Dissertations/Theses - Department of Civil Engineering
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Item Spatio-temporal pollution trend of Buriganga river(Department of Civil Engineering, BUET, 2023-06-20) Farah Ahmed Turin; Md. Delwar Hossain, Dr.This study focused on the identification of some water quality parameters of Buriganga river adjacent to Dhaka City. In this study, a portion of Buriganga river from Showary ghat to Pagla has been selected as the study reach to assess the existing water quality during the wet season of the year 2022 and dry season of the year 2023. Water samples were collected from twelve monitoring locations along this reach during that period. Different water quality parameters have been assessed in this study including pH, DO, EC, Color, COD, BOD5, NH3-N, H2S and Cl-. Heavy metals (Chromium, Lead) have been measured during the month of March, 2023. In-situ test was performed for some parameters like pH, DO and EC. Spatial and temporal variation of Buriganga river water quality have been assessed in this study through graphical analysis and comparing with previous studies. DO concentration was higher in the rainy season than in dry season. Maximum dissolve oxygen in rainy season was found 4.24 mg/L at Posta in October 2022. Minimum DO was found in Showary ghat in March 2023. EC was observed 169 to 185 μS /cm in wet season and 542 to 852 μS /cm in dry season. BOD5 in the rainy season is lower than dry season. Maximum BOD5 was found 128 mg/l in March 2023 at Pagla and minimum BOD5 was found 1.0 mg/l in October 2022 at Showary ghat. COD value was found 8.0 to 42.0 mg/L in the rainy season; whereas in dry season it was much higher from 51.0 to 316.0 mg/L. Average BOD5 to COD ratio was found less than 0.30, which indicates that the amount of non-biodegradable organic matter is higher than biodegradable organic matter in Buriganga river. Chloride concentration was found lower (9.0 to 17.0 mg/L) in wet season and during dry season the value rises 30.0 to 67.0 mg/L. Other parameters like NH3-N, H2S are higher in dry season than rainy season. Pollution load in Buriganga river increases during dry season and washed out during monsoon. Pollution trend from previous data indicates that pollution load has increased during the last 50 years. Minimum DO concentration decreased almost six times during 1968 to 2023 in Buriganga river, Maximum Chloride concentration has increased around 12 times during that period and change of maximum BOD5 concentration was Observed almost 14 times during last 23 years(2000-2023).Item Estimation of suspended sediment concentration using remote sensing and water quality trend analysis of Jamuna river at Bahadurabad station(Department of Civil, 2023-04-30) Farhana, Kabir; Delwar Hossain, Dr. Md.Assessment of suspended sediment concentration in running streams is crucial for a variety of applications, including environmental issues, hydraulic structure performance monitoring, and agricultural land use. Conventional methods for the measurement of suspended sediment load, both in-situ and in the lab, are expensive relative to the use of remotely sensed data. Both aerial photography and satellite imagery have been used to map suspended sediment. This study investigated the applicability of open-access Landsat Enhanced Thematic Mapper (ETM+) images in estimating the SSC of the Jamuna. Multiple- temporal Landsat 7 ETM+ images were processed to extract Digital Numbers (DN) of pixels corresponding to Bahadurabad station of the Jamuna River. The DNs were converted to radiance and ultimately to top-of-atmosphere (ToA) reflectance. Since mostly clear scenes were used, in situ atmospheric correction was ignored. The ToA values for Landsat-7 bands 1-4, which sense electromagnetic radiation of 0.45-0.52, 0.52-0.60, 0.63-0.69 and 0.76-0.90 μm respectively,were combined with corresponding measured values of SSC, procured from historical data archives of BWDB, between the years 2000 to 2015 for determination of statistical relationship between them. R2 for bands 1, 2, 3 and 4 were 0.61, 0.59, 0.54 and 0.54 respectively. The results from analysis showed that Coefficient of Determination (R2) value of band 1 (Blue) presented the best relationship - therefore chosen as the best SSC indicator. Scatter plot of predicted SSC values from a polynomial equation based on band 1 against in situ values of SSC generated strong positive coefficient of determination of 0.91 and Root Mean Square Error (RMSE) of 79.5 ppm. Mann-Kendall and Sen’s slope test are applied on the water quality parameters from 2002-2021 for trend analysis. Further findings revealed that increasing trend in EC, Clˉ, salinity and TDS. In last 15 years chloride concentration increases about 2 times, EC increases about 4.5 times, TDS increases about 5 times and salinity increases about 3.5 times respectively. Higher amount of chloride, TDS, EC and salinity is found in pre- monsoon season. As in the pre-monsoon due to sea level rise salinity as well as chloride concentration increases whereas in the monsoon fresh water flow increases chloride concentration, salinity and EC reduce. There is also some relationship made between EC-Cl¯, TDS- Cl¯ and TDS-EC.Item Minimum thickness of solid RC floor slab to mitigate walking induced vibration discomfort(2024-05-11) Tazwar Bakhtiyar ZahidPresent advancements in concrete technology have resulted in an increased strength of concrete supplemented by light weight characteristics. At the same time they have also become prone to walking induced vibration and associated discomfort to occupants. The existing ACI serviceability limit often falls short on deciding the minimum thickness of slabs to circumvent walking induced vibration discomfort, necessitating a greater slab thickness. In the present study a finite element approach has been used to study the dynamic response of RC slab system under single person and multiple person walking excitation. This study has been conducted on symmetric slab system. A linear time history approach has been used to investigate the behavior of solid reinforced concrete slab systems with column line beams. A finite element analyses model of an intermediate floor of a multi-story building with 3 3 slab panels has been developed. The adopted methodology has also been validated against the results obtained from past experiments. The slab system was subjected to single person and multiple person walking excitation. The response was studied in terms of the acceleration response of the central node of the central span and the frequency data obtained by converting the acceleration response to frequency domain using Fast Fourier Transformation. The responses have been compared for different thickness against the ACI serviceability limit, as well as limits suggested in other design guides. For single person walking excitation, the responses have been observed for different values of span length, slab thickness, aspect ratio and the walking direction. It was observed that the walking direction did not have any influence in the response of the slab. The response however showed variation with the change in other parameters. It appeared that, the ACI serviceability limit might be insufficient in deciding the minimum slab thickness for slab panels with larger slab spans and aspect ratio. For multiple person synchronized walking excitation on square panels, the acceleration response showed variation with the change in studied slab length and slab thickness. The minimum slab thickness required for the response to come below the allowable acceleration limit was greater than the ACI serviceability limit for all the spans studied. However, such a loading condition is less common, unless people are engaged in rhythmic activities. Thus, a study on non-synchronized walking excitation has been conducted. For such a walking excitation, the required minimum slab thickness was also greater than the ACI serviceability limit for the spans studied when compared against the allowable acceleration limit suggested in CRSI design guide. Based on the observations from the study, guidelineson selecting slab thickness are proposed for single person and multiple person walking. For single person walking, response was obtained for slab panels with varying aspect ratio. The response for multi-person walking excitation was obtained for square slab panels only. It is expected that the suggested guideline will help engineers in selecting the minimum slab thickness based on the span length of the slab system that will circumvent walking induced vibration discomfort.Item In-plane cyclic load test of masonry wall with RC overlay on one face(Department of Civil Engineering, 2022-11-13) Izharul Haque Azad, Md.; Raquib Ahsan, Dr.Unreinforced brick masonry buildings, a prevalent structural typology for residential buildings in Bangladesh, require attention to improve their seismic performance. These buildings or their wall components are rarely designed to resist lateral loads. In seismic events, they suffer severe damage causing loss of livesand properties. That is why their seismic retrofitting and strengthening is very important for the seismic resilience of Bangladesh. This research presents an experimental investigationof seismic retrofitting of unreinforced masonry walls and its findings. In-plane cyclic loading tests,acting simultaneously withgravity loads, were conducted on a series of half-scale masonry walls of thickness 127 mm. The walls were constructed to replicate a full-scale 10 in. masonry wall with English bond conventionally used in our country. Samples with two aspect ratios (height to length ratio), namely 1.0 (1524mm height x 1524 mm length)and 0.75 (1524 mm height x 2032 mm length),were prepared and tested under lateral cyclic loadings and their response and failure modes were observed. Then the failed samples were retrofitted and the two others were directly strengthened with a 40 mm thick RC overlay on one face having 6 mm dia. rebars provided @75 mm c/c in both directions. The cage was anchored to the wall with the help of hooks and to the base using epoxy. The lateral load carrying capacity of short walls (AR=1.0) was increased by 3.2 times for both the directlystrengthened sample and the sample retrofitted after failure.For long walls (AR=0.75), the capacities increased3.43 times and 2.85 times,respectively. The capability of undergoing a large deformation prior to failure was also improved remarkably due to the incorporation of RC overlay. The dissipated energyfor directly strengthened short wallswas11.56 timesand for short walls retrofitted after failure was 9.1 timesof that of the control specimens.For directly strengthened long walls,the dissipated energy was 12.34 times and that for long walls retrofitted after failure was 2.93 times. The ductility was also improved by a factor of 4.3 (for samplesretrofitted after failure)and 7.45 (for direct strengthened samples)for short walls and 3.4 (for samples retrofitted after failure) and 8.9 (for direct strengthened samples) times for long wallsin comparison to the control samples. The RC overlay also influenced hysteresis damping. The hysteresis damping ratio for short wall assembly ranges from 7.85% to 16.61 % when retrofitted and 10.77 % to 17.29 % when directly strengthened. In the case of the long wall control specimen, the damping ratio was 5.07 % to 13.7 % which increased to the range of 13.01 % to 19.16 % when retrofitted and 11.89 % to 31.83 % when directly strengthened. The failure modes of the walls also changed from rocking and sliding to rocking and flexural compression, and in some cases, it was the formation of diagonal cracks. The strengthened samples exhibit a rocking type of failure and there was also a sign of corner crushing as the cracks propagated towards the toe. The test results suggest that the RC overlay improved the seismic response of unreinforced masonry (URM) walls in terms of all the parameters stated above. Regarding the influence of aspect ratio, it was found that the long walls exhibited better performance compared to the short walls with an aspect ratio equal to one.Item Application of machine learning in analyzing severities of double vehicle crashes in Bangladesh(Department of Civil Engineering, 2023-03-20) Sadia, Mohsin; Rahman, Dr. Md. MizanurRoad traffic crashes have become one of the leading causes of death worldwide. Bangladesh, a developing country, is rapidly becoming a major victim of road accidents. Due to traffic crashes, different types of injuries eventuate depending on the severity level of the crashes. Double vehicle crashes are the most critical type of road accidents that have the potential to cause serious injuries and fatalities. Unfortunately, Bangladesh is still in nascent stage in dealing with road accidents, especially for double vehicle crashes. A precise prediction of crash severity in road accidents significantly improves traffic safety. Therefore, there has recently been a tactical shift among safety researchers to apply machine learning (ML) algorithms to estimate crash severity due to their superior predictive ability. Although there have been an increasing number of applications of machine learning methods in crash severity research, however there is a limited applicability of these methods in estimating the severity of a double vehicle crashes. As a result, this study aimed to apply machine learning algorithms in predicting double vehicle crash severities in the context of Bangladesh. The aim of this study is to compare the predicted performance of numerous machine learning and traditional statistical regression techniques in modeling double vehicle crash severities, as well as to identify the contributing components and how they impact crash severity prediction. Using Dhaka's most recent crash record collected from Accident Research Institute (ARI), BUET (2017-2020), this study employed classification and regression tree, support vector machine, random forest, adaptive boosting, logistic regression, and soft voting classifier-based hybrid models. This study compared the performance of logistic regression and other machine learning classifiers using the most commonly known evaluation criteria: Accuracy (ACC), Receiver Operating Characteristics (ROC) Curve, and Area Under the Curve (AUC) Value. The comparison of predictive performance revealed that the hybrid model, built on logistic regression, random forest, and adaptive boosting, outperforms other individual models with a subset of twenty explanatory variables and with an accuracy of 75% and an AUC score of 0.71. With the same subset of features, random forest performs better with an accuracy of 70% and an AUC score of 0.69 within the individual models. This study uses the SHAP (Shapley Additive Explanation) methodology to determine how well the features contribute to the severity prediction, thus finding influential factors. SHAP Global Feature Importance represents the marginal contribution of each feature in the prediction. SHAP Local Explanation identifies how the contributing factors affect double vehicle crash severities. According to the SHAP (Shapley Additive Explanation) technique, the most significant elements of double vehicle crash severities are the day of the week, vehicle type, time of day, vehicle maneuver, road geometry and they have important contribution in predicting crash severities by an average of 10.2, 4.8, 4.6, 3.8 and 2.9 percentage points respectively. This means that the factor day of week alone contributed in predicting whether the double vehicle crash severity would be fatal or not by an average of 10.2 percentage points. In addition, vehicle type is another most critical variables in predicting double vehicle crash severities whether it would be fatal or not by an average of 4.8 percentage points.Item Effectiveness of vetiver for landslide prevention in hilly areas of Chattogram metropolitan(Department of Civil, 2022-09-27) Mohiuddin, Ahmed; Islam, Prof. Dr. Mohammad SharifulHills of tertiary-aged sedimentary rocks prone to landslides and surface erosion characterize the Chattogram metropolitan cityscape. The primary focus of this study is the application of a vegetative method using vetiver grass (Chrysopogon zizanioides) on this terrain to reduce soil loss, improve slope stability, and increase landslide resistance. In addition, vetiver's effect on sediment deposition in the city drainage system due to slope erosion has also been investigated. Three vetiver-planted plots and a bare hill slope plot were developed on a selected urban hill slope section (Tigerpass Hill). The growth performance was evaluated for three consecutive rainy seasons, from July 2019 to August 2021. The slope top soil up to 1.5 m depth was silty loam (CL-ML), having intermediate dispersive characteristics, low nutrient contents, a pH of 6.4, and an average slope angle of 34.80. Simulating artificial rain, the experimental field method was mirrored in the scaled-down mode. The field study found that vetiver root-shoot growth outperformed native herbs and shrubs in developing a widespread root network on slopes. The generation of surface runoff was noticed when slope moisture neared the limit of 26-27% with roughly 90% saturation under varying rainfall intensities. Average sediment output on the vetiver slope decreased from 63 t/ha to 18 t/ha in 2021, despite annual rainfall increasing by 2 to 10 times that of 2019 and the estimated cumulative vetiver root coverage increasing from 13% to 44%. Within this period, erosionmeasurements indicated that in a liter of turbid runoff water in 2019, the highest 1.81 g of sediment yield was reduced to 0.5 g (a 73% reduction) in 2021. Moreover, at rainfall intensities greater than 35 mm/h, the trend for silt loss exhibited an exponential rise. Four developed and experimentally fitted equations for four plots demonstrated a linear regression relationship between sediment yield and rainfall intensity. The vetiver growth rate was sufficient to offset the effects of the rising trend in yearly rainfall influencing surface erosion and sediment loss. Therefore, vetiver was found to be a good bioengineering resource for reducing soil loss from mass surface runoff. In the small-scale model, the average sediment loss differential between a bare and vegetated slope was 2.18 times, while that for the hill slope was 1.22 times, warranting an actual field study for better accuracy in erosion measurement. This study also identifies that the installation of approximately 70,000 m3 of silt traps on the foothills, where major city canals originate, has a beneficial impact on reducing sediment burdens on the city drainage system. The combined effect of vetiver plantation and silt trap installation was expected to result in a 72% decrease in sediment drop in the municipal drainage system for the observed period of 2019 to 2021. This decrement may significantly relieve the municipality's overstretched drainage maintenance load. Thus, vetiver performed outstandingly in resolving the long-standing siltation issue associated with city drainage systems. A PLAXIS 3D numerical analysis of field slopes for bare and vetiver root-reinforced conditions with variable rainfall intensities between 17.2 and 41.5 mm/h revealed that the mean slope FS improvement between rooted and non-rooted states was 11% by 108 days in 2019, rising to 21% by 470 days in 2020. Thus, vetiver plantation along hill slopes reduces soil erosion and increases slope stability, making this bioengineering technique effective for reducing the landslide susceptibility of hills.Item Assessment of characteristics of fecal sludge from different sources and its effect on dried sludge(Department of Civil Engineering(CE), BUET, 2023-02-11) Sirajul Islam, Md.; Ali, Dr. Muhammad AshrafThe purpose of this study was to evaluate the characteristics of raw fecal sludge emptied from different types of onsite sanitation facilities, and to assess its effect on the operation of FSTPs. Raw FS samples emptied from different types of containments were collected from Dhaka and Sakhipur (Tangail), and were analyzed for a wide range of parameters, including pH, EC, TS, TDS, TSS, COD, NH4+, NO3- and PO43-. The raw FS samples were classified into four broad categories: (a) Sakhipur Public Septic Tanks; (b) Sakhipur household pits; (c) Dhaka household septic tanks; and (d) Dhaka public septic tank. The mean pH values of the raw fecal sludge samples were in the neutral range, varying from 6.84 to 7.46. The EC values of the FS samples ranged from 2.68 mS/cm to 4.27 mS/cm, with no clear correlation with TDS values, possibly due to the presence of non-ionized dissolved solids in FS. The TSS concentration of FS samples from household pits in Sakhipur were also found to be significantly higher, possibly due to the leaching of water from pits. The mean COD and TSS values were 2,405 mg/l and 4,220 mg/l, respectively. The ammonium (mean 244 mg/l) and phosphate (mean 170 mg/l) concentrations indicate that FS could be an excellent source of nutrient for use in agriculture. No clear trend was observed between the source of FS and their characteristics. However, the COD values of FS samples collected from public septic tanks and pits were found to be significantly higher than those collected from containments in Dhaka. Compared to the reported raw FS characteristics from African regions (where dry toilets and use of toilet papers are common), the raw FS samples collected in this study are much more dilute. Because of lower TSS contents of raw FS, the estimated solids loading rates for the unplanted drying beds in Sakhipur FSTP have been found to be significantly lower than those typically used in the design of unplanted drying beds. It appears that introduction of settling-thickening tanks, as a pre-treatment unit, could significantly improve treatment efficiency and reduce the land requirements for FSTPs employing drying beds. Dried FS samples produced in unplanted drying beds were collected from Sakhipur and Faridpur FSTP, and were analyzed for moisture content, nutrient and heavy metal contents. It was found that significant moisture content reduction could be achieved through the storage of dried fecal sludge. The ammonium nitrogen content (mean 215 mg/kg) and phosphate content (117 mg/kg) suggest that resource recovery from dried FS would be beneficial. Heavy metal (Pb, Cd, Cr, Cu, Ni, Zn) contents of the dried FS samples were significantly lower than the corresponding Bangladesh standards for sludge. The mean calorific values of dried FS samples varied over a relatively narrow range of 8.7 to 13.4 MJ/kg. The dried FS samples from public septic tanks appears to have a slightly higher calorific values than those from household septic tanks and pits. Calorific values of dried FS calculated from elemental composition using the modified Dulong formula appear to provide results closer to the experimental values. The relatively lower calorific values of dried FS appear to be a constraint for energy recovery through combustion. Considering the properties of FS, co-composting, which is widely used in Bangladesh and worldwide, is an excellent option for the recovery of resources from FS. Since the characteristics of FS varies significantly due to a range of factors, including type of containment, environmental conditions (e.g., infiltration capacity of soil), usage (e.g., use/volume of flush water) and empting methods, more extensive studies should be carried out to assess the characteristics of raw FS and its implication on the design/ operation of FSTPs and quality of end products (e.g., compost or solid fuel).Item Cost optimization of deck girder system of post tensioned i-girder bridge for different number of lanes(Department of Civil Engineering(CE), BUET, 2022-09-28) Nazmus Sakib, Md.; Ahsan, Dr. RaquibCost optimization of deck girder system of post-tensioned I-girder bridge for different number of lanes is presented in this thesis. The main objective is to find the optimized deck girder configurations which satisfy all the safety and serviceability criteria while considering the cost of materials, fabrication installation, and labor. For a particular bridge superstructure with specific span length, lane width and footpath width, the design variables considered for this thesis are number of girder, c/c spacing of girder, various cross-sectional dimensions of the deck slab and girder, type and number of cables, applied force on cables, and ordinary reinforcement for deck slab and girder. Bounds are applied to the design variables based on code-specified guidelines and geometric requirements. Constraints for the design are applied using AASHTO LRFD Bridge Design Specifications, 2017, and geometric requirements. The bridge design optimization is a very complex problem with lots of design variables, non-linear constraints long calculations, and lots of local minimums, making it very difficult to find the global optimum solution. So, to solve this complex problem Differential Evolution (DE) algorithm from the SciPy library is used, which is a widely used global optimization algorithm used in different fields and very easy to implement. A spreadsheet is used to calculate everything involved in design calculation and to input design variables, bounds, constraints, and objective functions. Then a computer program written in Python is used to link the spreadsheet with the DE algorithm and solve the problem. The formulated spreadsheet and program were then used to optimize conventionally used design where the output results show around 15~20% cost reduction in optimized design from unoptimized design for 100 ft, 120 ft, 140 ft, and 160 ft span, for both 2-lane and 4-lane bridges. The optimized design also shows around 11~13% cost improvement from a 100 ft span where, a few constraints are applied to resemble the field condition (maximum height limit 0.055L for deck plus girder, maximum applicable stress on cable 0.75fpu, allowable maximum compressive stress at transfer 0.60f’ci, allowable bottom stress at service limit state -0.109 ksi (compression)). The study found that the cost per unit area for 2-lane bridges is 1.83~2.15% more than the cost per unit area for 4-lane bridges. This study also compares Ahsan et al. (2012) results, where it shows that cost reduction of 10% from existing design using DE and 21% cost increase from EVOP optimization results. The study also covered a detailed parametric study on different design variables and how every variable affects the overall superstructure design which will be very helpful for practical design.Item Influence of locally available cement types on mechanical strength and durability performance of concrete(Department of Civil Engineering, 2022-04-26) Shifat Hossain Khan, Mohammad; Siddique, Dr. Mohammad Al AminThis research is planned to figure out the effect of different cement types on the mechanical and durability properties of concrete. Four types of cement are commonly used in Bangladesh's rapidly growing construction sector.So, it is very essential to determine the specific type of cement that will be efficient considering its strength, economic, and durability aspects. Four types of cement [CEM I, CEM II/(A-M/S-V-L), CEM II/(B-M/S-V-L), CEM II/(B-L)] commonly used in Bangladesh have been considered in this study. Their usage has recently been on the increase as with the vast infrastructure development. The production of CEM I, namely (OPC), decreases due to the concern over CO2 emissions. A specific portion of clinker in the cement content is substituted with mineral additions such as limestone, fly ash, and slag, resulting in CEM II types, and thereby,the cost is reduced. This comprehensive experimental study includes the determination of mechanical properties such as concrete compressive strength, tensile strength, and modulus of elasticity using four types of cement and four different w/c ratios (0.40,0.45,0.55,0.65). This results in sixteen concrete mixes, and obtained results are compared to one another. In addition, the durability property in terms of the rapid chloride permeability test (RCPT) for different mixes has been evaluated to assess the suitable cement for concrete production. From the test results, it is observed that the generalized pattern for compressive strength of the considered four different cement concrete is CEM Ⅰ>CEM Ⅱ/(A-M)> CEM Ⅱ/ (B-L)> CEM Ⅱ/(B-M). Concrete made with CEM-I cement shows a 20% enhancement in compressive strength in comparison to CEM II/B-M having a w/c ratio of 0.40. This increase is 50% when the w/c ratio is considered 0.65. Concrete made with CEM II/B-L cement shows a higher corrosion potential while CEM I result moderate and CEM II/A-M and CEM II/B-M provide lower corrosion potential for the considered mixes. Materials cost for concrete result in comparable amount with CEM I on the higher side and CEM II/B-M on the lower side. The obtained results show that CEM II/A-M may be considered anefficient cement type in concrete in terms of cost, compressive strength, and durability. However, the scope of this study is limited to the results of the considered 16 concrete mixes with the considered cement types.Item Characterizing particulate air pollution in rural areas of Bangladesh using a network of low-cost sensors(Department of Civil Engineering, 2023-07-31) Sanjeev, Delwar; Saha, Dr. Provat KumarThis study presents a comprehensive study on characterizing fine particulate matter (PM2.5) pollution levels across Bangladesh through an utilization of a network of low-cost sensors. Prior to deployment in rural sites, the low-cost sensors were calibrated against a reference PM2.5 monitor (Beta Attenuation Monitor, BAM)at DoE continuous air monitoring stations (CAMS). The calibration process involved continuous data collection for one month each during the dry and wet seasons. This rigorous calibration ensured the accuracy and reliability of the collected data. Over a four-month period, comprising two months each in the dry and wet seasons, continuous measurements were collected at 20 rural sites spread across the country. The raw data gathered from these rural deployments were then corrected using calibration models developed from the co-location deployments. The calibration of the low-cost sensors against the reference monitor showed excellent agreement, with consistent sensor-to-sensor performance throughout the calibration process. The linear calibration models achieved a R2 of 0.85 - 0.9, and the normalized root mean square error (RMSE) ranged between 10-15%. The average PM2.5 levels measured across the 20 rural sites were remarkably higher, ranging from 49 to 214µg/m3, in comparison to the WHO interim target-1 of 35µg/m3. Furthermore, a comparison of pollution levels in rural areas with those in Dhaka, one of South Asia's most polluted megacities, revealed that many rural sites exhibited comparable or within 10-20% of Dhaka's pollution levels. This finding suggests that regional pollution is a significant driver of PM2.5 pollution across the country, with local urban sources contributing an additional 10-20%. The study also identified a regional spatial gradient in measured pollution levels, with higher concentrations observed in the western and central parts of Bangladesh compared to the eastern region. This spatial gradient is likely due to the influence of transboundary pollution from neighboring Indian states, particularly the Indo-Gangetic Plain (IGP) states. The study's seasonal analysis demonstrated substantial variation in PM2.5 levels in rural areas. During the wet season, concentrations ranged from 49 to 98µg/m3, while during the dry season, they varied from 55 to 214µg/m3. These seasonal fluctuations are likely driven by meteorological factors, seasonal influx of transboundary air pollution, and seasonal sources. It is evident from the findings of the study that addressing PM2.5 pollution across Bangladesh requires a comprehensive, regional air quality management approach. Such an approach should encompass collaboration between various regions to collectively combat air pollution effectively and safeguard public health. While this study is a significant advancement in understanding PM2.5 pollution in Bangladesh, to gain deeper insights into long-term pollution dynamics, it is crucial to conduct multi-year continuous measurements in rural locations. Additionally, it is essential to characterize the long-term performance of low-cost sensors to ensure their sustainable and effective application in rural areas.