New Delhi: As the air quality index in Delhi continues to hover in the low to mid-200s and in one instance also reaching 300, experts have raised concerns over the development, citing the fact that previously such air quality levels were not recorded in summers and were mostly a phenomenon of smoke-choked winters.As per meteorological experts, the reason behind this unusual summer pollution is dust lifted from the deserts and semi-arid regions of Rajasthan by the hot, dry winds blasting through northwest India, the impact of which was earlier minimised by the Aravalli mountain ranges, which for centuries acted as a natural barrier, reported Hindustan Times.However, decades of mining, quarrying and encroachment, have resulted in environmental degradation in the Aravallis, with dust now moving through it unimpeded.“The Aravalli hills – both the long continuous ranges as well as the hundreds of thousand smaller hills play a critical role in controlling the spread of sand from the western Thar deserts. The hills typically slow down winds from the west, which shed their sandy loads on the western flanks and these sands form sandy obstacle dunes,” Chetan Agarwal, a forest analyst who has studied the region in detail, told the newspaper.In a study conducted by Jindal School of Environment and Sustainability (JSES) and Indian Institute of Technology Kharagpur researchers, it was found that in just seven years between 2017 and 2024, built-up areas in the region grew by 53%, or 2,644 sq km, primarily replacing croplands and rangelands.The HT report added that when the study was published in March, the dean of JSES at OP Jindal Global University had said that mining activities, especially lead-zinc, marble, sandstone, and industrial minerals, were placing significant pressure on the landscape, with high number of active leases that cause geomorphic disturbance.