Air pollution under the microscope |04 January 2024
Dr Sam
There was an anomalous spike in the AQI (Air Quality Index) on the third day after the December 7 explosion, where for the whole day, the air pollution was elevated over all regions.
This is the observation shared by Dr Laurent Sam from local environment group, Sustainability for Seychelles (S4S), when giving his views to Seychelles NATION about air quality in the aftermath of the incident.
Seychelles has been monitoring air quality since November last year, following the installation of 13 Air quality monitoring sensors to measure the concentration of air pollutants in the country (refer to story on page 6). It now joins over 6,000 cities in 117 countries which are monitoring their air quality.
Dr Sam noted that despite the observation of an elevated level of air pollution over all regions, more research is required to establish a direct link between the pollution and the explosion. However, it could have been the dust from the explosion that had spread across to all the regions covered by the monitoring stations, he said.
The Air quality monitoring stations were installed by S4S in collaboration with the Seychelles Meteorological Authority (SMA) and comprised 10 sensors on Mahé, two on Praslin and one on La Digue.
Given there were two rainy days before December 7, and the day of the explosion was a sunny day, Dr Sam explained it could be the rain suppressed the dust, prior to the explosion, and this was re-suspended back into the air as things dried and the water evaporated.
“The weather has a big impact on where the air pollution goes after it is produced. Things like precipitation, wind speed and direction, air pressure, humidity and temperature all affect air quality. The Seychelles Meteorological Authority has the expertise to analyse these factors and their combined effects to better understand the air pollution,” said Dr Sam.
Speaking on data collected in November and December 2023, Dr Sam said that in the first half of November, the AQI was elevated to about 50 on average, reaching a peak of 90 at certain times. He added that people who suffered from asthma would have felt their symptoms worsen during those times but going through December, the wind direction and speed changed, and the AQI improved.
He explained that rain can reduce air pollution by 10% to 20% by washing the pollutants out of the air. The heavier the rain, the more pollutants are washed to the ground. After the rain, as the water evaporates from the ground, some of the particulate matter can become re-suspended into the air. However, the wind which often accompanies the rain has a greater effect by blowing away the air pollution and preventing it from stagnating and concentrating in an area.
Generally, there were some days where the air quality was worse at La Misère than in Victoria. “This was interesting, because one might associate the mountains with better air quality. On reflection however, it is not always the case. Because of the topography, if the wind is blowing the air pollution into the valley of La Misère, the pollutants become concentrated into a smaller volume of air, raising the AQI. This is a good example of how the data from the air quality sensors can challenge our preconceived beliefs,” said Dr Sam, who noted that the initial data indicates that not everything is perfect but neither is it all bad.
In 2016, the Yale Environmental Performance Index declared that Seychelles had the best air in the world. Six years later, in 2022, Seychelles was ranked 36th in the world for air quality by the same organisation.
Looking specifically at particle pollution from fine particulates (PM2.5), which is a concern when levels in air are unhealthy, Seychelles was ranked 94th in the world in 2022, with a score of 31.2 out of 100 compared to a score of 39.2 just two years earlier. Furthermore, according to the WHO, in 2022, the annual average PM2.5 concentration in Seychelles was 17 µg/m3, or 3 times their air quality guideline of 5 µg/m3.
Dr Sam said that at first glance, these statistics are surprising and some may understandably struggle to accept them. After all, Seychelles is supposed to be a net carbon sink, with green and dense vegetation, and coastlines lush with sea grass, and the country prided itself on environmental protection policies and a natural beauty that attracts tourists.
However, he added, the trees and sea grass do not absorb PM2.5 pollutants from the air in the same way they absorb carbon dioxide. The air pollution produced locally will remain in the region and be breathed in by everyone until it is sufficiently dispersed by the wind or the rain.
Dr Sam said long-term exposure to air pollution has been linked to poor lung development, an increase in asthma prevalence and severity, accelerated ageing, and several chronic conditions such as cardiovascular and respiratory diseases including lung cancer, leading to reduced life expectancy.
“All this suggests that the air in Seychelles is not as clean as most people expect, and there are real health consequences that have slowly crept up on us. Some may argue that international organisations like Yale and WHO have got their statistics wrong and that our country cannot possibly have such bad air. Yet, if we can celebrate first place for air quality, we should be able to accept 36th prize from the same organisation, and we should be able to reclaim first place if we can correct our mistakes,” he concluded.
Compiled by Patrick Joubert