A Shot of Smoke for Delhi

Each November, satellites detect massive plumes of smoke and heightened hearth exercise in northwestern India as farmers burn off extra paddy straw after the rice harvest. Many farmers, significantly within the states of Punjab and Haryana, use hearth as a quick, low-cost approach to clear up and fertilize fields earlier than planting winter wheat crops. Nonetheless, the surge of fires within the coronary heart of the densely populated Indo-Gangetic Plain usually contributes to a pointy deterioration of air high quality in November and December.

Although lingering monsoon rains this yr saved hearth exercise at low ranges for a couple of weeks longer than typical, satellites noticed elevated hearth exercise in November because the tempo of burning accelerated. On November 11, 2021, the Seen Infrared Imaging Radiometer Suite (VIIRS) on the Suomi NPP satellite tv for pc acquired this natural-color picture of a river of smoke streaming from fires in Punjab and Haryana towards Delhi, one in every of India’s most populous cities. Use the picture comparability slider to see the places of hotspots noticed by VIIRS that afternoon. Fires in northern Pakistan possible contributed a few of the smoke as effectively.

“Wanting on the dimension of the plume on November 11 and the inhabitants density on this space, I’d say {that a} conservative estimate is that at the least 22 million folks had been affected by smoke on this in the future,” stated Pawan Gupta, a Universities Area Analysis Affiliation (USRA) scientist at NASA’s Marshall Area Flight Heart.

As in years previous, sensors in Delhi and elsewhere in northern India have recorded hovering ranges of air air pollution. Sensors within the capital space—together with one on the U.S. Embassy—recorded concentrations of advantageous particulate matter (PM_2.5) and coarse particulate matter (PM₁₀) effectively above 400 micrograms per cubic meter on a number of events in November. Since particulate matter is linked to a variety of respiratory, cardiovascular, and different well being issues, World Well being Group tips suggest that 24-hour imply PM_2.5 concentrations be saved under 15 micrograms per cubic meter. The excessive air pollution ranges led to partial lockdowns, faculty closures, and halts in building in Delhi and different cities.

Smoke from crop fires isn’t the one contributor to the hazy skies. Influxes of mud generally arrive from the Thar Desert to the west—as they did on November 12, 2021 (see picture under). An array of different human-caused sources of air air pollution in cities, together with motorcar fumes, industrial and building exercise, fireworks, and fires for heating and cooking additionally produces particulate matter and different pollution.

Geography and climate additionally exacerbate the area’s air high quality issues. Temperature inversions are frequent in November and December as air rolls off the Tibetan Plateau and mixes with smoky air from the Indo-Gangetic plain. An inversion can perform like a lid, with the nice and cozy air trapping pollution close to the floor and serving to hem pollution in between the Himalayan Mountains to the north and the Vindhya Mountains to the south.

Hiren Jethva, a Universities Area Analysis Affiliation (USRA) scientist based mostly at NASA’s Goddard Area Flight Heart, makes use of measures of the “greenness,” or Normalized Distinction Vegetation Index (NDVI) to anticipate hearth exercise every year. The information he makes use of comes from the Reasonable Decision Imaging Spectroradiometer (MODIS) on NASA’s Aqua satellite tv for pc.

“Earlier in the summertime, we noticed one of many largest NDVI values within the 20-plus yr file. Based mostly on that, I predicted this might be one of the lively hearth seasons on file, and that’s precisely what we’ve got seen,” stated Jethva. “We nonetheless have a couple of weeks of burning to go, however already Aqua MODIS has detected greater than 17,000 hotspots in Punjab and Haryana—making this probably the most lively hearth season on file.” Aqua MODIS started amassing information in 2002.

The Seen Infrared Imaging Radiometer Suite (VIIRS) sensor makes comparable measurements, however it might detect many small and low-temperature hotspots that MODIS misses. As of November 16, VIIRS had detected greater than 74,000 hotspots in Punjab. “That’s approaching the almost 85,000 the sensor detected in 2016, probably the most lively yr within the VIIRS file,” stated Gupta.

Whereas complete hearth counts have remained persistently excessive in Punjab, satellite tv for pc information point out that campaigns to get farmers to clear fields with out utilizing hearth have confirmed extra profitable in Haryana. “Over 9 years of VIIRS commentary, we don’t see a lot of a pattern in Punjab. Nonetheless, in Haryana, we noticed a forty five p.c lower within the complete variety of fires in 2020 in comparison with the 2012-2019 common,” Gupta added. “However hearth counts appear to be on the upper finish in Haryana once more this yr.”

NASA Earth Observatory photographs by Lauren Dauphin, utilizing MODIS information from NASA EOSDIS LANCE and GIBS/Worldview. Story by Adam Voiland.