Active and passive air quality bio-monitoring in the tropics: Intra-urban and seasonal variation in atmospheric particles estimated by leaf saturated isothermal remanent magnetisation of Ficus benjamina L (Moraceae)

摘要

Atmospheric pollutant emissions are likely to increase continously in developing cities like Abidjan (Ivory Coast) where air quality strategies are ineffective or not yet implemented. This could result in a big risk to human health. Local meteorological parameters can have both positive or negative effect on habitat quality depending on the biomonitoring approach used. This study investigates the sources and factors affecting the spatio-temporal variation in particulate pollution in a tropical area in Abidjan (Ivory Coast) using a passive and active biomonitoring approach. Leaf saturated isothermal remanent magnetisation (SIRM) of Ficus benjamina L. was monitored for 2-6 months over 2 consecutive years in four distinct urban land use classes (main roads, industrial zones, residential zones and parks) based on several meteorological parameters (wind speed, temperature, relative humidity and precipitation) and season. Results showed leaf SIRM varied among land use classes and season with main roads and industrial zones presenting higher leaf SIRM during the dry season. This suggests that vehicular exhaust emissions and industrial smokestacks were the main sources of particulate matter (PM) pollution in Abidjan. These results show also the contribution of natural particles from harmattan dust during the dry season. Leaf SIRM was negatively correlated with precipitation intensity, suggesting a wash-off effect of particles on leaves. Results, however, differed between the dry and wet season. During the dry season, leaf SIRM of young leaves was higher than that of old leaves. This trend was reversed during the raining season. This suggests combined effects of meteorology and plant growth/physiology.