A seasonal investigation of indoor air quality in relation to architectural features in government office buildings in Enugu, Nigeria

The study area is the Enugu metropolis, one of the major cities in the region, located in the state of south-eastern Nigeria (Fig. 1). It is located on the eastern periphery of Udi Cliff and lies between latitude 6.4610 N and longitude 7.4940E within the tropical hot-humid region of Nigeria. The discovery of coal mining in 1909 by engineer Mr. Kitson led to the establishment of a railway line from Port Harcourt through Enugu for coal export, attracting migrants and leading to planned construction for coal miners and civil servants. Enugu gained township status in 1917 under Lord Lugard’s Ordinance and has been the capital of Enugu State since its creation in 1991. Enugu’s topography is undulating with hills, and it is situated 200 m above sea level, part of the Nsukka-Udi-Okigwe Cuesta. The city experiences conventional and disturbance-related rainfall, with an annual mean ranging from 1500 mm to 1750 mm^22,23.

Map of Enugu metropolis²⁴.

The research focuses on the Enugu metropolis, which houses approximately 50 government parastatals, including 23 state government and 27 federal government parastatals. The study population includes offices from all three government tiers: Federal, State, and Local Government, all within the metropolis. Each secretariat building has unique features but shares similarities within its category.

The research design utilised in this study involved a case study approach, focusing on multiple sites and incorporating both experimental and survey research designs. This decision was driven by the necessity to comprehensively ascertain the concentration/level of the main indoor air quality (IAQ) parameters within office buildings during rainy and dry seasons (the two major seasons in the region). Additionally, it aimed to enhance understanding regarding the relationship between the architectural characteristics of office buildings and the seasonal variations in IAQ parameters. Furthermore, the study sought to explore how architectural features may impact seasonal IAQ in office buildings in the hot and humid tropics of Enugu, southeast Nigeria.

Specific criteria were established to determine the sample size of the offices by examining various office types/ layouts, including private offices, open-plan offices, and traditional/ cubicles office. Factors such as their cardinal directions (North, South, East, or West) and their position within the office complex (ground floor or suspended floor) were also considered. These criteria allowed for classifying office types into distinct models, each sharing similarities with others in its category. Furthermore, additional selection determinants included office surface area, and counts of furniture, headroom (floor to ceiling height), window characteristics (types, sizes, and numbers), occupant numbers, floor/wall/ceiling finishes, surrounding landscapes, presence of electronic devices, and other architectural features.

Following these selection guidelines, a sample size of 58 offices was identified for the study. This comprised 24 offices from the Federal Government secretariat complex, 24 from the Enugu State Government secretariat complex, and 10 from the Enugu North Local Government secretariat complex. This approach ensured a well-balanced representation of various office buildings with varying characteristics within the designated research area.

The BOSEAN Multi-function office/home air Quality detector, model T-Z01Pro, an 8-in-1 Air Quality Detector²⁵. It was employed to assess the office Indoor Air Quality parameters of interest. Chosen for its comprehensive capabilities, this device has four sensors that concurrently measure PM2.5, HCHO, TVOC, CO, and CO₂ concentrations in the air, along with detecting temperature, humidity, and the Air Quality Index (AQI). The detector offers precise measurement accuracy and ranges of 0–1.999 mg/m3 for HCHO, 0–9.999 mg/m3 for TVOC, and 0–999 µg/m3 for PM2.5, ensuring both efficiency and accuracy.

Also, a carefully prepared observation schedule was developed to facilitate the comprehensive field survey and capture detailed information regarding all investigated office buildings’ architectural features, occupancy, furnishing details, and surrounding attributes. Each office was systematically coded on the observation schedule in relation to the office complex design floor plans to ensure ease of identification and location. The coding system employed a combination of cardinal point orientation (A for north, B for east, C for west, and D for south), office layout type (1 for private office, 2 for open plan office, and 3 for traditional/ cubicle office), and location within the building complex (1 for ground floor and 2 for suspended floor), with layout and location denoted as subscripts for clarity and precision.

The study employed a combination of qualitative and quantitative research approaches. For the qualitative research, a well-articulated observation schedule was used to identify the architectural design features of the selected office buildings. For quantitative analysis, which constitutes an experimental approach, the BOSEAN Multi-function office/home air quality detector, model T-Z01Pro, an 8-in-1 Air Detector, was employed to evaluate the concentration/level of the Indoor Air Quality parameters under investigation. The instrument was calibrated using manufacturer’s recommended procedures on the operation manual. This involved placing the machine in clear air, running it for 15 min with an unobstructed air vent, and selecting “set” on the device to initiate automatic calibration²⁵. To ensure precise measurements, the detector was strategically positioned at the centre of the office floor, away from aisles, to minimize disruption from daily office activities. To replicate the breathing zone of a seated office worker, the monitor was positioned 1 m above the floor on a desk. Data were collected at 15-minute intervals in real-time, commencing from 8 am (the start of the workday) to 4 pm (the end of the workday), and their averages were calculated. The data collection period spanned four consecutive days per office, from Tuesday to Friday, both in the rainy (May to August) and dry seasons (November to December). Measurements were taken in 57 offices out of the sample size of 58 offices.

The experimental design aimed for the field survey to encompass a range of indoor climatic conditions, stretching across the two major seasons in Nigeria (Rainy and Dry Seasons). The survey’s structure was calculatedly crafted to facilitate daily record-keeping, fostering a precise and comprehensive assessment of the indoor air quality of the case study office buildings. To ensure thoroughness, each office was surveyed on at least four occasions per season.

The Statistical Program for Social Sciences 23 was used to evaluate measurement data statistically. Mean and standard deviation values were calculated using this program. Additionally, the paired T-test was used to determine the seasonal variations and significance of the IAQ parameters. Finally, analysis of variance (ANOVA) was used to determine the statistically significant relationship between the variables and the architectural features of the three different study locations as it relates to seasonal changes.