Abstract

The 10-year observations of the atmospheric molar fractions of CO₂, CH₄ and CO in West Africa were analyzed using a high precision measurement of the Lamto (LTO) station (6°31 N and 5°02 W) in Côte d’Ivoire. At daily scale, high concentrations appear at night with significant peaks around 7 a.m. local time and minimum concentrations in the afternoon for CO₂ and CH₄. The CO concentrations show two peaks around 8 h and 20 h corresponding to the maximum in road traffic of a northern motorway located 14 km from the station. The long-term increase rates of CH₄ (∼7 ppb year⁻¹) and CO₂ (∼2.24 ppm year⁻¹) at Lamto are very close to global trends. The variations of the concentrations of the three gases show strong seasonality with a peak in January for all gases and minima in September for CO₂ and CH₄, and in June for CO. The CO variation suggests a significant impact of fires on the CO, CO₂ and CH₄ anomalies in the Lamto region during the dry season (December to February). CO and CH₄ show strong correlations (at synoptic-scale and monthly based) in January (r = 0.84), February (r = 0.90), April (r = 0.74), November (r = 0.79) and December (r = 0.72) reflecting similar sources of emission for both gases. The trajectories of polluted air masses at LTO, also indicate continental sources of emission associated with Harmattan winds.

摘要

使用高精度测量科特迪瓦Lamto（LTO）站（6°31 N和5°02 W）对西非的CO ₂，CH ₄和CO的大气摩尔分数进行了10年观测。象牙 在每日范围内，高浓度出现在晚上，当地时间上午7点左右出现明显的峰值，下午的最低浓度为CO ₂和CH ₄。一氧化碳浓度分别在8小时和20小时左右出现两个峰值，分别对应于距车站14公里的北部高速公路的道路交通量最大值。CH ₄（〜7 ppb年^-1）和CO ₂（〜2.24 ppm年^-1）的长期增长率）在Lamto与全球趋势非常接近。三种气体浓度的变化表现出强烈的季节性变化，所有气体的峰值均在1月达到峰值，CO ₂和CH ₄的峰值在9月最低，CO的峰值在6月。CO的变化表明，火灾对CO产生了重大影响，干旱季节（12月至2月），Lamto地区的CO ₂和CH ₄异常。CO和CH ₄在1月（r =  0.84），2月（r =  0.90），4月（r =  0.74），11月（r =  0.79）和12月（r = 0.72）反映了两种气体的相似排放源。LTO处受污染的空气质量的轨迹也表明与哈曼丹风有关的大陆排放源。