SO2 dispersion and monthly evaluation of the industrial source complex short-term (ISCST32) model at Mina Al-Fahal refinery,Sultanate of Oman

Modeling of air pollutant dispersion has been undertaken for emissions of sulfur dioxide (SO(2)) at the Mina Al-Fahal refinery in the Sultanate of Oman. The study was conducted during the period of November 1999 to October 2000. The Industrial Source Complex Short-Term (ISCST32) air pollution model was adopted to predict the ground level concentration of SO(2) in and around the refinery. The modeling results were validated against measured data during the study period. The comparison, based on the monthly average measurements, showed that the model underestimates the observed SO(2) concentrations. However, the predicted ground level concentrations of SO(2) during the months of September, October, November, and June were in better agreement with the observations. The predicted SO(2) values are presented in the form of concentration contours to determine the spatial distribution of SO(2) and to assess the impact on air quality over the survey area. Predicted SO(2) concentrations were found lower than the World Health Organisation (WHO) guideline value of 365 microg/m(3), with the maximum ground level concentrations being found to occur relatively close to the sources of emission. Moreover, concentration contour patterns for the modeled area vary with changes in meteorological conditions. On the basis of this study, the refinery is not likely to cause any significant deterioration in air quality, and predicted concentrations of SO(2) are well below those likely to influence health.     

Effects of Meteorological Parameters on Air Pollutant Concentrations in Elazig,Turkey

In the present study, air pollutant concentrations have been analyzed statistically with meteorological factors in the city of Elazig, which is located in the east Anatolia region of Turkey, for the months of September, October, November, December, January, February, March, and April during the years 2003 and 2004. SPSS code was used for statistical analyses. The relationship between monitored air pollutant concentrations, such as SO₂ and the total suspended particles (TSP) data, and meteorological factors such as wind speed, temperature, relative humidity and pressure was investigated. According to the results of linear and non-linear regression analysis, it was found that there is a moderate and weak level of relation between the air pollutant concentrations and the meteorological factors in Elazig. The correlation between the previous day's SO₂, TSP concentrations and actual concentrations of these pollutants on that day was investigated and the coefficient of determination R was found to be 0.80 and 0.76, respectively. The statistical models of SO₂ and TSP, including all of the meteorological parameters, gave an R of 0.50 and 0.40, respectively. Further, in order to develop this model, the previous day's SO₂ and TSP concentrations were added to the equations. The new model for SO₂ and TSP was improved considerably with R = 0.85 and 0.80, respectively.     

Impact of COVID-19 lockdown on the elemental profile of PM10 present in the ambient aerosol of an educational institute in Kolkata,India

Reduction in air pollution level was prime observation during COVID-19 lockdown globally. Here, the study was conducted to assess the impact of lockdown on the elemental profile of PM₁₀ in ambient aerosol to quantify the elemental variation. To quantify the variation, phase-wise sampling of air pollutants was carried out using the gravimetric method for PM₁₀, while NO₂ and SO₂ were estimated through the chemiluminescence and fluorescent spectrometric method respectively. The elemental constituents of PM₁₀ were carried out using an Inductively Coupled Plasma Optical Emission Spectrometer and their source apportionment was carried out using the Positive Matrix Factorization model. The results showed that PM₁₀, NO₂ and SO₂ reduced by 86.97%, 83.38%, and 88.60% respectively during the lockdown sampling phase. The highest mean elemental concentration reduction was found in Mn (97.47%) during the lockdown. The inter-correlation among the pollutants exhibited a significant association indicating that they originate from the same source. The metals like Mn and Cu were found at a higher concentration during the lockdown phase corresponding to vehicular emissions. The comparative analysis of the elemental profile of PM₁₀ concluded that the lockdown effectuated in reduction of the majority of elements present in an aerosol enveloping metropolitan like Kolkata.     

The impact of urban growth on regional air quality surrounding the Langat River Basin, Malaysia

Studies of air quality were carried out in the towns of Kajang, Nilai and Banting in the Langat River Basin, southern region of Kuala Lumpur to determine the status and trend of air quality. The determination of air quality was based on several parameters such as suspended solids with diameters less than 10???m (PM₁₀) and gaseous pollutants of sulphur dioxide (SO₂), nitrogen dioxide (NO₂), ozone (O₃), and carbon monoxide (CO). Primary concentration data of air pollutants were compiled through fieldwork studies and combined with secondary data obtained from the regular monitoring data as collected by Alam Sekitar Malaysia Sdn. Bhd. (ASMA) on behalf of Malaysian Department of Environment (DOE) at their stations in Kajang and Nilai. Results showed that the average concentrations of PM₁₀, SO₂, NO₂, O_3, and CO at all sampling stations were still below the permissible values recommended by the Malaysian DOE. The level of gaseous pollutants of NO₂, O_3, and CO was recorded at statistically higher levels (p?<?0.05) than values recorded at the control station at Pangsun Recreational Area. These pollutants were suspected to have originated mainly from exhaust systems of motor vehicles. Data for the years 1996 to 2006 as obtained from ASMA showed long-term air quality trends of increasing O₃ and NO₂ concentrations in Kajang whilst concentrations of PM₁₀ recorded at both Kajang and Nilai stations were mostly expected coming from transboundary sources especially biomass burning and the development activities around the study areas.     

Temporal‐spatial variations of air pollutants in Lanzhou,Gansu Province,China, during the spring–summer periods, 2014–2016

In this article, we analyzed the mass concentrations of particulate matter 2.5 micrometers (µm) or less in size (PM_2.5), particulate matter 10 µm or less in size (PM₁₀), sulfur dioxide (SO₂), nitrogen dioxide (NO₂), carbon monoxide (CO), and ozone (O₃) in Lanzhou, the capital of Gansu province, China. We analyzed monitoring data collected from five air quality monitoring stations during the spring–summer period from 2014 to 2016. Our comparison of contaminant concentrations and average diurnal, daily, monthly, and annual concentrations revealed that the average concentrations of PM_2.5 and PM₁₀ amounted to 128.57 and 46.4 micrograms per cubic meters (µg/m³), respectively, exceeding the Chinese National Ambient Air Quality Standard (NAAQS). We used the Pearson correlation coefficient to establish connections between particulate matter and gaseous pollutants. The results show significant differences in the concentration levels of airborne pollutants. The Pearson correlation coefficient between PM_2.5 and PM₁₀ had the highest coefficient of r = 0.842. A correlation between the two particulate matter sizes (PM_2.5 and PM₁₀) and SO₂ was PM_2.5 and SO₂ r = 0.313; PM₁₀ and SO₂ r = 0.279; and CO and the two particulate matter sizes, PM_2.5 and CO r = 0.304; and PM₁₀ and CO r = 0.203. The average monthly ratio for the study months of PM_2.5 to PM₁₀ was 0.361. In addition, we used the hybrid single particle Lagrangian integrated trajectory model for tracking sources and pathways of the air pollutants in Lanzhou.     

Sulfur trioxide formation during oxy-coal combustion

The purpose of this study was to investigate the effects of increased oxygen and carbon dioxide concentration on the formation of sulfur trioxide during oxy-coal combustion in two different types of pilot-scale furnaces: a pulverized-coal and a circulating-fluidized-bed-fired system.For pulverized-coal (PC) testing, concentrations of SO₃ and SO₂ were significantly higher for oxy-fired conditions as compared to air-fired conditions. For a high-sulfur Illinois bituminous coal, SO₃ concentrations were 4–6 times greater on average. When firing a low-sulfur Utah Bituminous coal, SO₃ concentrations were similar for oxy-firing vs. air-firing, and the overall levels were very low compared to the Illinois coal, consistent with differences in the fuel sulfur contents. PC-fired emissions on a normalized mass basis (mass SO₃ per unit energy input) indicated higher SO₃ emissions under air-fired conditions vs. oxy-firing, for both the Illinois and Utah coals.Circulating fluidized bed testing was also carried out using the low-sulfur Utah coal, and SO₃ concentrations were notably higher for oxy-firing vs. air-firing, in contrast to the similar concentration levels observed for PC-firing. When compared on a normalized mass basis, the emissions were similar for both air- and oxy-firing, which is also in contrast to the PC-fired results for this coal.     

Dispersion by wind of CO2 leaking from underground storage: Comparison of analytical solution with simulation

The concentration of CO₂ in air near the ground needs to be predicted to assess environmental and health risks from leaking underground storage. There is an exact solution to the advection–diffusion equation describing trace gases carried by wind when the wind profile is modeled with a power-law dependence on height. The analytical solution is compared with a numerical simulation of the coupled air–ground system with a source of CO₂ underground at the water table. The two methods produce similar results far from the boundaries, but the boundary conditions have a strong effect; the simulation imposes boundary conditions at the edge of a finite domain while the analytic solution imposes them at infinity. The reverse seepage from air to ground is shown in the simulation to be very small, and the large difference between time scales suggests that air and ground can be modeled separately, with gas emissions from the ground model used as inputs to the air model.     

Is Democracy Good for the Environment?

This paper presents empirical evidence to support the existence of a relationship between democracy and one aspect of environmental quality, urban air pollution. The relationship between environmental quality and democracy is explored empirically using a regression analysis of urban air concentrations of three pollutants, sulfur dioxide (SO₂), suspended particulate matter (SPM) and smoke, and two measures of democracy, the Freedom House Index and Polity III. The results suggest a significant and robust negative linear relationship between these pollutant concentrations and democracy level: the higher the level of democracy, the lower the ambient pollution level.     

Impacts on air pollution in urban areas

Environmental management involves controlling various forms of pollution to levels that do not pose a threat to the health of the people and the environment in general. This paper presents a framework to analyze sources of local air pollution in cities. Using an OLS model, an investigation is performed of the relationship among the concentrations of air pollutants [more precisely, concentrations of sulfur dioxide (SO₂), dust, nitric oxide (NO), nitrogen dioxide (NO₂), carbon oxide (CO) and ozone (O₃)], economic activities, and meteorology. Time series analysis leads to a model, that explains a high degree of the variance in the air pollution data. The model is applied to daily time series from three measurement stations in innsbruck, Austria. Estimation results of the model generally fit with the expected relations. Space heating influences SO₂, dust, and NO, while NO₂ levels are primarily affected by traffic. These results also indicate interdependent relations among the pollutants NO, NO₂, O₃, and CO; O₃ levels depend on temperature and sunshine.     

STREAM WATER CHEMISTRY IN WATERSHEDS RECEIVING DIFFERENT ATMOSPHERIC INPUTS OF H+, NH4, NO3−, AND SO42−1

ABSTRACT: Weekly precipitation and stream water samples were collected from small watersheds in Denali National Park, Alaska, the Fraser Experimental Forest, Colorado, Isle Royale National Park, Michigan, and the Calumet watershed on the south shore of Lake Superior, Michigan. The objective was to determine if stream water chemistry at the mouth and upstream stations reflected precipitation chemistry across a range of atmospheric inputs of H⁺, NH₄⁺, NO₃^?_?, and SO₄^2?. Volume-weighted precipitation H⁺, NH₄⁺, NO₃^?_?, and SO₄^2? concentrations varied 4 to 8 fold with concentrations highest at Calumet and lowest in Denali. Stream water chemistry varied among sites, but did not reflect precipitation chemistry. The Denali watershed, Rock Creek, had the lowest precipitation NO₃^?_? and SO₄^2? concentrations, but the highest stream water NO₃^?and SO₄^2? concentrations. Among sites, the ratio of mean monthly upstream NO₃^?_? concentration to precipitation NO₃^?_- concentration declined (p < 0.001, R²= 0.47) as precipitation NO₃^?_? concentration increased. The ratio of mean monthly upstream to precipitation SO₄^2? concentration showed no significant relationship to change in precipitation SO₄^2? concentration. Watersheds showed strong retention of inorganic N (> 90 percent inputs) across inputs ranging from 0.12 to > 6 kg N ha^?1 y^?1. Factors possibly accounting for the weak or non-existent signal between stream water and precipitation ion concentrations include rapid modification of meltwater and precipitation chemistry by soil processes, and the presence of unfrozen soils which permits winter mineralization and nitrification to occur.     

《大气污染防治行动计划》实施环境效果模拟

本研究利用2010年污染源普查数据和MEIC排放清单建立全国大气污染物高时空分辨率排放清单,在此基础上利用2012年环境统计数据对其进行修订建立2012年全国大气污染物高时空分辨率排放清单;结合《大气污染防治行动计划》(以下简称《计划》)研究工作,测算了《计划》实施后在污染源综合治理、落后产能淘汰、能源结构调整方面对SO2、NOx、颗粒物、VOCs的减排量,同时对污染物新增量进行了预测,建立了《计划》实施后全国大气污染物高时空分辨率排放清单;利用CMAQ空气质量模型模拟分析了《计划》实施的空气质量改善效果。结果表明:《计划》实施后,将可以减少641万吨SO2、859万吨NOx、547万吨颗粒物(不含扬尘污染控制)、627万吨VOCs,全国、京津冀、长三角及珠三角区域PM2.5年均浓度将分别比2012年下降22.08%、33.99%、23.98%、24.04%。如果《计划》要求全部落实,可以实现空气质量改善目标。     

TRENDS IN PRECIPITATION AND STREAM CHEMISTRY IN A PRISTINE OLD-GROWTH FOREST WATERSHED,OLYMPIC NATIONAL PARK,WASHINGTON1

ABSTRACT: Human induced long-term changes in precipitation and stream chemistry have been observed in eastern North America and Europe, but few long-term studies have been conducted in coastal western North America. The objectives of this research were to determine: (1) time trends in precipitation and stream chemistry in a pristine old-growth forest watershed, and (2) seasonal patterns in precipitation and stream chemistry. It was conducted in 58 ha West Twin Creek Watershed, Hoh River Valley, Olympic National Park, Washington from 1984 to 1993. Vegetation consists of old-growth forest, with western hemlock, Douglas-fir, western redcedar, Pacific silver fir, and Sitka spruce being the dominant tree species. Annual precipitation varied from 2336 to 4518 mm during the study period with the majority of the rain falling between October and May. Chemistry of precipitation was strongly dominated by oceanic influences with Na and Cl being the dominant ions. The chemistry of the stream was influenced by bedrock weathering and was dominated by Ca, HCO₃, and SO₄ and was not strongly related to precipitation chemistry. The pH of precipitation averaged 5.3 over time and ranged from 4.3 to 7.1, while the stream pH averaged 7.5 and ranged from 5.5 to 9.0. There were few long-term trends in the chemical constituents of bulk precipitation or stream water with the exception of a slight decrease in NO₃ in precipitation and an increase of SO₄ in stream water. A trend of decreasing concentrations of Ca, Mg and Na in precipitation also occurred. There were no significant seasonal patterns in precipitation although the highest SO₄ concentrations usually occurred in late spring and summer perhaps due marine algal activity. Strong seasonal trends occurred in concentrations of HCO₃, SO₄, Ca, Mg, and Na in stream water resulting from weathering and stream flow patterns, with highest ion concentrations occurring just before the onset of the rainy season. Pulses of NO₃ in the stream were observed during fall and early winter resulting from the release of NO₃ which had accumulated in soils or sediments.     

Impact of industrial air pollutants on some biochemical parameters and yield in wheat and mustard plants

The present study was carried out to determine the impacts of SO₂, NO _x , SPM and RSPM, the most common air pollutants, generated mainly due to industries and vehicles, on some biochemical parameters and yield in wheat and mustard plants during 2006. The concentration of SO₂, NO _x , SPM and RSPM was determined at the polluted sites across the seasons, which ranged between 14.29–18.10, 20.81–22.43, 483.65–500.85 and 160.67–171.18 μg m⁻³, respectively. The wheat and mustard plants grown at polluted sites showed significant reduction in chlorophyll ‘a’, chlorophyll ‘b’, total chlorophyll, carotenoid, ascorbic acid, pH, relative water content and yield. The data were further analyzed using a two way ANOVA. It is concluded that the ambient air pollutants have a potential adverse impact on biochemical parameters, which further leads to a reduction in the yield of wheat and mustard crops.     

Evaluation of sulfate resistance of cement mortars containing black rice husk ash

In this paper, black rice husk ashes (BRHAs), which are agrowastes from an electricity generating power plant and a rice mill, were ground and used as a partial cement replacement. The durability of mortars under sulfate attack including expansion and compressive strength loss were investigated. For parametric study, BRHA were used as a Portland cement Type 1 replacement at the levels of 0%, 10%, 30%, and 50% by weight of binder. The water-to-binder ratios were 0.55 and 0.65. For the durability of mortar exposed to sulfate attack, 5% sodium sulfate (Na₂SO₄) and magnesium sulfate (MgSO₄) solutions were used. As a result, when increasing the percentage replacement of BRHA, the expansion and compressive strength loss of mortar decreased. At the replacement levels of 30% and 50% of BRHA, the expansion of the mortars was less than those mixed with sulfate-resistant cement. However, the expansion of the mortars exposed to Na₂SO₄ was more than those exposed to MgSO₄. Increasing the replacement level of BRHA tends to reduce the compressive strength loss of mortars exposed to Na₂SO₄ attack. In contrary, under MgSO₄ attack, when increasing the replacement level of BRHA, the compressive strength loss increases from 0% to 50% in comparison to Portland cement mortar. Results show that ground BRHA can be applied as a pozzolanic material to concrete and also improve resistance to sodium sulfate attack, but it can impair resistance to magnesium sulfate attack.     

Limitations for brine acidification due to SO2 co-injection in geologic carbon sequestration

Co-injection of sulfur dioxide during geologic carbon sequestration can cause enhanced brine acidification. The magnitude and timescale of this acidification will depend, in part, on the reactions that control acid production and on the extent and rate of SO₂ dissolution from the injected CO₂ phase. Here, brine pH changes were predicted for three possible SO₂ reactions: hydrolysis, oxidation, or disproportionation. Also, three different model scenarios were considered, including models that account for diffusion-limited release of SO₂ from the CO₂ phase. In order to predict the most extreme acidification potential, mineral buffering reactions were not modeled. Predictions were compared to the case of CO₂ alone which would cause a brine pH of 4.6 under typical pressure, temperature, and alkalinity conditions in an injection formation. In the unrealistic model scenario of SO₂ phase equilibrium between the CO₂ and brine phases, co-injection of 1% SO₂ is predicted to lead to a pH close to 1 with SO₂ oxidation or disproportionation, and close to 2 with SO₂ hydrolysis. For a scenario in which SO₂ dissolution is diffusion-limited and SO₂ is uniformly distributed in a slowly advecting brine phase, SO₂ oxidation would lead to pH values near 2.5 but not until almost 400 years after injection. In this scenario, SO₂ hydrolysis would lead to pH values only slightly less than those due to CO₂ alone. When SO₂ transport is limited by diffusion in both phases, enhanced brine acidification occurs in a zone extending only 5 m proximal to the CO₂ plume, and the effect is even less if the only possible reaction is SO₂ hydrolysis. In conclusion, the extent to which co-injected SO₂ can impact brine acidity is limited by diffusion-limited dissolution from the CO₂ phase, and may also be limited by the availability of oxidants to produce sulfuric acid.     

Study of individual reactions of the sour compression process for the purification of oxyfuel-derived CO2

Following the feasibility study of sour compression process as a novel purification method of producing NO_x-free, SO₂-free oxyfuel-derived CO₂ using actual fluegas, in this paper, we present the study of the individual reactions taking place in the process in a controlled environment. We have previously showed that an increase of NO/NO₂ concentration in the inlet stream is beneficial for SO₂ removal as NO₂ promotes SO₂ oxidation and the further removal as liquid acid. In this study we show that the reaction SO₂ + NO₂ → SO₃ + NO does not take place significantly in the absence of liquid water at a range of conditions relevant to the sour compression process. When liquid water is present, SO₂ is oxidised by NO₂ regenerating NO with the rate of conversion of SO₂ being dependent on the acid concentration in the liquid. The formation of small liquid droplets where very low levels of pH (?0) can be reached is shown to be of great importance to the SO₂ + NO₂ conversion process.     

Applicability of a continuous-flow system inner-coated with S-doped titania for the photocatalysis of dimethyl sulfide at low concentrations

The present study investigated the photocatalytic activity of an S-doped TiO₂ photocatalyst with regards to dimethyl sulfide degradation under visible-light irradiation, along with its deactivation and reactivation. The dimethyl sulfide conversion was between 85% and 93% for the lowest relative humidity range (10–20%) and close to 100% for the two higher relative humidity ranges (45–55% and 80–90%). The conversion was also close to 100% for the two lowest input concentrations (0.039 and 0.195 ppm), while it was between 91% and 96% at 3.9 ppm and between 85% and 90% at 7.9 ppm. In contrast to the input concentration dependences on conversion, the calculated degradation rates increased as input concentrations increased. The dimethyl sulfide conversion at low concentrations (≤0.39 ppm), which are associated with non-occupational inn occurring. However, catalyst deactivations were observed during the photocatalytic process whdoor air quality issues, was up to nearly 100% for long time periods (at least 603 h), without any significant catalyst deactivatioen higher concentrations (3.9 and 7.8 ppm) were used. The photocatalyst, reactivated by using two types of air (dried and humidified) under visible-light irradiation, did not regain all of its initial activities. Sulfate groups were qualitatively identified as the reaction products on the photocatalyst surface. In addition, gaseous byproducts, quantitatively determined, included dimethyl disulfide, methanol, and SO₂. It is noteworthy that the peak concentration of dimethyl disulfide (0.79 ppm = 790 ppb), generated over the photocatalytic process with the highest dimethyl sulfide input concentration, exceeded the odor threshold value of 0.1–3.6 ppb for dimethyl disulfide.     

Effects of NO,NO<Subscript>2</Subscript>, CO and SO<Subscript>2</Subscript> on NO oxidation over Pt/TiO<Subscript>2</Subscript> for hybrid fast SCR process

The selective catalytic reduction (SCR) rate of NO with N-containing reducing agents can be enhanced considerably by converting part of NO into NO₂. The enhanced reaction rate is more pronounced even at lower temperatures by using an equimolar mixture of NO and NO₂ (fast SCR reaction). The oxidation characteristics of NO over catalyst Pt/TiO₂ have been determined in a fixed bed reactor (8 mm-ID) with different concentrations of oxygen, nitric oxide and nitrogen dioxide in the presence of 8% water. The conversion of NO to NO₂ increases with increasing oxygen (O₂) concentration from 3 to 12%, but it levels off at higher O₂ concentrations. The NO conversion to NO₂ decreases with increasing NO concentration and it also decreases by an addition of NO₂ in the feed stream. Therefore, the oxidation of NO over Pt/TiO₂ catalyst could be auto-inhibited by the reaction product of NO₂. The effects of CO and SO₂ on NO oxidation characteristics have also been determined. In fact, the presence of SO₂ significantly suppresses oxidation of NO but due to the less stability of sulfate on anatase structure in TiO₂, it becomes less significant. On the other hand, the presence of CO increases NO oxidation significantly due to the auto-inhibition effect by CO. Moreover, the effect of SO₂/CO on NO oxidation has also been determined and it was observed that NO oxidation decreases with the increase in SO₂/CO ratio.     

长沙市空气自动站周边区域大气污染物排放源清单

以长沙市空气自动站周边3 km为研究对象,基于统计年鉴和实地调查,获得了该地区2015年储存运输源、废弃物处理源、工艺过程源、化石燃料固定燃烧源、农业源、生物质燃烧源、扬尘源、移动源8个源类的活动水平数据。以大气污染物排放源清单编制技术指南为依据,建立了2015年长沙市空气自动站周边3 km区域NH_3、NO_x、PM_(10)、PM_(2.5)、SO_2、VOCs等6项污染物的源排放清单。结果表明,2015年长沙空气自动站周边3 km内,8类大气污染源排放的NH_3、NO_x、PM_(2.5)、PM_(10)、SO_2、VOCs总量分别为53.65t、4 899.35t、1 846.09t、6 257.75t、989.49t、4 383.31t。NH_3、NO_x、PM_(2.5)、PM_(10)、SO_2、VOCs排放量最大的源分别是农业源、移动源、扬尘源、扬尘源、化石燃料固定燃烧源和移动源,贡献率分别为98.45%、84.24%、60.82%、85.90%、97.33%、49.88%。优化道路交通、减少燃煤、减少建筑工地扬尘排放可促进长沙市空气自动站周边空气质量改善。     

WATERSHED SCALING EFFECT ON BASE FLOW NITRATE,VALLEY AND RIDGE PHYSIOGRAPHIC PROVINCE1

ABSTRACT: A study of stream base flow and NO₃‐N concentration was conducted simultaneously in 51 subwatersheds within the 116‐square‐kilometer watershed of East Mahantango Creek near Klingerstown, Pennsylvania. The study was designed to test whether measurable results of processes and observations within the smaller watersheds were similar to or transferable to a larger scale. Ancillary data on land use were available for the small and large watersheds. Although the source of land‐use data was different for the small and large watersheds, comparisons showed that the differences in the two land‐use data sources were minimal. A land use‐based water‐quality model developed for the small‐scale 7.3‐square‐kilometer watershed for a previous study accurately predicted NO₃‐N concentrations from sampling in the same watershed. The water‐quality model was modified and, using the imagery‐based land use, was found to accurately predict NO₃‐N concentrations in the subwatersheds of the large‐scale 116‐square‐kilometer watershed as well. Because the model accurately predicts NO₃‐N concentrations at small and large scales, it is likely that in second‐order streams and higher, discharge of water and NO₃‐N is dominated by flow from smaller first‐order streams, and the contribution of ground‐water discharge to higher order streams is minimal at the large scale.