of NO and SO2, respectively. Under the ZVI dosage of 0.5 g at flux of 0.6 L/cm2 x min for temperature 573 K, there is neither NO nor SO2 reduction. For 623 K and 673 K, complete removal for NO and > 90% removal for SO2 were achieved. For temperatures of 723 K and 773 K, 100% removal was achieved for both NO and SO2. The amounts of NO or SO2 reduction (as milligrams of NO or SO2 per gram ZVI) increased as temperature increased, and linearities were observed with both correlation coefficients > 0.97. Compared with NO, SO2 had earlier breakthrough because of a slower diffusion rate and less reactivity but higher mass reduction because of a higher molecular weight for SO2 (64 g/mol for SO2 and 30 g/mol for NO). At same temperature, both NO and SO2 reductions (as milligrams of NO or SO2 per gram of ZVI) were constant regardless of either flux or ZVI dosage variation, but breakthrough time was affected by both flux and ZVI dosage. A parameter weight of ZVI/flux (W/F) was developed to represent these two parameters at the same time to assess the breakthrough time of NO and SO2. Higher breakthrough time was achieved for higher W/F value. Moreover, interestingly, longer breakthrough time and more NO and SO2 mass reduction were achieved for combined NO and SO2 than individual NO or SO2 treated by ZVI, and both oxidation and reduction reactions occurred instead of a reduction reaction only. Chemical reactions among ZVI/NO, ZVI/ SO2, and ZVI/NO/SO2 were also proposed and verified by X-ray diffraction analyses.     

Summer-time distribution of air pollutants in Sequoia National Park, California

Concentrations of air pollutants were monitored during the May November 1999 period on a network of forested sites in Sequoia National Park, California. Measurements were conducted with: (1) active monitors for nitric oxide (NO), nitrogen dioxide (NO2) and ozone (O3); (2) honeycomb denuder/filter pack systems for nitric acid vapor (HNO3), nitrous acid vapor (HNO2), ammonia (NH3), sulfur dioxide (SO2), particulate nitrate (NO3-), ammonium (NH4+), and sulfate (SO4(2-)); and (3) passive samplers for O3, HNO3 and NO2. Elevated concentrations of O3 (seasonal means 41-71 ppb), HNO3 (seasonal means 0.4-2.9 microg/m3), NH3 (seasonal means 1.6-4.5 microg/m3), NO3 (1.1-2.0 microg/m3) and NH4+ (1.0-1.9 microg/m3) were determined. Concentrations of other pollutants were low. With increasing elevation and distance from the pollution source area of O3, NH3 and HNO3 concentrations decreased. Ammonia and NH4+ were dominant N pollutants indicating strong influence of agricultural emissions on forests and other ecosystems of the Sequoia National Park.