Fig. 7: Pearson correlation analysis among formaldehyde (HCHO), nitrogen dioxide (NO2), temperature (T), and short-wave radiation (SWR) across the 45 analysed sites clustered into four groups.
From: Ozone trends and their sensitivity in global megacities under the warming climate
The colour intensity indicates the strength and direction of the correlation. Darker colours represent stronger positive correlations, and lighter colours indicate negative correlations. 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.
