Evaluation of a reactive plume model with power plant plume data—application to the sensitivity analysis of sulfate and nitrate formation

A reactive plume model that treats secondary aerosol formation is used to investigate the major physical and chemical processes that affect the rate of sulfate and nitrate aerosol formation in power plant plumes. The reactive plume model is evaluated with experimental data collected in three power plant plumes, and model performance is shown to be quite satisfactory. One of these case studies is used to perform singleparameter and multi-parameter analyses of the sensitivity of sulfate and nitrate aerosol concentrations to various meteorological, air quality and chemical kinetic parameters. The results suggest that sulfate aerosol concentrations are most sensitive to relative humidity and temperature at high relative humidity, whereas nitrate aerosol concentrations are most sensitive to temperature, particularly at low relative humidity. The importance of the NO_x/reactive hydrocarbon chemistry to sulfate and nitrate aerosol formation is examined.     

A modeling study of SOx-NOx-Hydrocarbon plumes and their transport to the background troposphere

A model which emulates the behavior of urban-industrial plumes has been developed and used to analyze the chemical reaction processes occurring as a polluted air mass is transported from an urban area. A 73-step reaction mechanism describing hydrocarbon/NO_xSO_x chemistry was used, with photolytic rate constants depending on the latitude, time of day and time of year. The model includes the physical processes of plume dilution, entrainment and dry deposition, and is simulated under a diurnally varying mixing layer or neutral atmospheric stability conditions.Simulation results are compared with reported field measurements for plumes from St. Louis, Milwaukee, and a power plant plume entrained in the Milwaukee urban plume. The agreement with field concentrations and SO₂ transformation rate data is good, the latter ranging from 1 to 12 % h⁻¹. The study was extended to hypothetical plumes for parametric analysis. In every case considered, the classic O₃ peak occurred at about 3:30 p.m., essentially independent of initial concentrations and plume departure time. The analysis also indicated that substantial SO₂ oxidation via homogeneous gas phase chemistry can occur at night-time, the prerequisite being a high HG/NO_x ratio.     

The APCA Exhibition

On June 5 and 6 of 1980, two parallel plume oxidation studies were carried out in the vicinity of the Tennessee Valley Authority's Colbert Steam Plant. One study was performed in a smog chamber into which stack gases were injected and mixed with ambient air. The other study included direct airborne sampling of the power plant plume. Atmospheric oxidation rates for the conversion of SO₂ to SO₄ ^2- and the removal rates of NO _x (which is presumably the rate of NO₃ ^- formation) were estimated for both studies. The SO₂ to SO₄ ^2- rate coefficients were found to be 0.022 ± 0.009 h^-1 for both chamber experiments and the first airborne sampling day. For the second day, a rate constant of 0.041 ± 0.052 h^-1 was estimated from the aircraft data. The large deviation in this value is explained by the fact that the plume from the power plant combined and reacted with the urban plume from the city of Florence, AL. The formation of a very large "O3 bulge" on this day is also attributed to the mixed plumes. The first order rate coefficients for NO _x removal were estimated to be 0.27 ± 0.14 h^-1 for both chamber experiments and the first airborne sampling day. A NO _x removal rate could not be determined for the second airborne sampling day.     

Rates of Conversion of Sulfur Dioxide to Sulfate in a Scrubbed Power Plant Plume

ABSTRACT

The rate of conversion of SO₂ to SO₄ ^2- was re-estimated from measurements made in the plume of the Cumberland power plant, located on the Cumberland River in north-central Tennessee, after installation of flue gas desulfurization (FGD) scrubbers for SO₂ removal in 1994. The ratio of SO₂ to NO_y emissions into the plume has been reduced to ~0.1, compared with a prescrubber value of ~2. To determine whether the SO₂ emissions reduction has correspondingly reduced plume-generated particulate SO₄ ^2- production, we have compared the rates of conversion before and after scrubber installation. The prescrubber estimates were developed from measurements made during the Tennessee Plume Study conducted in the late 1970s. The post-scrubber estimates are based upon two series of research flights in the summers of 1998 and 1999. During two of these flights, the Cumberland plume did not mix with adjacent power plant plumes, enabling rate constants for conversion to be estimated from samples taken in the plume at three downwind distances. Dry deposition losses and the fact the fact that SO₂ is no longer in large excess compared with SO₄ ^2- have been taken into account, and an upper limit for the conversion rate constant was re-estimated based on plume excess aerosol volume. The estimated upper limit values are 0.069 hr^-1 and 0.034 hr^-1 for the 1998 and 1999 data, respectively. The 1999 rate is comparable with earlier values for nonscrubbed plumes, and although the 1998 upper limit value is higher than expected, these estimates do not provide strong evidence for deviation from a linear relationship between SO₂ emissions and SO₄ ^2- formation.     

Field studies of a power plant plume in the arid southwestern United States

A study is presented of the physics and chemistry relevant to the visual impact of the plume from an electric power generating plant located in the Mojave Desert. The amount of light absorption by particles in the plume did not differ significantly from that by particles in the ambient air. While sulfate and nitrate occasionally contributed substantially to the total particle mass in the plume, generally they contributed < 10% to that mass, with the contribution of sulfate substantially greater than that of nitrate. Mean rates of gas-to-particle conversion in the plume were ∼ 0.6% h⁻¹ for sulfate and ∼ 0.08% h⁻¹ for nitrate. Light scattering by the plume was more dependent on the total mass of particles in the sub-μm size range than on sulfate mass alone. At a wavelength of 550 nm, NO₂ absorption frequently contributed about equally with light scattering particles to the optical depth of the plume.     

Oxidation of nitric oxide controlled by turbulent mixing in plumes from oil sands extraction plants

Results are presented of airborne measurements taken in oil sands extraction plant plumes in Fort McMurray, Alberta, Canada. Measurements with fast response monitors at a high sampling rate illustrate the narrow reaction zone in the plume caused by a turbulent diffusion reaction of NO to NO₂ as suggested by theoretical and laboratory studies. The measured conversion rates of NO to NO₂ varied considerably from day to day, from 0.2 to 21.4% min⁻. Analysis of the oxidation rate of NO to NO₂ and of the atmospheric turbulence parameter reveals that, over the distances and time scales within which the plumes are distinguishable from the background, the nitrogen oxides chemistry in the plumes is controlled by the rates at which the plumes mix with the ambient air (containing ozone), rather than by chemical kinetics.     

Measurements of the chemical composition of stratiform clouds

Measurements are reported of the chemical composition of the liquid water and interstitial air in warm (> 0°C), non-precipitating stratus and strato-cumulus clouds at various locations in the eastern United States. Inorganic ionic composition of the cloud water was generally dominated by H⁺, NH₄⁺, NO₃⁻ and SO₄²⁻, similar to the composition of precipitation in this region of the U.S. Concentrations of the corresponding interstitial aerosol species and gaseous HNO₃ were invariably low in comparison to concentrations of the respective ionic species in cloudwater. In contrast, the concentration of NO_x (i.e. NO + NO₂ + organic nitrates) was invariably comparable to or in excess of that of cloudwater nitrate. Sulfur dioxide was found at varying concentrations relative to cloudwater sulfate. In many cases, the SO₂ concentration was quite low (< 0.2 ppb) even in the presence of substantial quantities of cloudwater SO₄²⁻ (> 1 ppb equivalent gas-phase concentration), suggesting large fractional conversion and incorporation into cloudwater. In other cases, in which dilute SO₂ plumes (pso, > 5 ppb) were observed in the cloud interstitial air, the gaseous SO₂ concentration substantially exceeded the cloudwater sulfate concentration.Concentrations of H₂O₂ in cloudwater were found to exhibit strong inverse correlation with interstitial SO₂. Appreciable concentrations of SO₂ in cloud interstitial air and H₂O₂ in cloudwater were only rarely observed to coexist, for the most part only one or the other being present above the limit of detection. These observations are consistent with aqueous-phase oxidation of SO₂ by H₂O₂, as has been inferred previously on the basis of laboratory kinetic studies, and with the hypothesis that depending on relative concentrations, either of these species can be a limiting reagent for in-cloud SO₂ oxidation. The uptake of NO_x as cloudwater nitrate is less complete than the uptake of SO₂ as sulfate, and evidence for the occurrence of similar in-cloud processes causing the conversion of NO or NO₂ to cloudwater nitrate has not been found.     

The evolution of photochemical smog in a power plant plume

The evolution of photochemical smog in a plant plume was investigated with the aid of an instrumented helicopter. Air samples were taken in the plume of the Cumberland Power Plant, located in central Tennessee, during the afternoon of 16 July 1995 as part of the Southern Oxidants Study – Nashville Middle Tennessee Ozone Study. Twelve cross-wind air sampling traverses were made at six distance groups from 35 to 116 km from the source. During the sampling period the winds were from the west–northwest and the plume drifted towards the city of Nashville TN. Ten of the traverses were made upwind of the city, where the power plant plume was isolated, and two traverses downwind of the city when the plumes were possibly mixed. The results revealed that even six hours after the release, excess ozone production was limited to the edges of the plume. Only when the plume was sufficiently dispersed, but still upwind of Nashville, was excess ozone (up to 109 ppbv, 50–60 ppbv above background levels) produced in the center of the plume. The concentrations image of the plume and a Lagrangian particle model suggests that portions of the power plant plume mixed with the urban plume. The mixed urban power plant plume began to regenerate O₃ that peaked at 120 ppbv at a short distance (15–25 km) downwind of Nashville. Ozone productivity (the ratio of excess O₃ to NO_y and NO_z) in the isolated plume was significantly lower compared with that found in the city plume. The production of nitrate, a chain termination product, was significantly higher in the power plant plume compared to the mixed plume, indicating shorter chain length of the photochemical smog chain reaction mechanism.     

Photochemical model performance for PM2.5 sulfate,nitrate, ammonium,and precursor species SO2, HNO3, and NH3 at background monitor locations in the central and eastern United States

Health studies have shown premature death is statistically associated with exposure to particulate matter <2.5 μm in diameter (PM2.5). The United States Environmental Protection Agency requires all States with PM2.5 non-attainment counties or with sources contributing to visibility impairment at Class I areas to submit an emissions control plan. These emission control plans will likely focus on reducing emissions of sulfur oxides and nitrogen oxides, which form two of the largest chemical components of PM2.5 in the eastern United States: ammonium sulfate and ammonium nitrate. Emission control strategies are simulated using three-dimensional Eulerian photochemical transport models.A monitor study was established using one urban (Detroit) and nine rural locations in the central and eastern United States to simultaneously measure PM2.5 sulfate ion (SO₄²⁻), nitrate ion (NO₃⁻), ammonium ion (NH₄⁺), and precursor species sulfur dioxide (SO₂), nitric acid (HNO₃), and ammonia (NH₃). This monitor study provides a unique opportunity to assess how well the modeling system predicts the spatial and temporal variability of important precursor species and co-located PM2.5 ions, which is not well characterized in the central and eastern United States.The modeling system performs well at estimating the PM2.5 species, but does not perform quite as well for the precursor species. Ammonia is under-predicted in the coldest months, nitric acid tends to be over-predicted in the summer months, and sulfur dioxide appears to be systematically over-predicted. Several indicators of PM2.5 ammonium sulfate and ammonium nitrate formation and chemical composition are estimated with the ambient data and photochemical model output. PM2.5 sulfate ion is usually not fully neutralized to ammonium sulfate in ambient measurements and is usually fully neutralized in model estimates. The model and ambient estimates agree that the ammonia study monitors tend to be nitric acid limited for PM2.5 nitrate formation. Regulatory strategies in this part of the country should focus on reductions in NO_X rather than ammonia to control PM2.5 ammonium nitrate.     

Formation of secondary inorganic aerosols by power plant emissions exhausted through cooling towers in Saxony

Background, aim, and scope  The fraction of ambient PM₁₀ that is due to the formation of secondary inorganic particulate sulfate and nitrate from the emissions of two large, brown-coal-fired power stations in Saxony (East Germany) is examined. The power stations are equipped with natural-draft cooling towers. The flue gases are directly piped into the cooling towers, thereby receiving an additionally intensified uplift. The exhausted gas-steam mixture contains the gases CO, CO₂, NO, NO₂, and SO₂, the directly emitted primary particles, and additionally, an excess of ‘free’ sulfate ions in water solution, which, after the desulfurization steps, remain non-neutralized by cations. The precursor gases NO₂ and SO₂ are capable of forming nitric and sulfuric acid by several pathways. The acids can be neutralized by ammonia and generate secondary particulate matter by heterogeneous condensation on preexisting particles. Materials and methods  The simulations are performed by a nested and multi-scale application of the online-coupled model system LM-MUSCAT. The Local Model (LM; recently renamed as COSMO) of the German Weather Service performs the meteorological processes, while the Multi-scale Atmospheric Transport Model (MUSCAT) includes the transport, the gas phase chemistry, as well as the aerosol chemistry (thermodynamic ammonium–sulfate–nitrate–water system). The highest horizontal resolution in the inner region of Saxony is 0.7 km. One summer and one winter episode, each realizing 5 weeks of the year 2002, are simulated twice, with the cooling tower emissions switched on and off, respectively. This procedure serves to identify the direct and indirect influences of the single plumes on the formation and distribution of the secondary inorganic aerosols. Results and conclusions  Surface traces of the individual tower plumes can be located and distinguished, especially in the well-mixed boundary layer in daytime. At night, the plumes are decoupled from the surface. In no case does the resulting contribution of the cooling tower emissions to PM₁₀ significantly exceed 15 μgm⁻³ at the surface. These extreme values are obtained in narrow plumes on intensive summer conditions, whereas different situations with lower turbulence (night, winter) remain below this value. About 90% of the PM₁₀ concentrations in the plumes are secondarily formed sulfate, mainly ammonium sulfate, and about 10% originate from the primarily emitted particles. Under the assumptions made, ammonium nitrate plays a rather marginal role. Recommendations and perspectives  The analyzed results depend on the specific emission data of power plants with flue gas emissions piped through the cooling towers. The emitted fraction of ‘free’ sulfate ions remaining in excess after the desulfurization steps plays an important role at the formation of secondary aerosols and therefore has to be measured carefully.     

Field observations of regional and urban impacts on NO2, ozone,UVB, and nitrate radical production rates in the Phoenix air basin

In the May and June of 1998, field measurements were taken at a site near the Usery Pass Recreation Area, ∼27 miles from the downtown Phoenix area, overlooking Phoenix and Mesa, Arizona. This site was selected to examine the impacts of the Phoenix urban plume on the Usery Pass Recreation Area and surrounding regions. Data were obtained for ultraviolet-B (UVB) radiation, nitrogen dioxide (NO₂), peroxyacetyl nitrate (PAN), ozone (O₃), and carbon monoxide (CO). Nocturnal plumes of NO₂ (in tens of ppb), observed near midnight, were correlated with CO and anti-correlated with O₃. This behavior was consistent with the titration of locally generated NO by boundary layer O₃ to form the nighttime NO₂ plumes that were subsequently transported into the Usery Pass Recreation area. Nitrate radical (NO₃) production rates were calculated to be very high on the edges of these nocturnal plumes. Examination of O₃ and PAN data also indicates that Phoenix is being affected by long-range transport of pollutants from the Los Angeles to San Diego areas. A regional smoke episode was observed in May, accompanied by a decrease in UVB of factor of two and a decrease in O₃ and an increase in methyl chloride. Low level back trajectories and chemical evidence confirm that the smoke event originated in northern Mexico and that the reduced O₃ levels observed at Usery Pass could be partially due to reduced photolysis rates caused by carbonaceous soot aerosols transported in the smoke plume. The results are discussed with regard to potential effects of local pollution transport from the Phoenix air basin as well as an assessment of the contributions from long-range transport of pollutants to the background levels in the Phoenix-Usery Pass area.     

Analysis of the air pollution climate at a central urban background site

Measurements of air pollutants from a background site in central London are analysed. These comprise hourly data for CO, NO, NO₂, O₃, SO₂ and PM₁₀ from 1996 to 2008 and particle number count from 2001 to 2008. The data are analysed in terms of long-term trends, annual, weekly and diurnal cycles, and autocorrelation and cross-correlation functions. CO, NO and NO₂ show a typical traffic-associated pattern with two daily peaks and lesser concentrations at the weekend. Particle number count and PM₁₀ show a similar cycle, but with smaller amplitude. Ozone has an annual cycle with a maximum in May, influenced by the spring maximum in background ozone, but the diurnal and weekly cycles are dominated by losses through reaction with nitric oxide. Particle number count shows a minimum corresponding with maximum air temperatures in August, whereas the CO, NO NO₂ and SO₂ show a minimum in June/July. There is a lower particle count to NO_x ratio at the background site compared to a central London kerbside site (Marylebone Road) and a seasonal pattern in particle count to NO_x and PM₁₀ ratios consistent with loss of nanoparticles by evaporation during atmospheric transport. Sulphur dioxide peaks in the morning in summer, but at midday in winter consistent with emissions from elevated sources mixing down from aloft as the diurnal mixed layer deepens. Implications for epidemiological studies of air quality and health are discussed. Sulphur dioxide, carbon monoxide, nitric oxide and nitrogen dioxide show clear downward trends over the measurement period, PM₁₀ declines initially before levels stabilised, and ozone concentrations increased.     

Modeling of Potential Power Plant Plume Impacts on Dallas-Fort Worth Visibility

ABSTRACT

During wintertime, haze episodes occur in the Dallas-Ft. Worth (DFW) urban area. Such episodes are characterized by substantial light scattering by particles and relatively low absorption, leading to so-called “white haze.” The objective of this work was to assess whether reductions in the emissions of SO₂ from specific coal-fired power plants located over 100 km from DFW could lead to a discernible change in the DFW white haze. To that end, the transport, dispersion, deposition, and chemistry of the plume of a major power plant were simulated using a reactive plume model (ROME). The realism of the plume model simulations was tested by comparing model calculations of plume concentrations with aircraft data of SF₆ tracer concentrations and ozone concentrations. A second-order closure dispersion algorithm was shown to perform better than a first-order closure algorithm and the empirical Pasquill-Gifford-Turner algorithm. For plume impact assessment, three actual scenarios were simulated, two with clear-sky conditions and one with the presence of fog prior to the haze. The largest amount of sulfate formation was obtained for the fog episode. Therefore, a hypothetical scenario was constructed using the meteorological conditions of the fog episode with input data values adjusted to be more conducive to sulfate formation. The results of the simulations suggest that reductions in the power plant emissions lead to less than proportional reductions in sulfate concentrations in DFW for the fog scenario. Calculations of the associated effects on light scattering using Mie theory suggest that reduction in total (plume + ambient) light extinction of less than 13% would be obtained with a 44% reduction in emissions of SO₂ from the modeled power plant.     

Concentration and dry deposition of atmospheric sulfur and nitrogen compounds in Hungary

The level of regional air pollution is regularly monitored at three stations in Hungary. The comparison of regional concentrations of SO₂ and NO₂ to those measured in Budapest shows that urban level concentration of SO₂ is ten times higher than the value for background conditions. The corresponding figure for NO₂ is five. An increase eastwards across the country can be observed for NO₂ and SO₂, while particulate sulphate, nitrate and ammonium have practically identical concentrations. The concentration of gaseous ammonia has a summer maximum, while the annual variation of particulate ammonium suggests a winter maximum. The ratio of the level of nitric acid to aerosol nitrate is higher than unity in summer, while in winter it is less than 1. The dry deposition of sulfur and oxidized nitrogen compounds is comparable to their wet deposition. However, in the case of NH_x (x = 3 or 4) the wet deposition exceeds the dry deposition by an order of magnitude.     

Measurements of SOx,NOx and aerosol species on Bermuda

During August 1982 and January and February 1983, General Motors Research Laboratories operated an air monitoring site on the southwest coast of Bermuda. The data show that the levels of the NO_x and SO_x species reaching Bermuda are determined by the direction of the air flow. The highest levels of sulfate (mean = 4.0 μg m⁻³), nitric acid (126 ppt) and other species are observed when air masses arrive from the northeastern United States while the lowest levels (sulfate = 1.1 μg m⁻³; nitric acid = 41 ppt) occur during air flow from the SE direction. With westerly air flow, increases in many anthropogenic constituents such as particulate sulfate, lead, elemental carbon, sulfur dioxide, nitrogen dioxide, nitric acid and ozone are observed. These species are generally the lowest during SE winds which bring high concentrations of soil- and crustal-related aerosol species. The source of this crustal material appears to be the Sahara Desert. On the average, the levels of anthropogenic constituents are higher in winter because of frequent intrusions of N American air masses. Conversely, the levels of crustal materials are higher in summer when the SE flow is more prevalent.     

Values of NO2:NOx observed in the exhaust plume from a turbine driven compressor installation

Ratios of nitrogen dioxide to total oxides of nitrogen (NO₂: NO_x were obtained for the exhaust plume of a large turbine (10,000 b.h.p.) driven compressor installation situated in southern Alberta. Median values of 0.37, 0.63 and 0.55 were found during mid-summer, early autumn and early winter study periods, respectively. These were not sensitive to downwind travel time, the presence of clouds or stack emission parameters. Ratios for autumn and winter may be explained on the basis of a dynamic equilibrium existing between NO, NO₂ and O₃. The summer ratio was only about one half of that predicted by the simple equilibrium theory.The observed ratios were much larger than the value of 0.15 which seems typical of compressor stations driven by small (1000 b.h.p.) internal combustion engines. They were more comparable to ratios observed in power plant plumes.     

Role of ammonia chemistry and coarse mode aerosols in global climatological inorganic aerosol distributions

We use an inorganic aerosol thermodynamic equilibrium model in a three-dimensional chemical transport model to understand the roles of ammonia chemistry and natural aerosols on the global distribution of aerosols. The thermodynamic equilibrium model partitions gas-phase precursors among modeled aerosol species self-consistently with ambient relative humidity and natural and anthropogenic aerosol emissions during the 1990s.Model simulations show that accounting for aerosol inorganic thermodynamic equilibrium, ammonia chemistry and dust and sea-salt aerosols improve agreement with observed SO₄, NO₃, and NH₄ aerosols especially at North American sites. This study shows that the presence of sea salt, dust aerosol and ammonia chemistry significantly increases sulfate over polluted continental regions. In all regions and seasons, representation of ammonia chemistry is required to obtain reasonable agreement between modeled and observed sulfate and nitrate concentrations. Observed and modeled correlations of sulfate and nitrate with ammonium confirm that the sulfate and nitrate are strongly coupled with ammonium. SO₄ concentrations over East China peak in winter, while North American SO₄ peaks in summer. Seasonal variations of NO₃ and SO₄ are the same in East China. In North America, the seasonal variation is much stronger for NO₃ than SO₄ and peaks in winter.Natural sea salt and dust aerosol significantly alter the regional distributions of other aerosols in three main ways. First, they increase sulfate formation by 10–70% in polluted areas. Second, they increase modeled nitrate over oceans and reduce nitrate over Northern hemisphere continents. Third, they reduce ammonium formation over oceans and increase ammonium over Northern Hemisphere continents. Comparisons of SO₄, NO₃ and NH₄ deposition between pre-industrial, present, and year 2100 scenarios show that the present NO₃ and NH₄ deposition are twice pre-industrial deposition and present SO₄ deposition is almost five times pre-industrial deposition.     

Visibility as related to atmospheric aerosol constituents

A laboratory and field study was performed to assess the contribution to visibility reduction of both light scattering and absorption by air pollutant particles and gases. Gaseous precursors to important visibility-reducing aerosol species were measured. Emphasis was placed on minimizing sampling artifacts for nitrate and sulfate since previous visibility studies were generally subject to substantial errors from these sources. Optical techniques for measuring the particle absorption coefficient and elemental carbon were evaluated. The aerosol species measured were fine and coarse particulate mass, sulfate, nitrate and elemental carbon, plus organic carbon and ammonium ion. The gases measured were nitric acid, NH₃, SO₂, NO₂ and O₃. Sampling was done at San Jose, Riverside and downtown Los Angeles. The light-scattering efficiency of fine particulate nitrate appeared to be higher than that of sulfate, in contrast to the findings of most prior studies. At all sites light scattering by sulfate, nitrate and elemental carbon particles contributed more than half of the light extinction. Light absorption by particles, due almost exclusively to elemental carbon, contributed 10–20% of the extinction.     

Background levels of air and precipitation quality for Europe

This paper is intended to be used by specialists engaged in air and precipitation quality management on regional and continental scales. Major goals are to establish definition, methodology and specific values of background air and precipitation quality for sulfur (S) and nitrogen (N) species to be used in practical applications of air resources management. Major findings are the following:

• 1.(a) 69% of SO₂ and 63 % of NO₂ concentration over Europe originate from continental scale anthropogenic sources,
• 2.(b) 15% of precipitation sulfate and 11% of precipitation nitrate over Europe are contributed by hemispheric background,
• 3.(c) hemispheric background pollution values for Europe were found as 1.25 μg (SO₂-S)m⁻³, 0.80 μg (SO₄²⁻-S)m⁻³, 0.157 mg (SO₄²⁻-S)l⁻¹ and 0.04 mg (NO₃⁻-N)ℓ⁻¹.