Mexico raised its alert level on the Popocatepetl volcano Sunday following in increase in tremors and explosions of ash that shuttered airports in nearby Mexico City and Puebla…A panel of experts recommended raising the alert level to “yellow phase three” from “yellow phase two” on the volcano, located 70 km (44 miles) southeast of Mexico City, the country’s head of civil protection, Laura Velazquez, said in a press conference.