Atmospheric oxidation capacity and ozone pollution mechanism in a coastal city of Southeast China: Analysis of a typical photochemical episode by Observation-Based Model

A typical multi-day ozone (O3) pollution event was chosen to explore the atmospheric oxidation capacity (AOC), OH reactivity, radical chemistry, and O3 pollution mechanism in a coastal city of Southeast China, with an Observation-Based Model coupled to the Master Chemical Mechanism (OBM-MCM). The hydroxyl radical (OH) was the predominant oxidant (91±23 %) for daytime AOC, while NO3 radical played an important role for AOC during the nighttime (64±11 %). Oxygenated volatile organic compounds (OVOCs, 30±8 %), NO2 (29±8 %) and CO (25±5 %) were the dominant contributors to OH reactivity, accelerating the production of O3 and recycling of ROx radicals (ROx=OH+HO2+RO2). Photolysis of nitrous acid (HONO, 33±14 %), O3 (25±13 %), formaldehyde (HCHO, 20±5 %), and other OVOCs (17±2 %) were the important primary sources of ROx radicals, which played initiation roles in atmospheric oxidation processes. O3 formation was VOC-sensitive, and controlling emissions of aromatics, alkenes, and long-chain alkanes were benefit for ozone pollution mitigation. Combined with regional transport analysis, the reasons for this O3 episode were the accumulation of local photochemical production and regional transport. The results of sensitivity analysis showed that VOCs were the limiting factor of radical recycling and O3 formation, and the 5 % reduction of O3 would be achieved by decreasing 20 % anthropogenic VOCs. The findings of this study have significant guidance for emission reduction and regional collaboration on future photochemical pollution control in the relatively clean coastal cities of China and similar countries.

Caractérisation physico-chimique des eaux d’un système lacustre du cordon littoral ivoirien : cas du lac Labion

L’analyse spatio-temporelle des paramètres physico-chimiques des eaux du lac Labion dans le système lagunaire ivoirien, a été abordé dans un contexte de variabilité climatique. L’objectif est de caractériser la physico-chimie des eaux au cours des saisons climatiques. Pour y parvenir, une analyse hydrologique a été réalisé à partir de mesure in situ des paramètres pH, Température, Conductivité électrique, Oxygène dissous, Matières en suspension, Transparence et Turbidité. Ces paramètres ont été mesurés à l’aide d’un multi-paramètre. Celui-ci est mis à l’eau et les résultats s’affichent à l’écran. Seule la transparence a été mesuré à l’aide du disque de Secchi. La température (31 °C) indique des eaux relativement chaudes. Quant au pH, il varie du neutre (6,79) à alcalin (8,99). La conductivité moyenne sur le lac est de 40 μS/cm. Les eaux sont bien oxygénées (7 à 8 mg/L) et présente peu de matières en suspension. L’analyse en composante principale montre une forte corrélation (r > 0,7) entre les variables température, oxygène, pH et conductivité. Ces résultats mettent en évidence deux (02) mécanismes qui sont à l’origine des forçages naturel et artificiel. Il s’agit du mécanisme de la photosynthèse occasionnant une bonne oxygénation des eaux et du mécanisme de pollution traduisant une forte turbidité.Mots clés : Lac, saison climatique, paramètre, mécanisme, évolution. English Title: Physico-chemical characterization of the waters of a lake system of the ivorian coastal cordon: case of Lake LabionThe spatio-temporal analysis of the physicochemical parameters of the waters of Lake Labion in the Ivorian lagoon system was tackled in the context of climate variability. The objective is to characterize the physico-chemistry of the waters during the climatic seasons. To achieve this, a hydrological analysis was carried out using in situ measurement of the parameters pH, Temperature, Electrical conductivity, Dissolved oxygen, Suspended matter, Transparency and Turbidity. These parameters were measured using a multi-parameter. It is launched and the results are displayed on the screen. Only transparency was measured using the Secchi disk. The temperature (31 °C) indicates relatively warm waters. As for the pH, it varies from neutral (6.79) to alkaline (8.99). The average conductivity on the lake is 40 μS / cm. The waters are well oxygenated (7 to 8 mg / L) and have little suspended matter. The principal component analysis shows a strong correlation (r> 0.7) between the variables temperature, oxygen, pH and conductivity. These results highlight two (02) mechanisms which are at the origin of natural and artificial forcings. This is the mechanism of photosynthesis causing good oxygenation of water and the pollution mechanism reflecting high turbidity.Keywords: Lake, climatic season, parameter, mechanism, evolution.