Air pollution is increasingly concerning for the environment and health in Africa, yet high-resolution, dependable data are limited. This study provides a comprehensive assessment of air quality in Kigali city, Rwanda's capital, using real-time PM2.5, NO2, and O3 measurements from 11 stations across three districts (Gasabo, Kicukiro, and Nyarugenge) spanning 2021 to 2024. All data were collected using a low-cost sensor (Real-time Affordable Multi-Pollutant (RAMP)) and validated with data from a reference-grade Beta Attenuation Mass Monitor (BAM). The results show that PM2.5 levels regularly exceed WHO guidelines across all seasons, with annual averages ranging from 33.6 to 46.3 & micro;g m-3 and peak episodes exceeding 200 & micro;g m-3, especially during dry months. NO2 levels ranged from 18.6 to 22.9 & micro;g m-3 annually, with the peak hourly concentration reaching 173 & micro;g m-3 at roadside locations. O3 displayed significant seasonal changes, with 8 hour maximums reaching nearly 58 ppb. PM2.5 and O3 concentrations at the urban roadside sites were significantly higher than those at the urban background and rural sites. This is the first comprehensive long-term citywide air quality study in Rwanda, providing an essential baseline for informed policymaking and regional comparisons across sub-Saharan Africa. Our findings highlight the need to expand the deployment of low-cost sensor networks in vulnerable urban neighbourhoods to understand local-scale air pollution episodes and rapidly inform local interventions.

The first multi-year, citywide study in Rwanda found that pollutant levels vary by land-use type and that low-cost sensors can reliably fill air-quality data gap in Africa.

Multiple particulate matter (PM) metrics can be analyzed using the same filter samples. Splitting samples for archival and multidisciplinary purposes is essential for a more health-relevant metric analysis. However, there is little information on minimum masses to determine aerosols, or how sampling duration and the fraction of filter used influence the concentrations of polycyclic aromatic hydrocarbons (PAHs) and their nitro-derivatives (NPAHs). This study evaluated the influence of sampling duration (24 h, 5 d, 7 d) and filter extraction fraction (1/2, 1/4, 1/8 of the filter area) on PAH and NPAH quantification in fine and coarse particulates collected using a high-volume air sampler in Auckland, New Zealand. Samples were analyzed for 14 PAHs and 9 NPAHs using high-performance liquid chromatography. Concentrations normalized to sampled air volume (pg m-3) were consistently highest in 24 h samples and decreased substantially during multi-day sampling. Filter area fraction bias increased with sampling duration and decreased with extraction area, with 1/8 fractions showing the largest deviations from the half-filter references, particularly at extended durations, while quarter fractions remained closer to the half-filter reference. Stacked-fraction analysis indicated that small punches may not adequately represent full-filter composition during extended sampling periods. Both low- and high-molecular-weight compounds exhibited sensitivity to sampling duration. Diagnostic ratios and principal component analysis indicated compositional shifts and potential secondary formation of NPAHs during multi-day sampling. The amount of particulates collected during 24 h sampling was sufficient for analyzing PAHs and NPAHs, but required a larger sampling area (at least half of the whole filter) to reflect the entire filter. Extended sampling and small filter punches introduced greater heterogeneity and analytical bias. Shorter collection periods did not come at the cost of concentrations and may enable several consecutive monitoring samples. These findings provide practical guidance for optimizing filter-based monitoring of PAHs and NPAHs in atmospheric PM.

Background. Diarrhoeal disease remains a leading cause of morbidity and mortality among children under five years (U5) in Rwanda, contributing substantially to healthcare utilisation and imposing considerable economic burdens on households and the health system. National estimates indicate that approximately 14.3% of children under five experienced diarrhoea in the two weeks preceding the 2019–2020 Rwanda Demographic and Health Survey, and diarrhoea has been reported as the third leading cause of death in this age group. Climate variability may influence the risk of diarrhoeal disease, but evidence on how specific climatic factors affect diarrhoeal incidence across Rwanda’s diverse ecological zones and seasons remains limited. This study examined associations between maximum temperature, minimum temperature, rainfall, and relative humidity and U5 diarrhoeal incidence at the sector level in Rwanda. Methods. Monthly counts of U5 diarrhoeal cases reported by health facilities across 416 administrative sectors in Rwanda from January 2015 to December 2024 were analysed together with satellite-derived climate data. Spatio-temporal statistical models were used to evaluate associations between standardised climate variables and diarrhoeal incidence rates while accounting for geographic and seasonal variation. Model comparison relied on both goodness-of-fit metrics and out-of-sample predictive diagnostics. Results. Diarrhoeal incidence showed clear spatial and seasonal patterns, with persistently higher rates in northern and eastern Rwanda. In the final model maximum temperature was positively associated with increased diarrhoeal incidence, with a one-standard-deviation increase corresponding to a 5.6% rise in the estimated incidence rate ratio (RR = 1.056; 95% CrI: 1.02–1.09). Relative humidity showed a protective association (RR ≈ 0.919; 95% CrI: 0.89–0.94), while rainfall showed limited immediate effects. Conclusion. Under-five diarrhoeal incidence in Rwanda showed marked spatial and seasonal variability. Maximum temperature was positively associated with diarrhoeal incidence rates, while relative humidity showed an inverse association that may partly reflect unmeasured confounding by drought, water access, and WASH infrastructure. External validation is needed before the modelling framework can be applied operationally. These findings highlight the importance of preparedness during hotter periods and strengthened prevention and surveillance efforts in high-risk areas.

IntroductionCar-Free Days (CFDs) in Kigali, Rwanda, are held twice monthly on Sundays, when motorized vehicle traffic is restricted on major roads from 7:00 AM–11:00 AM to promote physical activity and reduce air pollution. Previous studies assessing the effectiveness of CFDs in reducing air pollution in Kigali have relied solely on short-term, low-cost fine particulate matter (PM2.5) measurements during the intervention period at a single site and have provided no post-intervention rebound assessment. The present study provides the first record of variations in PM2.5 and ozone (O3) to evaluate the effectiveness of CFDs as a sustainable transport emission-reduction strategy. We examine whether reductions in air pollution persist beyond implementation hours and contribute to overall daily improvements in air quality in Rwanda.MethodsContinuous air quality data collected between 2022 and 2024 from two sites were analyzed. Pollutant concentrations during CFD Sundays were compared to normal Sundays across morning intervention (7:00 AM–11:00 AM) and post-intervention (11:00 AM–9:00 PM) periods.Results and discussionResults show that PM2.5 concentrations significantly decreased during CFD hours (−14.8%, P < 0.0001) and remained lower in the post-intervention period (−34.7%; P < 0.0001), with no evidence of rebound. Diurnal profiles showed continued declines after 11:00 a.m. and a suppressed evening peak, indicating a sustained reduction in daily exposure. In contrast, O3 showed no significant differences during CFD hours and increased in the afternoon, consistent with photochemical formation rather than direct traffic emissions. This study highlights that CFDs may serve as an effective, low-cost, and sustainable strategy to reduce transport emissions in Africa, where expensive interventions to reduce air pollution are lacking. These findings also highlight the potential of community-based interventions to enhance urban environmental sustainability and resilience, especially in rapidly urbanizing cities.

Environmental noise pollution is an underestimated problem, despite its proven effects on public health in rapidly urbanizing cities, particularly in sub-Saharan Africa, where empirical data remains limited. This study aims to analyze the spatial and temporal variability of environmental noise pollution in Bukavu, Democratic Republic of the Congo (DRC), a city characterized by rapid population growth, a high concentration of schools, and a high intensity of urban activity. Noise levels (LAeq) were measured using an SPL-25 sound level meter at 17 specific sites, categorized based on three land use types, including commercial, residential and schools, spanning the wet and dry seasons, during the daytime (07:00–18:00). Descriptive statistical analyses and seasonal comparisons were carried out, supplemented by spatial interpolation (IDW) to map the distribution of noise. Average noise levels in the wet season (67.83 ± 9.36 dB(A)) and the dry season (66.81 ± 8.55 dB(A)) were above the World Health Organization's daytime noise threshold. Maximum recorded levels reached 114.0 dB(A) in commercial areas and 111.3 dB(A) in school zones, exposing schoolchildren to worrying levels of noise pollution. Spatial analysis using GIS revealed a heterogeneous distribution of noise (30.8-114 dB(A)) with hotspots along the roads of Bukavu. Noise levels were high during the day and in the evening, with noise peaks more noticeable in the morning and evening at sites with heavy traffic. These findings underscore the need to incorporate noise management into urban planning and environmental health policies to reduce urban population exposure.

Air pollution poses a severe public health challenge in Africa, where ambient particulate matter (PM) concentrations often far exceed World Health Organization (WHO) guidelines. Children are particularly vulnerable, spending long hours in poorly ventilated classrooms, which are often poorly constructed and designed, and inadequately maintained, and where indoor air quality (IAQ) is rarely monitored or improved. This study provides one of the first experimental evaluations of air purifiers (APs) in an African school environment in Rwanda. Minute-level measurements of PM1, PM2.5, and PM10 were collected under two conditions (with and without AP operation) and classified into learning hours (LH) and non-learning hours (non-LH). Wilcoxon rank-sum tests and rank-biserial correlations were used to assess the effects of APs. AP use significantly lowered mean PM concentrations throughout the day (5.16% for PM1, 12.27% for PM2.5, 11.58% for PM10). The amplification of the diurnal PM decline by APs during learning hours led to substantial reductions (29.79% for PM1, 33.12% for PM2.5, and 34.31% for PM10), with significantly larger effect sizes compared to the no-AP condition. APs also accelerated PM2.5 and PM10 declines to below WHO Interim Target-1 (IT-1) thresholds (35 μg/m3 and 70 μg/m3) within 1.96 and 1.26 hours, respectively. These findings provide robust evidence that APs can rapidly and effectively improve IAQ in African schools, offering a feasible intervention to safeguard schoolchildren’s health and support healthier learning environments.

Airborne microbes significantly influence environmental processes and human exposure, yet they remain poorly characterized in Africa. This study presents a regional survey of airborne bacterial and fungal communities across 10 sites in five East African countries: Burundi, the Democratic Republic of the Congo, Kenya, Rwanda, and Tanzania. Polyurethane foam passive air samplers (PUF-PASs) were deployed concurrently, and airborne bacterial and fungal communities were characterized using 16S rRNA gene and ITS amplicon sequencing. Genus-level analyses identified both bacterial taxa (Massilia, Sphingomonas, Pseudomonas, Bacillus, and Kocuria) and fungal genera (Cladosporium, Alternaria, Aspergillus, Curvularia, and Penicillium) that are commonly detected in outdoor air and urban atmospheric environments. Beta-diversity analysis revealed no significant country-level differences in bacterial communities (ANOSIM (R = -0.045, p = 0.597)), while fungal communities exhibited significant differences among countries (ANOSIM (R = 0.652, p = 0.002)). Cross-border comparisons showed that nearby sites within 10 km did not consistently share similar microbial profiles. These findings indicate a broadly shared regional bacterial aerobiome, with more pronounced spatial structuring among fungal communities. This study serves as a proof-of-concept demonstration that PUF-PASs can be used to characterize airborne microbial communities in East Africa, while highlighting the need for future bioaerosol research with enhanced temporal replication and broader spatial coverage to support long-term public health surveillance in the African region.

Exposure to particulate matter (PM) is a major global health concern, yet the potential relationships between its chemical and microbial components remains poorly understood, particularly in rapidly urbanizing, understudied settings. This study presents an integrated assessment of polycyclic aromatic hydrocarbons (PAHs), nitrated PAHs (NPAHs), bacteria, and fungi in both fine (PM2.5) and coarse (PM10) aerosols across urban, roadside, and rural sites in sub-Saharan Africa, with a focus on Rwanda across dry and wet seasons. Microbial analysis revealed that the richness and community structure of the airborne bacterial and fungal communities varied with land-use type, linked with PAH/NPAH abundance, PM size fraction, and season. Spearman correlation coefficient confirmed that bacterial communities were more strongly associated with PAH and NPAH compounds, whereas fungal communities were shaped primarily by environmental factors. One bacterial genus, Sphingobium, exhibited evidence of selective enrichment within the PAH rich PM2.5 size fraction, highlighting the potential for direct interaction between the biological and chemical compositions in air. We provide a critical baseline for African cities where air quality data are scarce. Current air quality standards, which prioritize chemical thresholds, overlook the biological burden carried by PM.

We present the first comprehensive comparison of polyurethane foam disk passive air samplers (PUF-PASs) and active high-volume air samplers (Hi-Vol) for bioaerosol monitoring in side-by-side deployments. Using qPCR, 16S rRNA gene sequencing, and multivariate analysis, we demonstrated that the PUF-PASs detected higher bacterial biomass, as evidenced by significantly elevated gene copy numbers and estimated bacterial cells per m3 of air volume, but exhibited lower diversity compared to Hi-Vol samplers. Hi-Vol samplers recovered a more taxonomically diverse community, including transient and rare taxa, during sampling periods of 1 day and 1 week. Hi-Vol detected genera not detected in long-term PUF-PAS sampling, while PUF-PAS detected species not observed in short-term Hi-Vol. PUF-PAS samples were enriched with environmental and spore-forming persistent genera. Hi-Vol samples were enriched with opportunistic and human-associated episodic spikes in a range of bacterial species. PCoA analysis confirmed a substantial divergence in bacterial community structure by sampler type and duration. Temporal analysis results showed a progressive shift in bacterial community composition with increasing sampling duration in PUF-PAS. The findings highlight the complementary benefits of both sampler types: active air sampling for capturing short-lived human-associated bioaerosols and taxonomic richness, while passive air samplers favor biomass accumulation and chronic exposure profiling, enabling exposure assessment and ecological surveillance.

Household air pollution (HAP) contributes to the global cardiovascular disease burden. Early life exposures may impact future disease risk; however, evidence of HAP's impact on blood pressure (BP) among children in low-resource settings is limited. We assessed baseline cross-sectional associations between personal exposure to fine particulate matter (PM2.5) and black carbon (BC) and children's (8-15 years) systolic and diastolic BP (SBP, DBP) from the Sustainable Household Energy Adoption in Rwanda study. We enrolled 626 households in rural Eastern Rwanda that used traditional biomass fuels for cooking. Children wore Ultrasonic Personal Aerosol Samplers for 48 h monitoring of personal exposure, followed by BP measurement using standard protocols. Multiple linear regression was used to characterize associations between PM2.5 and BC exposure and BP in separate models; effect modification by age and sex was evaluated. Among 622 children (mean age = 11.8 years, standard deviation [SD] = 2.1; males = 303, females = 319), the average SBP and DBP were 105.8 mmHg (SD = 10.0) and 68.3 mmHg (SD = 7.6), respectively. BP percentiles were higher than those in a US reference population (e.g. 59.0% and 85.5% had SBP and DBP percentiles >50th, respectively; 24% were classified as having elevated BP and/or were hypertensive, defined as ⩾90th percentile). The median 48 h PM2.5 and BC concentrations were 192.9 µg m-3 (25th percentile [Q1] = 119.7, 75th percentile [Q3] = 336.0) and 9.85 µg m-3 (Q1 = 6.56, Q3 = 13.23), respectively. We did not observe evidence of associations between HAP and BP levels (e.g. PM2.5-SBP = 0.51 mmHg per interquartile range [IQR, 211.7 μg m-3] increase, 95% confidence interval: -0.46, 1.49). We did not observe clear evidence of effect modification. Exposures well above international health-based guidelines may have limited our ability to observe associations if the true exposure-response is flat in that part of the global exposure continuum. Importantly, our BP data suggest an elevated cardiovascular disease burden among children in this low-resource setting compared to in the US, demonstrating a need for more research and the development of more appropriate reference data in these settings. ClinicalTrials.gov Identifier: NCT05668624.

Fine particulate matter (PM2.5) and black carbon (BC) are major air pollutants with impacts on human health and regional climate, yet very little information on spatiotemporal distributions in African cities currently exists. This study analysed spatiotemporal variations in the concentration of PM2.5 and BC in African urban and rural areas, with special attention to Kigali, in Rwanda. The data revealed average values for PM2.5 of 22 to 38 mu g m(-3), well above the WHO recommended thresholds, with higher values recorded in the dry season. The average concentration level of BC was 13.4 +/- 9.7 mu g m(-3) in urban areas and 7.7 +/- 4.4 mu g m(-3) in rural areas, demonstrating strong seasonal variation and with morning and evening peaks reflective of traffic density and household fuel usage, respectively. Source identification showed fossil fuels contributed approximately 60% of the total BC at urban sites. These findings highlight the growing influence of urbanization and transport emissions in Rwandan cities and emphasize the importance of continuous air quality monitoring to guide mitigation strategies.

Accurately predicting air quality is a crucial challenge for public health and environmental management. This study compares and contrasts machine learning approaches to benchmark best practices for the Rwandan context and to evaluate the added value of advanced statistical methods for air quality monitoring in data-scarce settings. We forecast fine particulate matter (PM2.5) concentrations across five provinces in Rwanda, using multi-year meteorological and air quality data to identify context-specific patterns. This work establishes a methodological foundation for context-optimized early warning systems and informs policy interventions to improve air quality management in Rwanda. By rigorously testing machine learning capabilities against regional constraints, we demonstrate how machine learning can reduce population exposure to pollution, quantify attribution gaps in under-monitored regions, and improve sustainable environmental governance in resource-limited settings. The results indicate significant seasonal variability, with higher PM2.5 levels during dry seasons than wet seasons. Our evaluation demonstrates that machine learning models can capture complex, non-linear relationships between environmental variables and pollution trends, although performance varies between algorithms. Limitations remain, including the integration of real-time data streams and localized variables such as industrial emissions, road traffic, and agricultural practices.

Mounting evidence demonstrates that heatwaves aggravate urban air pollution, with substantial impacts on public health, but comparatively little research has addressed Sub-Saharan African contexts. In this study, we focused on Kigali, Rwanda, to assess the relationship between extreme heat events and concentrations of fine particulate matter (PM2.5), nitrogen dioxide (NO2), and ozone (O3) from 2021 to 2024. Using low-cost sensors for dense spatiotemporal coverage, our analysis finds that O3 concentrations increased significantly during 6 heatwave events with peak values up to 40% higher during heatwaves. Heatwaves also resulted in spikes in PM2.5 and NO2, however the diurnal and seasonal analyses showed that PM2.5 and NO2 dynamics were shaped more by local emissions than temperature alone. These results highlight the compound risks of heat and air pollution in sub-Saharan African cities, underscoring the importance of early-warning systems and robust urban policies that account for both heat and air pollution. In addition, the atmospheric dynamics identified in this research differ from those observed in many high-income countries, highlighting a critical need for more research exploring the intersection of heat and air pollution in Sub-Saharan Africa.

Lead (Pb) and cadmium (Cd) are metals that occur naturally in the environment and are present in biomass fuels, such as wood. When these fuels are burned, they can release Pb and Cd into the air, leading to exposure through inhalation. Studies of exposure to metals and health outcomes suggest harmful impacts, including cardiovascular diseases. We assessed baseline associations between Pb and Cd concentrations in dried blood spots with systolic and diastolic blood pressure (SBP, DBP) among women in the Household Air Pollution Intervention Network (HAPIN) trial. We analyzed data from three of the four HAPIN randomized controlled trial sites (Guatemala, Peru, and Rwanda), focusing on women aged 40 to 79 years living in households reliant on biomass cooking. Dried blood spots were collected, processed, and analyzed for Pb and Cd exposure; SBP and DBP were measured following international guidelines. Demographic, socioeconomic, and dietary variables were collected via standardized questionnaires administered by local field staff. Statistical analyses included multivariable linear regression to examine associations between Pb and Cd, separately, and BP, adjusting for covariates informed by a Directed Acyclic Graph. Additional analyses assessed effect modification by age and research site. There was regional variation in BP levels among women, with median SBP and DBP values higher in Rwanda (116.3 mmHg, 73.0 mmHg) and Guatemala (113.3 mmHg, 68.3 mmHg) compared to Peru (106.0 mmHg, 63.3 mmHg). Pb exposure showed positive associations with both SBP and DBP. For each log-unit increase in Pb concentration, we observed increases of 2.36 mmHg SBP (95% CI 0.51, 4.20) and 1.42 mmHg DBP (95% CI 0.16, 2.67). Cd was not associated with SBP or DBP in this analysis. Pb exposure may be an important risk factor for increased SBP and DBP, markers of cardiovascular disease risk.

Indoor air pollution presents a significant global health risk, yet the influence of outdoor air pollution and meteorological factors on indoor air quality is not well understood. This study investigates these impacts in 88 naturally ventilated households across urban, suburban, and industrial areas, with no indoor smoking or cooking. Air quality measurements were continuously recorded for 24 h a day over six consecutive days during the wet season. The findings reveal that the outdoor PM2.5 levels consistently exceeded indoor levels, with weekday concentrations higher than on weekends. Specifically, urban PM2.5 levels averaged 34.8 μg/m³ outdoors and 31 μg/m³ indoors on weekdays, compared to 33.1 μg/m³ outdoors and 31.5 μg/m³ indoors on weekends. Indoor CO2 levels were notably higher, peaking at 525.7 ppm in urban areas on weekdays and 576.9 ppm on weekends, driven by increased occupancy and poor ventilation, particularly in suburban areas (880.4 ppm on weekdays and 807.5 ppm on weekends). The average indoor/outdoor (I/O) ratio for PM2.5 was 0.94, indicating that indoor concentrations are about 94% of outdoor levels, signifying significant infiltration of outdoor pollution. In contrast, the I/O ratio for CO2 was 1.47, suggesting indoor levels were 47% higher due to limited ventilation and indoor sources. This study concludes that outdoor air pollution and meteorological factors significantly affect indoor air quality in Kigali, Rwanda, highlighting the need for effective management of both outdoor pollution sources and indoor conditions.

A lack of long-term air quality monitoring data in African countries such as Rwanda poses a significant challenge as urbanization leads to declining air quality. This study uses four years of data on particulate matter air pollution (PM2.5) to understand the current drivers of air pollution, the success of current interventions and the potential for further actions. PM2.5 data were collected using low-cost and reference monitors in two sites in Kigali. Results show that PM2.5 levels in Kigali exceeded the recommended WHO air quality guidelines. Using the COVID-19 lockdown as a natural experiment, we find that reduced travel activity of over 80% led to PM2.5 levels declining by 33%, suggesting that transport may account for a smaller share of particulate emissions than is assumed in government literature. We also find that a program to encourage non-motorized transport in Kigali called 'Car-Free Days' reduced by PM2.5 15% when it was held between 2017 and 2020. This reduction is expected to have resulted in more than 200 disability-adjusted life years saved in Kigali annually, about 150 hospital visits, and 600 lost working days being avoided. We conclude by reflecting on the policies for improving air quality in Kigali City.

Africa has the world's youngest population, with 40 % aged between 0 and 15 years, and it remains the region most affected by air pollution. In many African cities, kindergarten schools are often located in high-density and polluted urban environments with high levels of hazardous pollutants, including atmospheric polycyclic aromatic hydrocarbons (PAHs). Compared to the rest of the world, limited studies have quantified the exposure to and associated health risks of PAHs in schools in Africa. This study first characterizes and identifies sources of atmospheric PAH and assesses the health risks at a kindergarten school in Rwanda. Fine particulate matter (PM2.5) was collected during the dry and wet seasons using a mini-volume air sampler, and 16 PAHs were characterized using gas chromatography. The total mean concentration of 16 PAHs was higher in the dry season (52.7 +/- 21.9 ng/m(3)) than in the wet season (49.5 +/- 14.7 ng/m(3)) and exceeded the levels reported in kindergarten schools in high-income countries. Source analysis using PAH diagnostic ratios and correlation analysis of PAHs with black carbon from biomass burning and fossil fuel showed that wood burning for cooking fuel and diesel traffic emissions were the main sources of PAHs at the kindergarten school. The estimated cancer risk level significantly exceeded the World Health Organization's safe limit and indicates that children at kindergarten in Rwanda are exposed to high levels of toxic PAHs. Immediate attention is required, and schools should consider implementing policies and interventions to reduce children's exposure to air pollution at kindergarten schools.

Indoor air pollution is a growing concern as people spend most of their time indoors. However, information on indoor air quality and factors influencing indoor exposures remains limited, particularly in rapidly urbanizing cities like Kigali, Rwanda. To address this gap, this study examined the distribution of carbon monoxide (CO) levels and fine particulate matter (PM2.5) in residential and commercial buildings. Indoor and outdoor PM2.5 and CO concentrations. Along with meteorological variables such as relative humidity (RH) and temperature, were measured every two minutes over 24-h period during both dry and wet seasons. PM2.5 measurements were conducted from March to August 2024 in residential and commercial buildings, CO measurements were conducted from June to August 2024 in 88 households across urban, suburban, and industrial zones. The study found significantly higher PM2.5 levels during the dry season, with indoor levels averaging 40.2 ± 19.3 μg/m3 and outdoor levels 41.3 ± 17.5 μg/m3, compared to the wet season, where indoor levels were 32.8 ± 82.9 μg/m3 and outdoor levels 35 ± 15.8 μg/m3 outdoors. CO levels were consistently higher outdoors (691.3 ± 181.8 μg/m3) than indoors (478.4 ± 128.2 μg/m3). Indoor/outdoor (I/O) ratios for PM2.5 were consistently below 1, indicating a strong influence of outdoor sources on indoor PM2.5 levels. While, location type showed a slight correlation with PM2.5 concentrations, building features such as age, window count, and ventilation exhibited varying but insignificant impacts. These findings highlight the critical role of outdoor pollution and meteorological factors in determining indoor air quality in Kigali and underscores the need for regulating outdoor pollution sources and indoor environments.