Abstract
<title>Abstract</title> <p>Town growth, more vehicles on the road, seasonal tourism and a few industrial pockets are steadily changing the air over the Indian Himalaya. What is missing is a study that places these very different land uses next to each other and measures the gap. That is what we set out to do here, for five places in Himachal Pradesh: Solan (urban), Baddi (industrial) and the tourist hill towns of Shimla, Kullu and Manali. Daily records came from the public AQI.in platform and cover 25 June to 24 July 2026 – 30 days at each town, 150 site-days altogether. Every record carried the Air Quality Index (AQI) plus PM2.5, PM10, CO, SO2, NO2 and O3. We worked through them with descriptive statistics, time-series plots and Pearson correlation. Mean AQI ranked Baddi (109.1 ± 23.2) > Solan (95.7 ± 22.5) > Kullu (51.8 ± 14.8) > Shimla (47.6 ± 11.4) > Manali (37.4 ± 13.6). Mean PM2.5 spanned 9.5 µg m- ³ at Manali to 39.0 µg m- ³ at Baddi, and PM10 12.4 to 58.4 µg m- ³ across the same pair of sites. Baddi crossed an AQI of 100 on 19 of 30 days and Solan on 13; none of the three hill towns reached that level even once. In the pooled data, AQI tracked PM2.5 (r = 0.995) and PM10 (r = 0.938) almost perfectly. The link with O3 was moderate (r = 0.472), NO2 weak and positive (r = 0.243), CO weak and negative (r = −0.255), and SO2 essentially absent (r = 0.024). Whatever else was in the air, particulates set the index through the whole month. The record therefore leaves behind a workable baseline for air quality management in the state, and a demonstration of how far open monitoring data can be pushed when urban, industrial and tourist settings are read against one another. The work is presented as a case study of five Himachal Pradesh towns rather than a state-wide survey.</p>