New Delhi — Authorities in India stepped up efforts on Friday to address deteriorating air quality as farmers burning crop stubble and calmer winter winds left a thick blanket of haze and smog to choke residents across the Delhi capital region. Factories, construction sites and primary schools were ordered to shut down and Delhi authorities urged people to work from home as dangerous fine particle pollution filled the air. Delhi's 24-hour average air quality index (AQI), which measures the concentration of very fine particles know as PM2.5 in the air — particularly harmful pollutants as they're easily inhaled and can settle deep in the lungs — crossed 470 on Friday, per the state-run Central Pollution Control Board. Anything over 300 is classed as "hazardous" on the international AQI rating system, and at "severe" levels, air pollution "affects healthy people and seriously impacts those with existing diseases."   Authorities also restricted the operation of diesel-powered vehicles and