Abstract

Globally, urban cities are mostly faced with poor air quality. About 4.2 million people die annually due to the exposure to air pollution. This study, therefore, aim to ascertain the environmental safety of an urban city of Port Harcourt by evaluating the air quality index (AQI) of some air parameters. The study involved a descriptive and evaluative analysis of air quality data of eleven stations within Port Harcourt metropolis from May to December 2020. The AQI calculation was performed using EXCEL Microsoft, and the result was classified using USEPA guidelines. The results showed that the highest average monthly concentration of CO₂ and NO₂ was reported in May. SO₂ and PM_2.5 was reported highest in August and October 2020 respectively. Furthermore, CO₂ AQI values in Port Harcourt were observed good throughout the study period (AQI<50), except in November that was observed moderate quality (AQI=58.56). NO₂ AQI values were good (AQI<50) in August, October, and November, while in May, September, and December moderate air quality was observed (AQI is between 71.56 and 85.53). AQI values for SO₂ were above 100, depicting unhealth and hazardous for human habitation. PM_2.5 only in May and October had good air quality (AQI <50), while in the other months were classified moderate (AQI = 74.60-90.50). We conclude that the AQI values indicates that the air quality was good or moderate with respect to CO₂ and NO₂, unhealthy with respect to SO_2, and moderate for PM_2.5 especially at stations with high human activities during the study period. To make the city safer, we recommended that human activities such as open-air combustion of refuse and artisanal refining of crude petroleum should be monitored regularly to check its impact on the air quality.

1. Introduction

World Health Organisation (WHO) define air pollution as the contamination of the environment by any chemical, physical or biological agent that alters the natural characteristics of the atmosphere ¹. Air quality is a measure of the concentrations of pollutants in the atmosphere. When damaged, it impacts negatively on the economies, natural system, and productivity of labour forces, as well as human and environmental health ^{2, 3}. A clean air is a fundamental requisite for human health and well-being ⁴.

According to WHO report, 9 out 10 people globally live in places exceeding the limit of air quality guideline, resulting to 4.2 million people die annually due to the exposure to air pollution, these statistics are highest in low- and middle-income countries ¹. Studies have shown air pollution as a risk factor for cardiovascular and respiratory morbidity, and mortality ^{5, 6, 7, 8}. For instance, respiratory problems, headaches, dizziness, heart attacks were associated with the following air pollutants, CO, NO₂, SO₂, O₃ and particulate matter ^{5, 9}. Specifically, the PM₁₀ lead to bronchitis, heart attacks, asthma, reduced lung function and mortality ⁵.

Globally, the urban cities are usually faced with poor air quality ^{10, 11, 12}. This is mainly attributed to urbanization, industrialization. and increase in number of population and vehicles with its associated activities that lead to the emission of pollutants into ambient atmosphere ^{5, 10, 12}. Some of these pollutants are oxides of sulphur (SO₂), oxides of nitrogen (NO2), carbon monoxide (CO), ammonia (NH₃), hydrogen sulphide (H₂S), ozone (O₃), volatile organic compounds (VOC), heavy metals, polycyclic aromatic hydrocarbons (PAHs) and suspended particulate matter (SPM).

The city of Port Harcourt is one of the cities in Nigeria that is densely populated and occupied with commerce and industrial activities. The city is the capital of Rivers State, one of major oil producing states in the country. Recently, the city is facing the challenges of black soot and other environmental hazards occasioned by legal and illegal oil activities. Hence, this study aimed to ascertain the environmental safety of Port Harcourt metropolis for human habitation by evaluating the air quality index.

2. Materials and Methods

The study involved a descriptive and evaluative study of the Port Harcourt’s air quality index. The air quality data of eleven stations of Port Harcourt metropolis were monitored. The stations were Oil Mill, Trans-Amadi, Amadi-Ama, Borikiri, Lagos Bus-stop, Rumuola, Mile One, Agip Roundabout, Rumuokoro, and Waterlines. The air parameters evaluated were CO₂, NO₂, SO₂, and PM_2.5.

Air Quality Index (AQI) which is the measure of how polluted the air is, will be determined by the equation 1 ¹³.

(1)

Where AQI = Air Quality Index

C = The Average Pollutant Concentration

C_low = The Concentration Breakpoint that is ≤ C

C_high = The Concentration Breakpoint that is ≥ C

I_low = The Index Breakpoint Corresponding to C_low

I_high = The Index Breakpoint Corresponding to C_high

C_pHigh, C_pLow, AQI_High and AQI_Low are from USEPA Pollutant Breakpoints.

The AQI enables the Health Risk to be estimated. It is easy to interpret air quality data because of the reduction of complexity involved with concentration of air pollutants. Index value > 100 indicates the pollutant level exceeds the air quality standard. This is unhealthy first, for some sensitive groups of people, and then for everyone as AQI values increases. Analysis was done using Microsoft Excel software. According to Jafari et al., (2017) ⁵ the classification of AQI is shown in Table 1.

3. Results and Discussion

This study aimed to evaluate the air quality index of Port Harcourt, to identify the safe location and month for human habitation. The AQI cut-off was based on the USEPA and WHO standard guidelines. From this study, the CO₂ and SO₂ had the lowest average monthly concentration in September, whereas the lowest average concentration of NO₂ and PM_2.5 was observed in October. Furthermore, the highest average monthly concentration of CO₂ and NO₂ was reported in May. SO₂ and PM_2.5 was reported highest in August and October 2020 respectively. This is shown in Table 2.

In Table 3, carbon monoxide AQI values in Port Harcourt were observed good throughout the study period (AQI<50), except in November that was observed moderate quality (AQI=58.56). In all the monitoring stations, good quality air was observed in the May, August, and December. In September and October, all the stations had good air quality, except for Oil Mill (AQI=93.00) and Waterlines (AQI=60.30) September, and Amadi-Ama (AQI=68.50), Lagos bus stop (AQI=56.80), and Mile One (AQI=96.40). In November, the AQI for Agip junction was 218.08, Oil Mill was 108.27, Trans-Amadi, and Lagos Bus was observed to be 88.40 and 60.20, respectively. The AQI of CO₂ was reported as good or moderate based on the WHO air quality standard. The estimate was highest in November and lowest in May.

In Table 4, nitrogen dioxide AQI values in Port Harcourt were observed to be good (AQI<50) in August, October, and November, while in May, September, and December moderate air quality was observed (AQI is between 71.56 and 85.53). In the month of May, Rumuola, Mile One, Agip Junction and Rumuokoro the AQI were observed Unhealthy for Sensitive Groups. The other stations the AQI were observed good air quality.

In August, all the locations were observed to having good air quality except Rumuola with AQI = 114.24, categorized as Unhealthy for Sensitive Groups. All the locations had moderate air quality in the month of September while the air quality was good in all the locations in the months of October and November. Like CO₂ the AQI values of NO₂ in all the months was less than 100, with its highest being reported in December (AQI=85.53) and the lowest in August (AQI=20.67).

In Table 5, Oxides of Sulphur quality indices were below the detection limit in September, November, and December. Whereas, in May and August the air quality was unhealthy for sensitive groups. And very unhealthy in October (AQI=250.03).

In May, the air quality in Trans-Amadi and Amadi-ama with respect to oxides of sulpur was Very Unhealthy (AQI > 200), Borikiri, Lagos Bus-stop, Rumuola and Waterlines were unhealthy for sensitive groups while the other stations were between good and moderate.

In August, all the stations were observed unhealthy for sensitive groups and unhealthy except Oil Mill (AQI=97.49) and Rumuola (AQI=68.59) were categorized as having moderate air quality, and Agip junction (AQI=267.88) air quality. The air quality in October was categorized as Very Unhealthy (AQI>200) at all the sampled stations except Agip Junction which was categorized as Hazardous (AQI>300). In all the month of study, the AQI values of SO₂ were above 100, depicting unhealthy and hazardous for habitation.

Regarding PM_2.5, Table 6 revealed that in May and October the air quality was classified as good (AQI <50), while in the other months were classified moderate (AQI = 74.60-90.50). The Table further revealed that in May, the air quality was good in all the locations except in Waterlines (AQI = 141.63) and Rumuola (AQI = 84.44). In August, the stations with unhealthy air quality were Borikiri, Mile One and Rumuokoro while other stations had moderate air quality. In September, Oil Mill was classified unhealthy for sensitive groups and unhealthy at Amadi-Ama.

In October, the air quality was good except in Waterlines (AQI = 112.08). The AQI were higher in the months of November and December. Oil Mill had the highest AQI in November while Waterlines had the highest in December. Comparatively, the result of this study is like previous studies conducted in Rivers State, Nigeria ^{14, 15}.

4. Conclusion

The AQI values indicate that the air quality was good or moderate with respect to CO₂ and NO₂, unhealthy with respect to SO_2, and moderate for PM_2.5 especially at sites with high human activities. Air quality is a function of the level of human activities, especially those that result in the emission of noxious air pollutants. This indicates that the city of Port Harcourt is fairly safe for human habitation. It is recommended that the air quality be put under regular monitoring to regulate the human activities such as open-air combustion of refuse and artisanal refining of crude petroleum that can impact on the air quality, and to making the city safer for human habitation.

References