Turbidity Trends Research Articles

Fuzzy model identification and control system design for coagulation chemical dosing of potable water

A practical feedforward control system with fuzzy feedback trim is presented for controlling the dosing strategy of Changhsing Water Purification Plant of Taipei Water Department (TWD). The feedforward move is based on a regression model from successful dosing data between 2001 and 2004. The expert operators' adjusting actions in meeting the settled water turbidity trend and pH values are adopted to establish the fuzzy feedback control rules. A host of field tests have demonstrated the effectiveness of the proposed control strategy.

Much More Than a Turbidity Goal

This article discusses Phase III of the Partnership for Safe Water Self‐Assessment and how improving communication and commitment to optimization at all levels can help strengthen the weak links in the utility, thereby increasing the likelihood that optimization will be maintained for years to come. Phase III Assessment Parameters are given, along with a discussion of administrative involvement, suggestions for involving operational staff, reviewing monthly turbidity trends, and advice on writing the Phase III report that recommends approaching it as a team effort, using information from all members to compile the final report, and including all limiting factors that have affected, are affecting, or may affect filter plant operation and performance.

Comparison of aerosol and climate variability over Germany and South Africa

AbstractA radiation‐based model is employed to evaluate seasonal, interannual, and spatial variability within monthly averaged turbidity (the total column amount of aerosol) at eight stations in South Africa and 13 stations in Germany. Germany has a strong seasonal turbidity trend of summer maxima and winter minima. In South Africa the seasonal turbidity trend is weaker, but, on average, turbidity peaks in spring and is lowest in autumn and winter. Over the last several decades, turbidity over Germany has decreased significantly at seven stations. The impacts of the El Chichón and Pinatubo volcanic eruptions are evident in the turbidity signatures over Germany. Four stations in South Africa show long‐term trends in turbidity, but there is no consistent trend. Turbidity in Germany appears to be more influenced by aerosols of non‐local origin than in South Africa, where the aerosol load may be of more local origin. Long‐term monthly averages of Ångström's turbidity coefficient β over Germany range between 0.019 and 0.143, and long‐term annual averages range between 0.064 and 0.116. Over South Africa, turbidity is noticeably lower: long‐term monthly averaged β ranges between 0.004 and 0.071, and the long‐term annually averaged β ranges between 0.013 and 0.047. When averaged across all stations in each of the respective countries, turbidity is, on average, between 2.6 and 5.8 times higher in Germany than in South Africa, depending on the time of year.The climate of South Africa is clearly more humid than Germany, although both countries have strong seasonal trends in humidity. South Africa has become more humid over the last several decades. The decrease in turbidity at stations in Germany appears to be due to a reduction in aerosol emissions and/or changes in climatic factors other than humidity. Copyright © 2003 Royal Meteorological Society

Testing long-term trends in turbidity in the Menai Strait, North Wales

This paper examines two data sets, separated by 33 years, for evidence of long-term changes in turbidity in the Menai Strait, North Wales. The rationale for this examination is that there is evidence for a steady deterioration in water clarity in a 27-year time series (1962–1988) of Secchi depth measurements. The data sets compared here were collected in 1963 and 1964, and in 1996, and comprise measurements of sediment concentrations, both organic and inorganic, determined by traditional sampling methods. In addition, the 1996 data set includes daily measurements of total and inorganic suspended sediment load determined by a recording colour sensor, calibrated using the samples from that year. In each of the years 1963, 1964 and 1996, the suspended sediment load is observed to change with an annual cycle; annual mean suspended sediment concentrations are determined by fitting a curve to the data in each year. The result is that there has been a small increase in the suspended sediment load in the Strait between 1963 and 1996, but that this increase is not statistically significant at the 95% confidence level. The concentrations in 1996 are also significantly lower than those predicted by extrapolating the data from the 27-year time series. It is proposed that the turbidity in the Menai Strait is responding to long-term variations in wind forcing: the mean wind strength over the British Isles increased during the period 1960–1990, but then decreased during the 1990s. If this interpretation is correct, it would imply that the trends observed in the Menai Strait would have been widespread in similarly shallow water throughout north-west Europe.

Atmospheric turbidity over Kathmandu valley

The atmosphere of Kathmandu Valley has been investigated by using Sunphotometer and Nephelometer during the pre-monsoon period of 1999. The atmospheric turbidity parameters (extinction coefficient for 500 nm wavelength τ AG and Angstrom coefficient β) are found high in the morning and show decreasing trends from morning to late afternoon on average. Vertical dispersion of pollutants and increasing pollutant flushing rate by increasing wind speed from morning to late afternoon is the cause for this decreasing trend of turbidity over the valley. Being surrounded by high hills all around the valley, horizontal exit of pollutants without vertical dispersion is not possible. The scattering coefficient b scat of aerosols in ground level troposphere is also found high in the morning, which decreases and becomes minimum during afternoon. During late afternoon, b scat again shows a slightly increasing trend. The reason is the increasing vehicular emission during late afternoon rush period. The average values of Angstrom exponent α, β, τ AG and b scat are found to be 0.624±0.023, 0.299±0.009, 0.602±0.022 and 0.353±0.014 km −1, respectively. About 76.8% of the observed values of β lie above 0.2 indicating heavy particulate pollution in the valley. A comparison of observed values of turbidity parameters with other major cities of the world shows that Kathmandu is as polluted as cities like Jakarta, Kansas, Beijing, Vienna, etc.

Seasonal and interannual variability in atmospheric turbidity over South Africa

AbstractAerosols affect climate by attenuating solar radiation and acting as cloud condensation nuclei. Despite their importance in the climate system, our understanding of the time‐space variability of aerosols is fragmentary. Measurements and reliable estimates of atmospheric turbidity—the total column amount of aerosol—are scarce in most countries and this is especially true in the Southern Hemisphere. Very little is known about the seasonal, interannual and spatial variability of aerosols over the southern half of the globe.In this paper, we estimate monthly averaged atmospheric turbidity from surface climate data at eight locations in South Africa, regardless of cloud cover. Findings include new estimates of turbidity trends and variability over South Africa. Seasonal trends are evident at many stations, although there is no consistent trend. Over recent decades, turbidity has generally been stable at six of the eight stations. Our methodology can be applied at any location where the requisite climate data are available and, therefore, holds promise for a more complete, and possibly global, climatology of aerosols. Copyright © 2001 Royal Meteorological Society

Dynamics of Turbidity in the Tweed Estuary

Results are presented of turbidity measurements made in the Tweed Estuary during 14–29 September 1993. The observations covered a spring-neap period of very strong and relatively weak tides, which included strong wave activity at the mouth of the estuary, the aftermath of a strong freshwater inflow event and a minor inflow event which coincided with neap tides. Turbidity levels between the mouth and the limit of saline intrusion during this period were observed to lie in the range 2–30ppm. Temperature–salinity relationships, based on rapid sampling throughout the estuary, often indicated conservative mixing between riverine and coastal waters. Turbidity–salinity relationships throughout the estuary were approximately linear for most of the lower salinity range (<30) although the relationships varied throughout a tidal cycle. At the highest salinities, in the lower 2·5km of estuary, significantly enhanced turbidities occurred during strong, onshore swell-wave conditions. Near-mouth turbidities were very low (<5ppm) at high-water (HW) when the swell-wave height was small (<0·3m). There was no correlation between near-mouth turbidity at HW and tidal range, whereas the correlation between near-mouth turbidity and swell-wave height explained over 90% of the variance in near-mouth turbidity. The temporal trends in freshwater turbidity and freshwater inflow during the fieldwork period were fairly similar. A statistically significant relationship existed between these variables when freshwater turbidity was correlated against inflow 30h earlier. A ‘model’ of turbidity, based on 5 days of inflows and used to hindcast turbidity from 14 days of inflows between 16–29 September, explained over 80% of the variance in freshwater turbidity. Therefore, inflow exerted a significant control on the fluvial turbidity. It appears that very fine-grained particles were responsible for the observed turbidity in the central and upper reaches of the Tweed. During the flood, in the presence of strong wave activity in the coastal zone, larger sediment was rapidly winnowed in the lower reaches, close to the mouth, whereas fine silt particles remained in suspension and reached the limit of saline intrusion.

Trends in background air pollution parameters over India

The Background Air Pollution Monitoring Network (BAPMoN) data from ten stations in the Indian region for the period 1973–1990, has been used to determine the background trends. Falling pH and increasing turbidity trends have been noticed in all but one of the stations. The post 1982 epoch has witnessed fall in annual mean pH at Vishakhapatnam, Allahabad, Pune and Nagpur though the reduction of mean values are not statistically significant at 5% level of confidence. Frequency distributions of the values of turbidity coefficient B(500 nm) for the epochs 1974–1980, 1981–1985 and 1986–1990 are also presented here. The trend of atmospheric burden is seen to be positive upto the second epoch and stable subsequently. The source identification for chemical constituents of rainwater has been examined by carrying out principal component analysis and using BAPMoN rain chemistry data collected in the entire period of 1974–1988.

Atmospheric turbidity parameters in the highly polluted site of Athens basin

Data on atmospheric turbidity coefficients, i.e. Linke factor T L and Angstrom coefficient β, calculated from measurements of broad-band filter at Athens Observatory (NOA), are reported. A linear model fitted to β vs T L for Athens is similar to the models reported for Avignon (France) and Dhahran (Saudi Arabia). The variation in the monthly average values of β and T L is of similar trend to that of Avignon and Dhahran. However, Athens has shown higher values of atmospheric turbidity coefficients than Avignon and similar turbidity levels to Dhahran. Finally, the long-term variation of the monthly mean values of the mid-day turbidity parameters and the broad-band direct and diffuse irradiances under cloudless skies are evaluated for the same period. The turbidity trends in conjunction with the trends of solar radiation components reflect the rapid urbanization and industrialization of the Athens basin.

Determination of turbidity patterns of the Zhujiang estuarine region, South China, using satellite images and a GIS approach

Abstract Landsat MSS images and SPOT HRV data were employed to map the changes in turbidity levels in the Zhujiang estuarine region, South China, during the dry season in the period 1973–1987 at low and high tides. Analysis of turbidity trends and changes in the spatial pattern of high turbidity class was carried out with a GIS software—IDRISI. It was concluded that with the use of OVERLAY and RECLASS functions in the GIS approach a large number of turbidity maps could be easily compared and the turbidity trend determined. The GIS approach further permitted evaluation of the importance of such factors as water depths, mean tidal differences, and water salinity to sedimentation in the study region.

Atmospheric Turbidity at Tucson, Arizona, 1956–83: Variations and Their Causes

Abstract Solar radiation data collected over the last 27 years at the University of Arizona have been analyzed to determine the major causes of time variations in the local turbidity of the atmosphere. The most extreme perturbations have been associated with significant volcanic eruptions, Agung on Bali in 1963 and, especially, El Chichon in Mexico in 1982. There is also evidence for a correlation of turbidity with local climatic factors and local smelter activity, but no detectable long-term upward or downward trend in turbidity has been observed. Routine pyrheliometric measurements were used to calculate monthly Linke turbidity factors for the period from June 1956 to June 1983 and related monthly aerosol values for the period from January 1977 to February 1983.

Long path optical extinction and meteorology in the San Francisco Bay area

Comparison of night-time long path extinction (25 km) across San Francisco Bay and local meteorological measurements at Oakland Airport revealed a dominant role of boundary layer mixing on visibility. Inversion depth and inversion depth multiplied by wind speed were both strongly inversely correlated with night-time atmospheric extinction. Oakland Airport wind speed and humidity showed little correlation with the extinction measurements. Stellar extinction was also found to be sensitive to mixing depth. This is important as visibility and turbidity trend studies rarely include mixing depth measurements. These results indicate the importance of developing instruments to use the same light source for remote sensing of atmospheric constituents, wind and humidity.

Interactions between air pollution and solar radiation

The interaction between air pollutants and solar radiation is discussed in terms of three examples: measurements of the direct solar beam to determine atmospheric turbidity; the role of solar radiation in initiating photochemical smog processes; and urban-rural differences of incident solar energy. Turbidity measurements from several non-urban stations, particularly in the south-central and south-eastern U.S., show a slight increase during the past 10–15 yr, with most of the change occurring during summer. Measurements at certain urban stations indicate a decreasing turbidity trend. Coincident measurements of incident solar radiation at urban and rural sites are presented for St. Louis and Los Angeles. The urban-rural differences of incident total and ultraviolet (UV) solar energy ranged from near zero to more than 50 per cent. The solar depletion was much larger over Los Angeles than St. Louis. The impact of solar radiation on photochemical smog over Los Angeles is shown be discussing the sensitivity of ozone concentrations to variations of UV radiation. The results of a numerical photochemical diffusion model indicate that the seasonal decrease of UV energy from July to November has a substantial effect on ozone levels, especially over the western part of the Los Angeles Basin.

Solar Radiation: Effects of Atmospheric Water Vapor and Volcanic Aerosols

Abstract Atmospheric water vapor attenuates normal incidence solar radiation received on Mauna Loa, Hawaii, by up to 10%. During periods of active fountaining, aerosols from Kilauea Volcano at times obscure global trends in atmospheric turbidity. Corollary measurements such as precipitable water and the aureole are necessary in order to evaluate the effects upon solar radiation of global trends in atmospheric turbidity.

Turbidity Trends at Tucson, Arizona

Variations in atmospheric turbidity at Tucson, Arizona, since 1956 are similar to those at Mauna Loa in Hawaii, especially before January 1970. The turbidity at both locations increased markedly in 1963 after the Bali eruption. Since January 1970, the turbidity has returned to its pre-1963 level at Mauna Loa, but has remained relatively high at Tucson.