Fig. 5: Clustering analysis of the 45 analysed sites based on their formaldehyde (HCHO) and nitrogen dioxide (NO2) column densities from OMI and the HCHO/NO2 ratios (FNR).
From: Ozone trends and their sensitivity in global megacities under the warming climate
Units for HCHO and NO2 are ×1015 mol cm−2, and FNR is dimensionless. Each point represents a site. Sites are grouped into distinct clusters using the K-means algorithm. Colour coding highlights the different clusters, with clusters indicating regions with similar ozone sensitivities due to similar FNR. The sites assigned to each cluster are as follows: Cluster 0: Mexico City, Jakarta, Buenos Aires, São Paulo, Los Angeles, Dhaka, Mumbai, Kolkata, Karachi, Bengaluru, Chengdu, Istanbul, Chongqing, Rio de Janeiro, Chennai, and Lima. Cluster 1: Amazon rainforest and Congo rainforest. Cluster 2: Lagos, Kinshasa, Bogotá, Sahara Desert, Manila, Bangkok, Ho Chi Minh, Luanda, and Great Victoria Desert. Cluster 3: New York City, Pearl River Delta, Tokyo, Delhi, Johannesburg, Seoul, Cairo, Yangtze River Delta, Beijing–Tianjin, Moscow, Osaka, Lahore, Tehran, Xi’an, Paris, Zhengzhou, London, and Wuhan.
