RSPM (Respirable Suspended Particulate Matter)

RSPM (Respirable Suspended Particulate Matter) is the dust fraction of ambient air consisting of particles 10 µm or smaller — the size range that bypasses the upper respiratory tract and lodges in the bronchi and alveoli. It is identical in definition to PM10 and has gradually been replaced by the term PM10 in Indian regulatory documents since the 2009 NAAQS revision, although SPCB consent conditions and CPCB online dashboards still routinely use RSPM.

The Indian ambient limit, set under NAAQS 2009, is 100 µg/m³ as a 24-hour average applicable uniformly to industrial, residential, rural and ecologically-sensitive areas — India dropped the earlier two-tier industrial/residential split. The annual mean limit is 60 µg/m³. By contrast, the WHO 2021 air quality guideline recommends 15 µg/m³ (24-hour) and 15 µg/m³ (annual), giving Indian limits roughly 4-7x more lenient than WHO.

Measurement uses a Respirable Dust Sampler — a high-volume sampler fitted with a size-selective cyclone inlet that removes particles above 10 µm, so only PM10 collects on the downstream filter. Sampling duration is typically 24 hours at 1.1 m³/min. Modern continuous instruments use beta-attenuation monitoring (BAM) or tapered-element oscillating microbalance (TEOM) for hourly readings, which is what CPCB CAAQMS stations report on the public dashboard.

For recycling plants — tyre shredders, plastic granulators, biomass dryers, e-waste workshops — RSPM is the parameter SPCB inspectors check at fence-line monitors during routine CTO audits. Source-side controls include enclosure of shredders and conveyor transfer points, hood-capture ductwork sized at 0.75-1.0 m/s capture velocity, and a downstream baghouse sized for 0.8-1.2 m/min air-to-cloth ratio. Cyclones alone are insufficient for PM10 because they cut at roughly 10 µm; the fine half of RSPM passes through. Water-spray suppression at shredder feed reduces fugitive RSPM by 40-70% at modest water cost. Compliance failure on RSPM is the most common reason SPCBs issue closure directions to small recycling units.