The Linkages between Air Quality Index, Environmental Quality and Self- Reported Respiratory Conditions. Empirical Evidence from Selected Industrial Locations in Lagos State, Nigeria

Technical Summary: The Linkages between Air Quality Index, Environmental Quality and Self-Reported Respiratory Conditions in Lagos State, Nigeria

Problem Statement
Ambient air pollution (AAP) is a critical global health challenge, responsible for over 3 million annual deaths, with disproportionate impacts on developing nations. In Nigeria, particularly Lagos State—the country's most industrialized and populous region—air pollution studies have historically focused on diurnal and seasonal variations of gaseous and particulate pollutants. However, there is a notable gap in research regarding the nexus between air pollution, soil quality, rainwater pH, and self-reported respiratory conditions within active industrial estates. This study addresses this gap by investigating the environmental quality and health outcomes in five selected industrial locations in Lagos, aiming to quantify the linkages between the Air Quality Index (AQI), soil contamination, and respiratory morbidity.

Methodology
The study employed a mixed-methods approach combining field monitoring, laboratory analysis, and survey research across five active industrial estates (Ikeja/Ogba, Surulere, Odogunyan, Apapa, and Oshodi/Ilupeju) and one control site (Alausa).

• Air Quality Monitoring: Primary data were collected over 12 months (February 2020 to May 2021). Using standard measuring devices (Teflon filters, VRAE multi-detectors, and Tecto 315-2 detectors), the study monitored four key pollutants: Sulfur Dioxide (SO2), Nitrogen Dioxide (NO2), Carbon Monoxide (CO), and Fine Particulate Matter (PM2.5). Sampling occurred for eight hours monthly at 10 points per location.
• AQI Computation: The United States Environmental Protection Agency (USEPA) Air Quality Index was utilized to calculate and categorize pollution levels based on the measured concentrations.
• Environmental Sampling:
  • Soil: 12 soil samples (2kg each) were collected from Odogunyan and Ikeja/Ogba estates and the control site in July 2021. Analysis was conducted to detect elemental composition. The abstract explicitly states that soils were contaminated with Cadmium, Lead, and Arsenic compared to the control site, while the results section figures and text highlight high concentrations of Chromium, Lead, and Nickel.
  • Rainwater: Six rainwater samples were collected during the wet season (July–October 2021) and analyzed via titrimetric analysis for pH levels.
• Health Data:
  • Self-Reported: A modified British Medical Research Council Questionnaire was administered to 1,067 respondents to capture self-reported respiratory symptoms and morbidities.
  • Hospital Data: Respiratory condition data were sourced from general and teaching hospitals in the study area for a 12-month period.
• Statistical Analysis: Multiple linear regression was used to test the relationship between monthly AQI values and hospital-based respiratory conditions.

Key Results

• Air Quality Index (AQI) Variations:

  • Seasonality: AQI values were consistently higher during the dry season compared to the wet season across all locations, attributed to the lack of precipitation scavenging.
  • Dry Season: Odogunyan recorded "Very Unhealthy" AQI levels (229 ± 33.73). Surulere, Oshodi/Ilupeju, Apapa, and Ikeja/Ogba were classified as "Unhealthy for Sensitive Groups" (ranging from 119 to 130). The control site, Alausa, remained "Moderate" (64 ± 18.40).
  • Wet Season: Odogunyan remained "Unhealthy" (161 ± 51.19). Surulere and Oshodi/Ilupeju were "Unhealthy for Sensitive Groups," while Apapa, Ikeja/Ogba, and Alausa improved to "Moderate."
  • Pollutant Drivers: PM2.5 levels were highest in Odogunyan and Surulere due to industrial emissions and traffic. SO2 levels were elevated in Odogunyan and Apapa, linked to furnace oil usage. NO2 was high in Apapa and Odogunyan due to traffic volume.

• Soil and Rainwater Quality:

  • Soil Contamination: The study presents conflicting findings regarding specific heavy metals. The abstract reports that soils in industrial locations were contaminated with Cadmium, Lead, and Arsenic relative to the control site. However, the results section (Figures 19 and 20) and discussion highlight high concentrations of Chromium, Lead, and Nickel in the industrial estates compared to the control.
  • Rainwater pH: Rainwater pH ranged from 5.7 to 6.9, which is within the normal range (5.6–6.5) and indicates no significant acid rain (pH < 4.4) or acidification of the atmosphere by industrial emissions in the study area.
  • Soil pH: Soil pH in the industrial areas was alkaline (7.1–8.64), suggesting that factors other than rainwater acidification (e.g., geology, vegetation, fertilizers) determine soil pH in these locations.

• Health Outcomes and Regression Analysis:

  • Symptoms: The most frequently self-reported symptoms included coughing, headache, cold/catarrh, eye irritation, and tiredness. Major morbidities reported were asthma and pneumonia. Odogunyan, Surulere, and Apapa reported the highest incidence of respiratory disorders.
  • Regression Findings: The model explained 43% of the variation in monthly hospital-based respiratory conditions (R² = 0.430).
    • PM2.5 AQI: Significantly increased respiratory conditions by 35.1% (β = 1.351, p = 0.000).
    • NO2 AQI: Significantly reduced reported conditions by 2.8% (β = -2.028, p = 0.003), a counter-intuitive result noted in the paper.
    • SO2 and CO AQI: Did not show a statistically significant influence on monthly hospital visits.
  • Demographic Factors: Gender, occupation, housing type, and cigarette smoking were identified as significant influencers of respiratory symptoms.

Key Contributions
The paper provides empirical evidence linking specific industrial locations in Lagos to degraded air quality and adverse health outcomes. Its primary contributions include:

1. Spatial and Temporal Mapping: Detailed characterization of AQI variations across five major industrial estates in Lagos, distinguishing between wet and dry season impacts.
2. Multi-Environmental Assessment: Simultaneous evaluation of air, soil, and rainwater quality, revealing that while air quality is severely compromised in specific zones (notably Odogunyan), rainwater acidification is not currently a primary issue, though soil heavy metal contamination is significant (with noted discrepancies in the specific metals identified between the abstract and results).
3. Health Correlation: Establishing a statistical link between PM2.5 levels and hospital-based respiratory conditions, highlighting PM2.5 as a critical driver of morbidity in these industrial zones.

Significance and Claims
The authors assert that industrial ambient air pollution is a single biggest threat to environmental and human health in Lagos, particularly during the dry season. The study claims that the findings:

• Validate the Need for Intervention: The poor air quality in industrial estates negatively impacts the quality of life and health of residents and workers, necessitating urgent policy action.
• Support Sustainable Development Goals (SDGs): The outcomes inform policymakers on the necessity of achieving SDG 9 (Industry, Innovation, and Infrastructure) and SDG 11 (Sustainable Cities and Communities) by building resilient infrastructure and promoting sustainable industrialization.
• Propose Practical Solutions: The paper advocates for the adoption of real-time monitoring technologies (e.g., Air Beam sensors), citizen science engagement, increased green spaces for bio-filtration, improved road infrastructure to reduce dust, and a transition to cleaner fuels and renewable energy sources (biofuels, solar) to reduce reliance on fossil fuels.

The study concludes that while the rainwater pH remains benign, the accumulation of toxic elements in soil and the high AQI levels in dry seasons pose a direct threat to public health, requiring a multidisciplinary approach involving government, industry, and the public to mitigate risks.