Turbidity Coefficient Research Articles

Validation of MODIS retrieval aerosol optical depth and an investigation of aerosol transport over Mohal in north western Indian Himalaya

This study deals with the optical properties of aerosols during 2007 over Mohal (31.9º N, 77.12º E) in north western Indian Himalaya, investigated using ground-based measurements and multi-satellite data. The daily average (mean ± standard deviation) aerosol optical depth (AOD) at 500 nm, Ångström exponent and turbidity coefficient values were 0.2 ± 0.1, 1.1 ± 0.3 and 0.1 ± 0.1, respectively. About 84% of AOD values retrieved from satellites were found to be within an uncertainty limit with a significant correlation coefficient around 0.70. The present study suggests that AOD retrieval using the Moderate Resolution Imaging Spectroradiometer (MODIS) is able to characterize AOD distribution over Mohal. However, to eliminate systematic errors, the existing MODIS algorithm needs to be modified in view of the changing aerosol optical properties, especially during the biomass-burning period. To investigate the influence of aerosol transport, a multi-sensor approach in conjunction with back-trajectory analysis was used. The observed higher values of AOD during dust-loading days with simultaneous study of the space-borne lidar measurements as well as back-trajectory analysis suggest the influx of desert aerosols. Transport of dust aerosols on 12 April, 27 April and 1 June caused a significant reduction in surface-reaching solar irradiance by 43, 40 and 39 W m–2, respectively. Atmospheric forcing during these days increased by 33.8, 33.0 and 33.2 W m–2, which translates into atmospheric heating rates of 0.95, 0.93 and 0.93 K day–1, respectively. This indicates significant climatic implications due to arriving aerosols in north-western Indian Himalaya.

Atmospheric aerosol characteristics retrieved using ground based solar extinction studies at Mohal in the Kullu valley of northwestern Himalayan region, India

Aerosol parameters are measured using a ground-based Multi-wavelength Radiometer (MWR) at Mohal (31.90°N, 77.11°E, 1154 m amsl) in the Kullu valley during clear sky days of a seasonal year. The study shows that the values of spectral aerosol optical depths (AODs) at 500 nm and the Ångstrom turbidity coefficient ‘β’ (a measure of columnar loading in atmosphere) are high (0.41 ± 0.03, 0.27 ± 0.01) in summer, moderate (0.30 ± 0.03, 0.15 ± 0.03) in monsoon, low (0.19 ± 0.02, 0.08 ± 0.01) in winter and lowest (0.18 ± 0.01, 0.07 ± 0.01) in autumn, respectively. The Ångstrom wavelength exponent ‘α’ (indicator of the fraction of accumulation-mode particles to coarse-mode particles) has an opposite trend having lowest value (0.64 ± 0.06) in summer, low (0.99 ± 0.10) in monsoon, moderate (1.20 ± 0.15) in winter and highest value (1.52 ± 0.03) in autumn. The annual mean value of AOD at 500 nm, ‘α’ and ‘β’ are 0.24 ± 0.01, 1.06 ± 0.09 and 0.14 ± 0.01, respectively. The fractional asymmetry factor is more negative in summer due to enhanced tourists’ arrival and also in autumn months due to the month-long International Kullu Dussehra fair. The AOD values given by MWR and satellite-based moderate resolution imaging spectro-radiometer have good correlation of 0.76, 0.92 and 0.97 on diurnal, monthly and seasonal basis, respectively. The AODs at 500 nm as well as ‘β’ are found to be highly correlated, while ‘α’ is found to be strongly anti-correlated with temperature and wind speed suggesting high AODs and turbidity but low concentration of fine particles during hot and windy days. With wind direction, the AOD and ‘β’ are found to be strongly anti-correlated, while ‘α’ is strongly correlated.

Study on Correlation of Angstrom Turbidity Coefficient (β) with Aerosol Optical Depth (τ) over a Period of Two Years (2004-2006) for the Special Mangrove Ecosystem of Sun-darbans

A study on the correlation of the angstrom turbidity coefficient (β) with aerosol optical depth (τ) have been studied on the basis of field measurements carried out at Kaikhali (22.022°N & 88.614°E) lying in the east coast of India inside the Sundarbans. The angstrom turbidity coefficients have been calculated with respect to the filter channels at 340 nm, 500 nm, 870 nm, 936 nm and 1020 nm of a Sunphotometer. Assessment of the possible influx of the fine particulate concentrations to the total aerosol loading in the area have been made with respect to the calculated angstrom turbidity values for the summer and winter seasons over a period of two years from 2004 to 2006. Substantially high angstrom turbidity coefficient values exceeding 0.2 and indicative of a relatively hazy atmosphere for both the summer and winter periods over these two years from 2004-2006 have been observed. Considering the importance of this fragile mangrove ecosystem of the Sundarbans and also the vulnerability of the area to severe impacts of climate changes, this is indeed a thought provoking issue as far as the policy makers of the country are concerned. In fact, the study has confirmed positive correlation of β with τ.

Semi-empirical models for the estimation of clear sky solar global and direct normal irradiances in the tropics

This paper presents semi-empirical models for estimating global and direct normal solar irradiances under clear sky conditions in the tropics. The models are based on a one-year period of clear sky global and direct normal irradiances data collected at three solar radiation monitoring stations in Thailand: Chiang Mai (18.78°N, 98.98°E) located in the North of the country, Nakhon Pathom (13.82°N, 100.04°E) in the Centre and Songkhla (7.20°N, 100.60°E) in the South. The models describe global and direct normal irradiances as functions of the Angstrom turbidity coefficient, the Angstrom wavelength exponent, precipitable water and total column ozone. The data of Angstrom turbidity coefficient, wavelength exponent and precipitable water were obtained from AERONET sunphotometers, and column ozone was retrieved from the OMI/AURA satellite. Model validation was accomplished using data from these three stations for the data periods which were not included in the model formulation. The models were also validated against an independent data set collected at Ubon Ratchathani (15.25°N, 104.87°E) in the Northeast. The global and direct normal irradiances calculated from the models and those obtained from measurements are in good agreement, with the root mean square difference (RMSD) of 7.5% for both global and direct normal irradiances. The performance of the models was also compared with that of other models. The performance of the models compared favorably with that of empirical models. Additionally, the accuracy of irradiances predicted from the proposed model are comparable with that obtained from some rigorous physical models.

The assessment of aerosol optical properties over Mohal in the northwestern Indian Himalayas using satellite and ground-based measurements and an influence of aerosol transport on aerosol radiative forcing

The present study deals with the aerosol optical properties which are assessed during the period 2007 to 2009 over Mohal (31.9oN, 77.12oE) in the northwestern Indian Himalaya, using ground-based measurements and multi-satellite data. The daily average value of aerosol optical depth (AOD) at 500 nm, Angstrom exponent and turbidity coefficient are 0.24 ± 0.08, 1.02 ± 0.34 and 0.13 ± 0.05, respectively. The comparative study of satellite and ground-based measurements reveals that the percentage retrieval for daily AOD at 550 nm over Mohal within the expected accuracy (Δτpλ = ±0.05 ± 0.15τpλ) is around 87%, with a significant correlation coefficient of 0.76. The present study suggests that the retrieval of AOD through satellite data is able to characterise the distribution of AOD over Mohal. However, further efforts are needed in order to eliminate systematic errors in the existing Moderate Resolution Imaging Spectroradiometer (MODIS) algorithm. The transport of desert dust and anthropogenic aerosol during high aerosol loading days caused a significant reduction in surface-reaching solar radiation by 149 and 117%, respectively. This large reduction in surface-reaching solar radiation increased the atmospheric heating rate by 0.93 and 0.72 K day−1, respectively. This study indicates significant climatic implications due to the transport of aerosols in the northwestern Indian Himalaya.

Aerosols optical properties in dynamic atmosphere in the northwestern part of the Indian Himalaya: A comparative study from ground and satellite based observations

The present study deals with the aerosol optical property which carried out during April 2006 to March 2007 over Mohal (31.9°N, 77.12°E) in the northwestern Indian Himalaya. The study was conducted using ground based Multi-wavelength Radiometer (MWR) and Moderate Resolution Imaging Spectroradiometer (MODIS) sensor. The daily average aerosol optical depth (AOD) at 500 nm was found to be (mean ± standard deviation) 0.24 ± 0.10. The afternoon AOD values have been noticed to be higher than the forenoon AOD values. Spectral AOD values exhibited larger day-to-day variation in finer aerosols during the observation period. The daily average value of Ångström exponent ‘α’ and turbidity coefficient ‘β’ obtained was 1.10 ± 0.38 and 0.12 ± 0.08 respectively. Higher value of AOD ~ 0.39 ± 0.06 during summer associated with low α ~ 0.73 ± 0.28 has attributed to the increase in the relative dominance of coarse size particles. In winter α ~ 1.21 ± 0.32 indicating a considerable increase in fine size particles, attributed to the anthropogenic activities. The AOD spectra seem to be more wavelength dependent in winter as compared to summer. Comparison of MWR observation with MODIS observation indicates a good conformity between ground-based and satellite derived AOD. The root mean square deviation (RMSD), mean absolute bias deviation (MABD) and correlation coefficient have been found to be ~ 0.08, ~ 0.06 and ~ 0.77 respectively. These results suggest that the AOD retrieval through satellite can be able to characterize AOD distribution over Mohal. However, further efforts to eliminate systematic errors in the existing MODIS products are needed. During the observation period ~ 30%, ~ 47% and ~ 62% air parcels drawn at 4000, 5500 and 8000 m above ground level respectively reached at Mohal which passed through or originated from The Great Sahara. The maximum AOD at 500 nm occurred on 8 May 2006. This has caused a significant reduction in surface reaching solar irradiance by ~ 59 Wm −2. The back trajectory analysis suggested that the highest AOD during summer is due to high degree of human interference in the form of tourism and dust transport from the country lying in the northwestern part of India.

Variation in atmospheric aerosol properties over a tropical urban region associated with biomass-burning episodes – a study using satellite data and ground-based measurements

The change in aerosol properties and ground-reaching solar irradiance in different spectral bands associated with an intense biomass-burning episode has been examined in the present study. Synchronous ground-based measurements on aerosol optical depth (AOD), erythemal ultraviolet radiation (UVery), solar irradiance and light detecting and ranging (LIDAR) observations of aerosol backscatter were carried out in the urban region of Hyderabad, India. Air-mass back-trajectory analysis has been carried out to infer long-range transport of pollutants over the urban environment of Hyderabad. Ground-measured AOD showed ∼50% increase on 3 March 2009 compared to 2 March 2009, along with ∼13% and ∼31% increases in Angström's parameter (α) and turbidity coefficient (β). UVery and global solar irradiance showed ∼24% and ∼10% reduction, respectively, on a turbid day (3 March 2009) compared to a normal day (2 March 2009). The Aqua Moderate Resolution Imaging Spectroradiometer (MODIS) AOD550 also showed higher values associated with long-range transport of aerosols from biomass burning over the region.

Estimation of monthly values of atmospheric turbidity using measured values of global irradiation and estimated values from CSR and Yang Hybrid models. Study case: Argentina

Abstract For ten sites in Argentina, monthly average Angstrom turbidity coefficient β values were estimated using mean monthly global solar irradiation values measured at these sites from the former Argentinean radiometric network REDSOL. The values of the horizontal direct and diffuse components of the global irradiation were estimated using the Yang Hybrid model (YHM) and, to determine the representativeness of those results, they were compared to values from the SWERA database which uses the CSR model, developed by NREL, to make estimates. An inconsistency in the estimated values of the diffuse component was detected, therefore a new expression for that component was proposed, generating a corrected version of the YHM (CYHM). The turbidity coefficient β is considered an independent variable in the equation that estimates the direct transmittance and the values that forces an exact correlation between the measured monthly average global irradiance values with those estimated with the CYHM are considered representative for each site since the RMSE between the monthly global irradiation values of SWERA and CYHM is 11.7%, this value being very close to that found by the designers of the CSR model (10%) when they tested it with meteorological data from USA. The monthly average value estimates of turbidity coefficient β show expected behavior, with values varying according to the season of the year.

Evaluation of long‐term changes of solar radiation in India

AbstractTemporal and spatial variability in annually averaged global irradiance, diffuse irradiance, and bright sunshine duration over twelve stations of solar radiation network of India Meteorological Department (IMD) were evaluated for the period 1971–2005. Annually averaged all‐sky global irradiance decreased between 0.1% (0.3 Wm−2) and 3.6% (9.0 Wm−2) per decade at the stations. The decrease in sunshine duration was concomitant with the decrease in global solar irradiance. The long‐term trends in diffuse irradiance differed markedly between the twelve stations. Significant increasing trend in diffuse irradiance were found at the four stations under all‐sky conditions, while seven stations showed increasing trend under clear sky conditions. The two most probable causes of long‐term trends in radiation are changes in aerosol loading and cloud cover. Trend analyses of Angstrom's turbidity coefficient measured at three stations of IMD during the last three decades indicate that total column aerosol has increased significantly. Trend analysis of bright sunshine duration suggests long‐term decrease at all the stations. Reduction in bright sunshine hours varied from 0.0 to 0.5 h per decade. There is a strong northwest‐northeast gradient in sunshine duration which contributes to the spatial trends in global and diffuse solar irradiance. This paper examines the trends of global irradiance, diffuse irradiance and sunshine duration over India in all‐sky conditions as well as cloud‐free skies so the effect of cloud cover can be examined. Copyright © 2011 Royal Meteorological Society

Analysis of optical properties of atmospheric aerosols inferred from spectral AODs and Ångström wavelength exponent

Abstract Aerosol measurements over a tropical semi-arid site in Anantapur (14.62°N, 77.65°E, 331 m asl), India, provide the variabilities of aerosol characteristics for the period of January 2007–December 2008. The mean values of aerosol optical depth at 500 nm (AOD500 nm) over 2-year period are found to be 0.37 ± 0.11, 0.39 ± 0.13 and 0.30 ± 0.10 during winter, summer and monsoon seasons, respectively. A rather systematic variation is seen with AOD peaking in the month of March, falling off gradually to the lowest value in June and increasing slowly superposed with some modulations, which show a weak secondary peak in October. The mean and standard values of the Angstrom exponent, α (turbidity coefficient, β), are found to be 1.06 ± 0.33 (0.17 ± 0.05) during winter, 0.97 ± 0.35 (0.22 ± 0.04) during summer and 0.85 ± 0.26 (0.16 ± 0.06) during monsoon. The frequency distribution of α is relatively broad with two modes for dusty (α 1) situations. This frequency distribution of α reveals a great dispersion of a values in all seasons thus denoting variability in the aerosol-size distribution. In this study, spectral AOD and Angstrom exponent data are analyzed to obtain information about the adequacy of the simple use of the Angstrom exponent and its variation for characterizing optical properties of aerosols, and exploring possibilities for a more efficient characterization of them. Using the least-squares fit method, the Angstrom parameter, α, is calculated in the spectral interval 380–850 nm, along with coefficients a1 and a2 of the second-order polynomial fit to the plotted logarithm of AOD versus the logarithm of wavelength. The correlations between the coefficients a1 and a2 with months and α are discussed in the paper.

Characteristics of aerosol optical depth and Ångström parameters over Mohal in the Kullu Valley of Northwest Himalayan Region, India

The measurements using a ground based multi wavelength radiometer (MWR) at Mohal (31°54′N, 77°07′E, 1154 m AMSL) in the Kullu valley of Northwestern Himalayan region show that the spectral aerosol optical depth (AOD) and turbidity coefficient, β, are high in summer, moderate in monsoon season, low in winter and lowest in autumn, while wavelength exponent, α, has an opposite trend. Average annual value of AOD at 500 nm is 0.24±0.01, 0.43±0.02, and 0.28±0.02; that of β is 0.14±0.01, 0.22±0.02, and 0.17±0.03; and that of α is 1.06±0.09, 1.16±0.10, and 0.86±0.13, respectively, for clear, hazy and partially clear sky days. The considerably greater value of β on hazy days indicates more coarse particles in mountain haze. The fractional asymmetry factor (AF) is more negative in summer and autumn months. The AOD and β have significantly positive correlation with temperature and wind speed, suggesting high AODs and turbidity on hot and windy days.

Long‐term trends and variability in measured multi‐spectral aerosol optical depth over a tropical urban station in India

AbstractSun photometer‐derived multi‐spectral aerosol optical depth (AOD) measurements made at Pune (18°32′N, 73°51′E), India, during the period May 1998–December 2007 have been used to examine possible long‐term trends and variability. Long‐term mean AOD in the spectral range 380–1020 nm ranged between 0.593 ± 0.11 and 0.220 ± 0.04 with a coefficient of variation (COV) of 34–49%. Day‐to‐day variations in AOD at all the wavelengths in the range 380–870 nm showed significant long‐term increasing trends; the increasing trend at 380 nm being 45% per decade. AODs are higher at shorter wavelengths in winter (December–February) and at longer wavelengths in the pre‐monsoon months (March–May) which implies that relatively smaller‐sized particles are more in winter and larger sized particles of soil dust origin are more during the pre‐monsoon season. Overall mean value of Angstrom‐size exponent (α) at this urban location is 0.55, and the mean turbidity coefficient (β) is 0.76. Value of α is higher in winter season compared to the pre‐monsoon season. Both α and β show long‐term increasing trends of 25.3% and 8.4% per decade, respectively, which points out that with increasing urbanisation and human activity, more and more smaller‐sized aerosols are being added to the atmosphere over the urban regions. Copyright © 2010 Royal Meteorological Society

Some features of winter aerosol and water vapor characteristics over Agra, a semi-arid location in India

Reported in this article are the results of the analysis of extensive observations of aerosol optical, micro-physical characteristics, and precipitable water content (PWC) that have been carried out using compact, multi-band solar radiometers, over a semi-arid station, Agra (27°10′N, 78°05′E, 169 m AMSL) during winter 2004. The aerosol optical depth (AOD), Angstrom wavelength exponent (α), and PWC show, higher values on hazy- and foggy-days and lower values on clear-days. The turbidity coefficient (β) shows higher values for smaller values of α and vice versa. The aerosol size spectra exhibit bi-modal distribution with abundance of accumulation-mode particles during fog and haze occasions, and relatively coarse-mode particles on clear-days. The above features have been explained with co-located PWC and surface-level meteorological parameters. The NOAA HYSPLIT five-day back trajectories indicate the influence of trans-boundary pollution transport over the experimental station during the study period.

A new algorithm for the retrieval of atmospheric diffuse transmittance in Moderate Resolution Imaging Spectroradiometer (MODIS) atmospheric correction: a study in the Bohai Sea

Based on 183 groups of in situ data measured with a spectroradiometer during 2003–2007 in the Bohai Sea, we calculated the atmospheric direct transmittance T, diffuse transmittance t, Ångström exponent α and turbidity coefficient β of aerosol optical thickness, and aerosol multiple forward scattering factor B a. An empirical formula relating B a with the two Ångström parameters, α and β, is established. The determination coefficient between aerosol multiple forward scattering factors, B a, estimated by using the above empirical formula and those measured by using an instrument is 0.85. Based on the formula, a new algorithm for the retrieval of atmospheric diffuse transmittance in Moderate Resolution Imaging Spectroradiometer (MODIS) atmospheric correction, instead of the MODIS standard algorithm, is proposed. Tests of the algorithms with in situ observations show that the MODIS standard algorithm leads to evident overestimation of diffuse transmittance, while the new algorithm contributes to a notable improvement in accuracy, especially for cases where the value of diffuse transmittance is small. The relative error and rms. error of the new algorithm are merely about a third and a quarter of those obtained by the MODIS standard algorithm, respectively. The new algorithm gives an estimation of t that matches very well with in situ observations in the Bohai Sea. The proposed algorithm can be utilized in MODIS atmospheric correction as an alternative algorithm, which may improve the accuracy of MODIS atmospheric correction in the Bohai Sea and other near-shore areas with large aerosol optical thickness.

Performance Comparison of Various Filters Media in Water Treatment (Statistical Study)

In this research, a bench-scale filter is designed and constructed in order to compare the performance of different media namely, sand, crushed marble stone and crushed red brick. The filters are operated under various operating conditions such as filter depth, raw water turbidity, pretreatment, effective size and uniformity coefficient. These filters are operated under conventional and direct filtration modes with different doses of alum. Statistical methods had been used to determine the best media using Duncan multiple range test. The result showed the superiority of crushed red brick media in the removal of turbidity and total bacteria. The results also indicated that filters operated under direct filtration mode show better performance than that operated under conventional filtration mode. The pH of treated water show slight increase for the two modes of filtration.

ALTERED STATE OF THE ANTIOXIDATIVE DEFENSE SYSTEM (AODS) IN NEUROLEPTIC-NAIVE FIRST EPISODE SCHIZOPHRENIA

This paper presents the long – term observational studies on aerosol optical properties measured at Sri Krishnadevaraya University (SKU) campus (14° 62′ N, 77° 65′ E, 331m asl), Anantapur, in southern India during 2007–2013 using a ground based Multi – Wavelength solar Radiometer (MWR). Seasonal mean values of Aerosol Optical Depth (AOD) for the whole study period were observed to be 0.34 ± 0.03, 0.45 ± 0.04, 0.24 ± 0.04, and 0.31 ± 0.03 during the winter, summer, monsoon and post – monsoon, respectively. Annual mean values of Ångström exponent (α) (turbidity coefficient (β)) varied from 0.68 ± 0.25 (0.18 ± 0.03) to 1.1 ± 0.12 (0.32 ± 0.12) during 2007–2013. However, high values of α in the range of 0.8–1.1 were observed during the winter, while low values in the range 0.3–0.7 were noticed during the monsoon. The frequency distribution of AODs during winter in the range of 0.2–0.4 is about 78%, while summer these were shifted from 0.3 to 0.6 around ∼70%, which indicated the dust strongly affects this region. The accumulated frequencies of Ångström exponent (α) less than 1.0 and greater than 1.0 were about 69% and 31%, respectively, occurred in the summer months indicates the dominance of coarse particles. Columnar size distributions, retrieved from the spectral optical depths, in general, show a bimodal log normal distribution in the optically active size range. The seasonal mean effective radius (Reff) was found to be high in monsoon (∼0.61 μm) and low in winter (∼0.38 μm). The highest mean mass loading values are lies between 475 ± 36 to 769 ± 49 mg m−2 during the summer, whereas the lowest value in the range 204 ± 19 to 278 ± 23 mg m−2 during the monsoon. The difference between α and curvature effect have been studied as a function of AOD on seasonal basis. Finally, to understand the contribution of long range transported aerosols, we have investigated this analysis making use of back trajectories obtained from the HYSPLIT model for different seasons.

Performance Comparison of Various Filters Media in

In this research, a bench-scale filter is designed and constructed in order to compare the performance of different media namely, sand, crushed marble stone and crushed red brick. The filters are operated under various operating conditions such as filter depth, raw water turbidity, pretreatment, effective size and uniformity coefficient. These filters are operated under conventional and direct filtration modes with different doses of alum. Statistical methods had been used to determine the best media using Duncan multiple range test. The result showed the superiority of crushed red brick media in the removal of turbidity and total bacteria. The results also indicated that filters operated under direct filtration mode show better performance than that operated under conventional filtration mode. The pH of treated water show slight increase for the two modes of filtration.

Inhibition of hatchability of African catfish (Clarias gariepinus) eggs on-farm by rainfall, sunshine and water stagnation

To diagnose the impact of rainfall and temperature range on hatchability of Clarias gariepinus eggs incubated in hapas and in outdoor basins, some incubating eggs were protected against the physical impact of raindrops, some were subjected to various turbidity levels, some were protected from direct sunrays and others were incubated at various densities (number of eggs/litre of water) in flowing Vs stagnant water. Data analyses showed that, unaffected by impact of raindrops (P greater than 0.05), hatchability was inversely proportional to both turbidity (coefficient = -0.971), exposure to sunshine (P less than 0.007) and incubation density (coefficient = -0.973). Measures to ensure that on-farm incubation systems are free from turbidity, wide temperature fluctuations and anoxia, were thus highlighted as prerequired for successful incubation of Clarias gariepinus eggs.

A study on the variations of optical and physical properties of aerosols over a tropical semi-arid station during grassland fire

The present paper records the results of a case study on the impact of an extensive grassland fire on the physical and optical properties of aerosols at a semi-arid station in southern India for the first time from ground based measurements using a MICROTOPS-II sunphotometer, an aethalometer and a quartz crystal microbalance impactor (QCM). Observations revealed a substantial increase in aerosol optical depth (AOD) at all wavelengths during burning days compared to normal days. High AOD values observed at shorter wavelengths suggest the dominance of accumulation mode particle loading over the study area. Daily mean aerosol size spectra shows, most of the time, power-law distribution. To characterize AOD, the Angstrom parameters (i.e., alpha and beta) were used. Wavelength exponent (1.38) and turbidity coefficient (0.21) are high during burning days compared to normal days, thereby suggesting an increase in accumulation mode particle loading. Aerosol size distribution suggested dominance of accumulation mode particle loading during burning days compared to normal days. A significant positive correlation was observed between AOD at 500 mn and water vapour and negative correlation between AOD at 500 nm and wind speed for burning and non-burning days. Diurnal variations of black carbon (BC) aerosol mass concentrations increased by a factor of similar to 2 in the morning and afternoon hours during burning period compared to normal days.

Analysis of atmospheric turbidity levels at Taichung Harbor near the Taiwan Strait

In this study, two universal turbidity parameters, the Angstrom turbidity coefficient and Linke turbidity factor, are applied to study the atmospheric turbidity characteristics of Taichung Harbor. Meteorological parameter values were measured during 2004 and 2005 at the Wuchi weather station of the Taiwan Central Weather Bureau, near the Taiwan Strait. Results based on the Angstrom turbidity models ( β Lou, β Pin, and β Vis) indicated that annual mean values of the Angstrom turbidity coefficients were 0.174, 0.21 and 0.201, respectively. Four sets of Linke turbidity factors ( T Lin, T Lou, T Pin and T Vis) were calculated using the original Linke method and the Dogniaux method, incorporating the computed Angstrom turbidity coefficients ( β Lou, β Pin and β Vis); the resultant values were 4.30, 6.40, 7.10 and 6.95, respectively. The monthly average values, frequency of occurrence, and cumulative frequency distributions were calculated using different models to describe the clear-sky atmospheric conditions at Taichung Harbor. The frequency results show that for over 50% of the dataset, three sets of Angstrom turbidity coefficients fell between 0.15 and 0.18, and four sets of Linke turbidity factors ( T Lin, T Lou, T Pin and T Vis) fell between 4.0 and 6.5. Thus, for 50% of cloudless days, the sky can be between turbid and clear over Taichung Harbor. Furthermore, the results reveal that for 30% of the dataset, three Angstrom sets of turbidity coefficients ( β Lou, β Pin, and β Vis) exceed 0.2 and four sets of Linke turbidity factors ( T Lin, T Lou, T Pin and T Vis) exceed 5.0. This indicates that 30% of cloudless sky conditions can be considered turbid to very turbid.