Displaying publications 21 - 40 of 51 in total

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  1. Source apportionment of surfactants in marine aerosols at different locations along the Malacca Straits
    Mustaffa NI, Latif MT, Ali MM, Khan MF
    Environ Sci Pollut Res Int, 2014 May;21(10):6590-602.
    PMID: 24532245 DOI: 10.1007/s11356-014-2562-z
    This study aims to determine the source apportionment of surfactants in marine aerosols at two selected stations along the Malacca Straits. The aerosol samples were collected using a high volume sampler equipped with an impactor to separate coarse- and fine-mode aerosols. The concentrations of surfactants, as methylene blue active substance and disulphine blue active substance, were analysed using colorimetric method. Ion chromatography was employed to determine the ionic compositions. Principal component analysis combined with multiple linear regression was used to identify and quantify the sources of atmospheric surfactants. The results showed that the surfactants in tropical coastal environments are actively generated from natural and anthropogenic origins. Sea spray (generated from sea-surface microlayers) was found to be a major contributor to surfactants in both aerosol sizes. Meanwhile, the anthropogenic sources (motor vehicles/biomass burning) were predominant contributors to atmospheric surfactants in fine-mode aerosols.
  2. Characterization and source apportionment of particle number concentration at a semi-urban tropical environment
    Khan MF, Latif MT, Amil N, Juneng L, Mohamad N, Nadzir MS, et al.
    Environ Sci Pollut Res Int, 2015 Sep;22(17):13111-26.
    PMID: 25925145 DOI: 10.1007/s11356-015-4541-4
    Principal component analysis (PCA) and correlation have been used to study the variability of particle mass and particle number concentrations (PNC) in a tropical semi-urban environment. PNC and mass concentration (diameter in the range of 0.25->32.0 μm) have been measured from 1 February to 26 February 2013 using an in situ Grimm aerosol sampler. We found that the 24-h average total suspended particulates (TSP), particulate matter ≤10 μm (PM10), particulate matter ≤2.5 μm (PM2.5) and particulate matter ≤1 μm (PM1) were 14.37 ± 4.43, 14.11 ± 4.39, 12.53 ± 4.13 and 10.53 ± 3.98 μg m(-3), respectively. PNC in the accumulation mode (<500 nm) was the most abundant (at about 99 %). Five principal components (PCs) resulted from the PCA analysis where PC1 (43.8 % variance) predominates with PNC in the fine and sub-microme tre range. PC2, PC3, PC4 and PC5 explain 16.5, 12.4, 6.0 and 5.6 % of the variance to address the coarse, coarser, accumulation and giant fraction of PNC, respectively. Our particle distribution results show good agreement with the moderate resolution imaging spectroradiometer (MODIS) distribution.
  3. Surfactants in atmospheric aerosols and rainwater around lake ecosystem
    Razak IS, Latif MT, Jaafar SA, Khan MF, Mushrifah I
    Environ Sci Pollut Res Int, 2015 Apr;22(8):6024-33.
    PMID: 25382497 DOI: 10.1007/s11356-014-3781-z
    This study was conducted to determine the composition of surfactants in atmospheric aerosols and rainwater in the vicinity of Lake Chini, Malaysia. Samples of atmospheric aerosol and rainwater were collected between March and September 2011 using a high volume air sampler (HVAS) and glass bottles equipped with funnel. Colorimetric analysis was undertaken to determine the concentration of anionic surfactants as methylene blue active substances (MBAS) and cationic surfactants as disulphine blue active substances (DBAS). The water-soluble ionic compositions were determined using inductively coupled plasma mass spectrometry for cations (Na, K, Mg and Ca) and ion chromatography equipped with a conductivity detector for anions (F(-), Cl(-), NO3(-), and SO4(2-)) and the Nessler Method was used to obtain the NH4(+) concentrations. The source apportionment of MBAS and DBAS in atmospheric aerosols was identified using a combination of principal component analysis (PCA) and multiple linear regression (MLR). The results revealed that the concentrations of surfactants in atmospheric aerosols and rainwater were dominated by anionic surfactants as MBAS. The concentration of surfactants as MBAS and DBAS was dominated in fine mode compared to coarse mode aerosols. Using PCA/MLR analysis, two major sources of atmospheric surfactants to Lake Chini were identified as soil dust (75 to 93%) and biomass burning (2 to 22%).
  4. Polycyclic aromatic hydrocarbons in coastal sediments of Southern Terengganu, South China Sea, Malaysia: source assessment using diagnostic ratios and multivariate statistic
    Pang SY, Suratman S, Latif MT, Khan MF, Simoneit BRT, Mohd Tahir N
    Environ Sci Pollut Res Int, 2022 Mar;29(11):15849-15862.
    PMID: 34636003 DOI: 10.1007/s11356-021-16762-6
    Surface sediments along the Southern Terengganu coast (≤7 km from the coast) were analyzed for polycyclic aromatic hydrocarbons (PAHs). The concentrations of 16 USEPA priority polycyclic aromatic hydrocarbons (ΣPAH16) ranged from 2.59 to 155 ng g-1 and their respective alkylated ranged between 8.80 and 24.90 ng g-1. Traces of acephenanthrylene, benzo[c]phenanthrene, thiophenic PAH, and benzonaphthofuran were identified. PAH diagnostic ratios and cross-plots revealed that these sedimentary PAH compounds are derived mainly from pyrogenic sources, primarily from biomass burning and petroleum combustion residues with minor petrogenic input. The high correlations between pyrogenic PAHs to total PAHs (r >0.73, p <0.5), and the Bap/Bep ratio to total PAHs (r = 0.88, p <0.5), suggest that atmospheric deposition and urban runoff are the main deposition pathways. The concentrations of the PAHs in the southern South China Sea fall in the moderate contamination range of 100-1000 ng g-1.
  5. The association between temperature and cause-specific mortality in the Klang Valley, Malaysia
    Yatim ANM, Latif MT, Sofwan NM, Ahamad F, Khan MF, Mahiyuddin WRW, et al.
    Environ Sci Pollut Res Int, 2021 Nov;28(42):60209-60220.
    PMID: 34156627 DOI: 10.1007/s11356-021-14962-8
    This study aims to examine the relationship between daily temperature and mortality in the Klang Valley, Malaysia, over the period 2006-2015. A quasi-Poisson generalized linear model combined with a distributed lag non-linear model (DLNM) was used to estimate the association between the mean temperature and mortality categories (natural n=69,542, cardiovascular n= 15,581, and respiratory disease n=10,119). Particulate matter with an aerodynamic diameter below 10 μm (PM10) and surface ozone (O3) was adjusted as a potential confounding factor. The relative risk (RR) of natural mortality associated with extreme cold temperature (1st percentile of temperature, 25.2 °C) over lags 0-28 days was 1.26 (95% confidence interval (CI): 1.00, 1.60), compared with the minimum mortality temperature (28.2 °C). The relative risk associated with extremely hot temperature (99th percentile of temperature, 30.2 °C) over lags 0-3 days was 1.09 (95% CI: 1.02, 1.17). Heat effects were immediate whereas cold effects were delayed and lasted longer. People with respiratory diseases, the elderly, and women were the most vulnerable groups when it came to the effects of extremely high temperatures. Extreme temperatures did not dramatically change the temperature-mortality risk estimates made before and after adjustments for air pollutant (PM10 and O3) levels.
  6. Ecological risk and source apportionment of heavy metals in surface water and sediments on Saint Martin's Island in the Bay of Bengal
    Sarker KK, Bristy MS, Alam N, Baki MA, Shojib FH, Quraishi SB, et al.
    Environ Sci Pollut Res Int, 2020 Sep;27(25):31827-31840.
    PMID: 32504432 DOI: 10.1007/s11356-020-09384-x
    The study aimed to determine eight hazardous heavy metals in surface water and sediment samples collected from the Naf River, Shah Porir Dwip (estuary), and mostly around Saint Martin's Island in the Bay of Bengal. The results of heavy metals in water samples were ranged as Pb 14.7-313.0, Cd 33.0-70.0, Cr
  7. Health risk estimation of metals bioaccumulated in commercial fish from coastal areas and rivers in Bangladesh
    Bristy MS, Sarker KK, Baki MA, Quraishi SB, Hossain MM, Islam A, et al.
    Environ Toxicol Pharmacol, 2021 Aug;86:103666.
    PMID: 33895355 DOI: 10.1016/j.etap.2021.103666
    Metal contaminations in commercial fish have become a great public health concern worldwide including Bangladesh. The current study was conducted to provide preliminary evidence of nine metals in three commercially significant fish namely Pampus argenteus, Sardinella longiceps and Tenualosa ilisha collected from four coastal stations- Kuakata, Pathorghata, Cox's Bazar, and Pirojpur, and eight stations of five rivers- Padma, Meghna, Jamuna, Katcha, and Nobogonga in Bangladesh. High magnitudes of Pb (0.74-4.59 mg/kg ww), Cd (0.07-0.24 mg/kg ww), and Mn (0.45-2.03 mg/kg ww) were recorded in the sampling stations that exceeded the maximum permissible limits (MPL) proposed by different recognized organizations. Significant mean differences of metal concentrations were observed (p 
  8. Fulltext Optimal control analysis of vector-host model with saturated treatment
    Ullah S, Khan MF, Shah SAA, Farooq M, Khan MA, Mamat MB
    Eur Phys J Plus, 2020;135(10):839.
    PMID: 33101826 DOI: 10.1140/epjp/s13360-020-00855-1
    Vector-host infectious diseases remain a challenging issue and cause millions of deaths each year globally. In such outbreaks, many countries especially developing or underdevelopment faces a situation where the number of infected individuals is getting larger and the medical facilities are limited. In this paper, we construct an epidemic model to explore the transmission dynamics of vector-borne diseases with nonlinear saturated incidence rate and saturated treatment function. This type of incidence rate, as well as the saturated treatment function, is also known as the Holling type II form and describes the effect of delayed treatment. Initially, we formulate a mathematical model and then present the basic analysis of the model including the positivity and boundedness of the solution. The threshold quantity R 0 is presented and the stability analysis of the system is carried out for the model equilibria. The global stability results are shown using the Lyapunov function of Goh-Voltera type. The existence of backward bifurcation is discussed using the central manifold theory. Further, the global sensitivity analysis of the model is carried out using the Latin Hypercube sampling and the partial rank correlation coefficient techniques. Moreover, an optimal control problem is formulated and the necessary optimality conditions are investigated in order to eradicate the disease in a community. Four strategies are presented by choosing different set of controls combination for the disease minimization. Finally, the numerical simulations of each strategy are depicted to demonstrate the importance of suggesting control interventions on the disease dynamics and eradication.
  9. Fulltext Antioxidative role of palm grass rhizome ameliorates anxiety and depression in experimental rodents and computer-aided model
    Hoque MA, Ahmad S, Chakrabarty N, Khan MF, Hafez Kabir MS, Brishti A, et al.
    Heliyon, 2021 Oct;7(10):e08199.
    PMID: 34729435 DOI: 10.1016/j.heliyon.2021.e08199
    Palm grass (Curculigo recurvata) is an ethnomedicinally important herb reported to have significant medicinal values. The present study aimed to evaluate the antidepressant and anxiolytic activities of a methanol extract of C. recurvata rhizome (Me-RCR) through different approaches. The antidepressant and anxiolytic properties of Me-RCR were assessed by using elevated plus maze (EPM), hole-board (HBT), tail suspension (TST), and forced swimming (FST) tests in Swiss Albino mice. The in-depth antioxidative potential of Me-RCR was also evaluated through DPPH radical scavenging activity, ferric-reducing power capacity, total phenolic, flavonoid, flavonol, and antioxidant content analysis. Computational investigations were performed using computer-aided methods for screening the anxiolytic, antidepressant, and antioxidative activities of the selected lead molecules. Treatment with Me-RCR (200 and 400 mg/kg, b.w.) notably increased the number of open arm entries and the time spent in the EPM test. In the HBT, Me-RCR exhibited significant anxiolytic activity at a dose of 200 mg/kg, whereas similar activity was observed at 400 mg/kg in the EPM test. Me-RCR significantly decreased the immobility time in a dose-dependent manner in both TST and FST. The IC50 for DPPH and reducing power capacity assay were found to be 18.56 and 193 μg/mL, respectively. Promising outcomes were noted for the determination of total phenolics, flavonoids, flavonols, and antioxidant capacity. In the case of computer-aided studies, nyasicoside showed promising binding energy for antidepressant and anxiolytic activities, whereas isocurculigine demonstrated promising effects as an antioxidant. Overall, these findings suggest that Me-RCR could be a favourable therapeutic candidate for the treatment of mental and psychiatric disorders, as well as a good source of antioxidants.
  10. Fulltext The long-term assessment of air quality on an island in Malaysia
    Abdul Halim ND, Latif MT, Ahamad F, Dominick D, Chung JX, Juneng L, et al.
    Heliyon, 2018 Dec;4(12):e01054.
    PMID: 30603693 DOI: 10.1016/j.heliyon.2018.e01054
    This study aims to evaluate the air quality on Langkawi Island, a famous tourist destination in Malaysia, using 13 years of data (1999-2011) recorded by the Malaysian Department of Environment. Variations of seven air pollutants (O3, CO, NO, NO2, NOx, SO2 and PM10) and three meteorological factors (temperature, humidity and wind speed) were analysed. Statistical methods used to analyse the data included principal component regression (PCR) and sensitivity analysis. The results showed PM10 was the dominant air pollutant in Langkawi and values ranged between 5.0 μg m-3 and 183.2 μg m-3. The patterns of monthly values showed that the concentrations of measured air pollutants on Langkawi were higher during the south-west monsoon (June-September) due to seasonal biomass burning activities. High CO/NOx ratio values (between 28.3 and 43.6), low SO2/NOx ratio values (between 0.04 and 0.12) and NO/NO2 ratio values exceeding 2.2 indicate the source of air pollutants in this area was motor vehicles. PCR analysis grouped the seven variables into two factor components: the F1 component consisted of SO2, NO and NOx and the F2 component consisted of PM10. The F1 component (R2 = 0.931) indicated a stronger standardized coefficient value for meteorological variables compared to the F2 component (R2 = 0.059). The meteorological variables were statistically significant (p < 0.05) in influencing the distribution of the air pollutants. The status of air quality on the island could be improved through control on motor vehicle emissions as well as collaborative efforts to reduce regional air pollution, especially from biomass burning.
  11. Pharmacological insights on the antidepressant, anxiolytic and aphrodisiac potentials of Aglaonema hookerianum Schott
    Goni O, Khan MF, Rahman MM, Hasan MZ, Kader FB, Sazzad N, et al.
    J Ethnopharmacol, 2021 Mar 25;268:113664.
    PMID: 33278545 DOI: 10.1016/j.jep.2020.113664
    ETHNOPHARMACOLOGICAL RELEVANCE: Aglaonema hookerianum Schott is an ethnomedicinally important plant used to treat a variety of diseases, including sexual and depression-like disorders. However, the scientific basis underlying the aforesaid properties have not been well justified.

    AIM OF THE STUDY: The present investigation aimed to investigate the anxiolytic, antidepressant and aphrodisiac potentials of methanol leaves extract of A. hookerianum (MEAH) in Swiss albino mice.

    MATERIALS & METHODS: Swiss albino mice (20-30 g) were orally administrated with MEAH at the doses ranging from 100 to 400 mg/kg, b.w. The elevated plus maze (EPM) and hole board test (HBT) were performed to determine the anxiolytic activity and the forced swimming test (FST) and tail suspension test (TST) were performed to determine the antidepressant activity of MEAH. Besides, the aphrodisiac activity of MEAH was conducted through the mounting behaviour and orientation behaviour analysis. Diazepam (1 mg/kg, b.w., i.p.) for EPM and HBT; fluoxetine HCl (20 mg/kg, b.w., p.o.) for FST and TST, and sildenafil (5 mg/kg, b.w., p.o.) for the mounting behaviour analysis and orientation behaviour analysis were used as reference drugs.

    RESULTS: The administration of the MEAH produced a strong (p 

  12. Effects of drying methods on oxidative stability of roselle seed oil (Hibiscus Sabdariffa): an optimization approach
    Jahurul MHA, Shian OK, Sharifudin MS, Hasmadi M, Lee JS, Mansoor AH, et al.
    J Food Sci Technol, 2021 Mar;58(3):902-910.
    PMID: 33678873 DOI: 10.1007/s13197-020-04604-1
    The objective of this study was to optimize the extraction of oil from pre-dried roselle seeds using response surface methodology (RSM). We also determined the oxidative stability of oil extracted from oven and freeze-dried roselle seed in terms of iodine value (IV), free fatty acid (FFA) value, peroxide value (PV), P-anisidine and total oxidation values (TOTOX value). The RSM was designated based on the central composite design with the usage of three optimum parameters ranged from 8 to 16 g of sample weight, 250-350 mL of solvent volume, and 6-8 h of extraction time. The highest oil yielded from roselle seed using the optimization process was 22.11% with the parameters at sample weight of 14.4 g, solvent volume of 329.70 mL, and extraction time of 7.6 h. Besides, the oil extracted from the oven dried roselle seed had the values of 89.04, 2.11, 4.13, 3.76 and 12.03 for IV, FFA, PV, P-anisidine, and TOTOX values, respectively. While for the oil extracted from freeze-dried roselle seed showed IV of 90.31, FFA of 1.64, PV of 2.47, P-anisidine value of 3.48, and TOTOX value of 8.42. PV and TOTOX values showed significant differences whereas; IV, FFA, and P-anisidine values showed no significant differences between the oven and freeze-dried roselle seed oils.
  13. Mercury in dental amalgam: Are our health care workers at risk?
    Sahani M, Sulaiman NS, Tan BS, Yahya NA, Anual ZF, Mahiyuddin WR, et al.
    J Air Waste Manag Assoc, 2016 Nov;66(11):1077-1083.
    PMID: 27192328 DOI: 10.1080/10962247.2016.1188866
    Dental amalgam in fillings exposes workers to mercury. The exposure to mercury was investigated among 1871 dental health care workers. The aim of the study was to evaluate the risk of mercury exposure among dental compared to nondental health care workers and to determine other risk factors for mercury exposure. Respondents answered questionnaires to obtain demographic, personal, professional, and workplace information and were examined for their own amalgam fillings. Chronic mercury exposure was assessed through urinary mercury levels. In total, 1409 dental and 462 nondental health care workers participated in the study. Median urine mercury levels for dental and nondental health care workers were 2.75 μg/L (interquartile range [IQR] = 3.0175) and 2.66 μg/L (IQR = 3.04) respectively. For mercury exposure, there were no significant risk factor found among the workers involved within the dental care. The Mann-Whitney test showed that urine mercury levels were significantly different between respondents who eat seafood more than 5 times per week compared to those who eat it less frequently or not at all (p = 0.003). The urinary mercury levels indicated significant difference between dental workers in their practice using squeeze cloths (Mann-Whitney test, p = 0.03). Multiple logistic regression showed that only the usage of cosmetic products that might contain mercury was found to be significantly associated with the urinary mercury levels (odds ratio [OR] = 15.237; CI: 3.612-64.276). Therefore, mean urinary mercury levels of health care workers were low. Exposure to dental amalgam is not associated with high mercury exposure. However, usage of cosmetic products containing mercury and high seafood consumption may lead to the increase of exposure to mercury.

    IMPLICATIONS: Exposure to the high levels of mercury from dental amalgam can lead to serious health effects among the dental health care workers. Nationwide chronic mercury exposure among dental personnel was assessed through urinary mercury levels. Findings suggest low urinary mercury levels of these health care workers. Exposure to dental amalgam is not associated with high mercury exposure. However, the usage of cosmetic products containing mercury and high seafood consumption may lead to the increase of exposure to mercury.
  14. Sterols as biomarkers in the surface microlayer of the estuarine areas
    Alsalahi MA, Latif MT, Ali MM, Dominick D, Khan MF, Mustaffa NI, et al.
    Mar Pollut Bull, 2015 Apr 15;93(1-2):278-83.
    PMID: 25682566 DOI: 10.1016/j.marpolbul.2015.01.011
    This study aims to determine the concentration of sterols used as biomarkers in the surface microlayer (SML) in estuarine areas of the Selangor River, Malaysia. Samples were collected during different seasons through the use of a rotation drum. The analysis of sterols was performed using gas chromatography equipped with a flame ionisation detector (GC-FID). The results showed that the concentrations of total sterols in the SML ranged from 107.06 to 505.55 ng L(-1). The total sterol concentration was found to be higher in the wet season. Cholesterol was found to be the most abundant sterols component in the SML. The diagnostic ratios of sterols show the influence of natural sources and waste on the contribution of sterols in the SML. Further analysis, using principal component analysis (PCA), showed distinct inputs of sterols derived from human activity (40.58%), terrigenous and plant inputs (22.59%) as well as phytoplankton and marine inputs (17.35%).
  15. Surfactants in the sea-surface microlayer and atmospheric aerosol around the southern region of Peninsular Malaysia
    Jaafar SA, Latif MT, Chian CW, Han WS, Wahid NB, Razak IS, et al.
    Mar Pollut Bull, 2014 Jul 15;84(1-2):35-43.
    PMID: 24930738 DOI: 10.1016/j.marpolbul.2014.05.047
    This study was conducted to determine the composition of surfactants in the sea-surface microlayer (SML) and atmospheric aerosol around the southern region of the Peninsular Malaysia. Surfactants in samples taken from the SML and atmospheric aerosol were determined using a colorimetric method, as either methylene blue active substances (MBAS) or disulphine blue active substances (DBAS). Principal component analysis with multiple linear regressions (PCA-MLR), using the anion and major element composition of the aerosol samples, was used to determine possible sources of surfactants in atmospheric aerosol. The results showed that the concentrations of surfactants in the SML and atmospheric aerosol were dominated by anionic surfactants and that surfactants in aerosol were not directly correlated (p>0.05) with surfactants in the SML. Further PCA-MLR from anion and major element concentrations showed that combustion of fossil fuel and sea spray were the major contributors to surfactants in aerosol in the study area.
  16. Distribution of surfactants along the estuarine area of Selangor River, Malaysia
    Alsalahi MA, Latif MT, Ali MM, Magam SM, Wahid NB, Khan MF, et al.
    Mar Pollut Bull, 2014 Mar 15;80(1-2):344-50.
    PMID: 24373668 DOI: 10.1016/j.marpolbul.2013.12.019
    This study aims to determine the levels of methylene blue active substances (MBAS) and ethyl violet active substances (EVAS) as anionic surfactants and of disulphine blue active substances (DBAS) as cationic surfactants in the surface microlayer (SML) around an estuarine area using colorimetric methods. The results show that the concentrations of surfactants around the estuarine area were dominated by anionic surfactants (MBAS and EVAS) with average concentrations of 0.39 and 0.51 μmol L⁻¹, respectively. There were significant between-station differences in surfactant concentrations (p<0.05) with higher concentrations found at the stations near the sea. The concentration of surfactants was higher during the rainy season than the dry season due to the influence of runoff water. Further investigation using total organic carbon (TOC) and total organic nitrogen (TON) shows that there is a significant correlation (p<0.05) between both anionic and cationic surfactants and the TON concentration.
  17. Monsoonal variations in atmospheric surfactants at different coastal areas of the Malaysian Peninsula
    Jaafar SA, Latif MT, Razak IS, Shaharudin MZ, Khan MF, Wahid NBA, et al.
    Mar Pollut Bull, 2016 Aug 15;109(1):480-489.
    PMID: 27230987 DOI: 10.1016/j.marpolbul.2016.05.017
    This study determined the effect of monsoonal changes on the composition of atmospheric surfactants in coastal areas. The composition of anions (SO4(2-), NO3(-), Cl(-), F(-)) and the major elements (Ca, K, Mg, Na) in aerosols were used to determine the possible sources of surfactants. Surfactant compositions were determined using a colorimetric method as methylene blue active substances (MBAS) and disulphine blue active substances (DBAS). The anion and major element compositions of the aerosol samples were determined by ion chromatography (IC) and inductively coupled plasma mass spectrometry (ICP-MS), respectively. The results indicated that the concentrations of surfactant in aerosols were dominated by MBAS (34-326pmolm(-3)). Monsoonal changes were found to significantly affect the concentration of surfactants. Using principal component analysis-multiple linear regressions (PCA-MLR), major possible sources for surfactants in the aerosols were motor vehicle emissions, secondary aerosol and the combustion of biomass along with marine aerosol.
  18. Fulltext Calibration Model of a Low-Cost Air Quality Sensor Using an Adaptive Neuro-Fuzzy Inference System
    Alhasa KM, Mohd Nadzir MS, Olalekan P, Latif MT, Yusup Y, Iqbal Faruque MR, et al.
    Sensors (Basel), 2018 Dec 11;18(12).
    PMID: 30544953 DOI: 10.3390/s18124380
    Conventional air quality monitoring systems, such as gas analysers, are commonly used in many developed and developing countries to monitor air quality. However, these techniques have high costs associated with both installation and maintenance. One possible solution to complement these techniques is the application of low-cost air quality sensors (LAQSs), which have the potential to give higher spatial and temporal data of gas pollutants with high precision and accuracy. In this paper, we present DiracSense, a custom-made LAQS that monitors the gas pollutants ozone (O₃), nitrogen dioxide (NO₂), and carbon monoxide (CO). The aim of this study is to investigate its performance based on laboratory calibration and field experiments. Several model calibrations were developed to improve the accuracy and performance of the LAQS. Laboratory calibrations were carried out to determine the zero offset and sensitivities of each sensor. The results showed that the sensor performed with a highly linear correlation with the reference instrument with a response-time range from 0.5 to 1.7 min. The performance of several calibration models including a calibrated simple equation and supervised learning algorithms (adaptive neuro-fuzzy inference system or ANFIS and the multilayer feed-forward perceptron or MLP) were compared. The field calibration focused on O₃ measurements due to the lack of a reference instrument for CO and NO₂. Combinations of inputs were evaluated during the development of the supervised learning algorithm. The validation results demonstrated that the ANFIS model with four inputs (WE OX, AE OX, T, and NO₂) had the lowest error in terms of statistical performance and the highest correlation coefficients with respect to the reference instrument (0.8 < r < 0.95). These results suggest that the ANFIS model is promising as a calibration tool since it has the capability to improve the accuracy and performance of the low-cost electrochemical sensor.
  19. Long term assessment of air quality from a background station on the Malaysian Peninsula
    Latif MT, Dominick D, Ahamad F, Khan MF, Juneng L, Hamzah FM, et al.
    Sci Total Environ, 2014 Jun 1;482-483:336-48.
    PMID: 24662202 DOI: 10.1016/j.scitotenv.2014.02.132
    Rural background stations provide insight into seasonal variations in pollutant concentrations and allow for comparisons to be made with stations closer to anthropogenic emissions. In Malaysia, the designated background station is located in Jerantut, Pahang. A fifteen-year data set focusing on ten major air pollutants and four meteorological variables from this station were analysed. Diurnal, monthly and yearly pollutant concentrations were derived from hourly continuous monitoring data. Statistical methods employed included principal component regression (PCR) and sensitivity analysis. Although only one of the yearly concentrations of the pollutants studied exceeded national and World Health Organisation (WHO) guideline standards, namely PM10, seven of the pollutants (NO, NO2, NOx, O3, PM10, THC and CH4) showed a positive upward trend over the 15-year period. High concentrations of PM10 were recorded during severe haze episodes in this region. Whilst, monthly concentrations of most air pollutants, such as: PM10, O3, NOx, NO2, CO and NmHC were recorded at higher concentrations between June and September, during the southwest monsoon. Such results correspond with the mid-range transport of pollutants from more urbanised and industrial areas. Diurnal patterns, rationed between major air pollutants and sensitivity analysis, indicate the influence of local traffic emissions on air quality at the Jerantut background station. Although the pollutant concentrations have not shown a rapid increase, an alternative background station will need to be assigned within the next decade if development projects in the surrounding area are not halted.
  20. Coastal meteorology on the dispersion of air particles at the Bachok GAW Station
    Rahim HA, Khan MF, Ibrahim ZF, Shoaib A, Suradi H, Mohyeddin N, et al.
    Sci Total Environ, 2021 Aug 15;782:146783.
    PMID: 33838363 DOI: 10.1016/j.scitotenv.2021.146783
    Meteorology over coastal region is a driving factor to the concentration of air particles and reactive gases. This study aims to conduct a research to determine the level of year-round air particles and the interaction of the meteorological driving factors with the particle number and mass in 2018, which is moderately influenced by Southeast Asian haze. We obtained the measurement data for particle number count (PNC), mass, reactive gases, and meteorological factors from a Global Atmospheric Watch (GAW) station located at Bachok Marine Research Center, Bachok, Kelantan, Malaysia. For various timeseries and correlation analyses, a 60-second resolution of the data has been averaged hourly and daily and visualized further. Our results showed the slight difference in particle behavior that is either measured by unit mass or number count at the study area. Diurnal variations showed that particles were generally high during morning and night periods. Spike was observed in August for PM2.5/PNC2.5 and PM10/PNC10 and in November for PMCoarse/PNCCoarse. From a polar plot, the particles came from two distinct sources (e.g., seaside and roadside) at the local scale. Regional wind vector shows two distinct wind-blown directions from northeast and southwest. The air mases were transported from northeast (e.g., Philippines, mainland China, and Taiwan) or southwest (e.g., Sumatra) region. Correlation analysis shows that relative humidity, wind direction, and pressure influence the increase in particles, whereas negative correlation with temperature is observed, and wind speed may have a potential role on the decline of particle concentration. The particles at the study area was highly influenced by the changes in regional wind direction and speed.
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