Environmental Issues: Local, Regional and Global

Environmental issues can be sorted by the scale at which their causes and effects operate. Local issues arise from activities in one place and mostly affect that place: garbage piles in a ward, traffic noise, a polluted pond, indoor smoke from biomass stoves. Regional or transboundary issues cross administrative borders but stay within a region: acid rain falling downwind of industrial areas, haze in Southeast Asia from forest and peat fires in Indonesia, river pollution along the Ganga basin, groundwater depletion in north-western India, the Aral Sea. Global issues affect the Earth system as a whole and need international action: climate change, stratospheric ozone depletion, biodiversity loss, ocean acidification and plastic in the oceans. The same pollutant can fall in more than one category, which is why questions usually give clear examples.

Primary pollutants are emitted directly (sulphur dioxide, nitrogen oxides, carbon monoxide, particulate matter, lead, VOCs), while secondary pollutants form in the atmosphere from reactions (ground-level ozone, peroxyacetyl nitrate or PAN, sulphuric acid mist). Particulate matter is classified by size: PM10 (diameter 10 micrometres or less) and PM2.5 (2.5 micrometres or less), and PM2.5 reaches deepest into the lungs. Photochemical smog (Los Angeles type) forms when nitrogen oxides and hydrocarbons react in sunlight; classical or sulphurous smog (London type, the Great Smog of 1952) forms from smoke and SO2 in cold, humid conditions. A temperature inversion traps pollutants near the ground, which explains severe winter smog in the Indo-Gangetic Plain, made worse by stubble burning, vehicles, construction dust and low wind speed. Indoor air pollution (biomass stoves, tobacco smoke, VOCs, radon, mould) is a major health issue in rural homes.

• Acid rain: rainwater with pH below 5.6, caused by SO2 and NOx; harms lakes, forests, soils and marble monuments

• Air (Prevention and Control of Pollution) Act: 1981

• National Air Quality Index (launched 2014): 8 pollutants (PM10, PM2.5, NO2, SO2, CO, O3, NH3, Pb); categories Good, Satisfactory, Moderate, Poor, Very Poor, Severe (0 to 500)

• National Clean Air Programme (2019); Graded Response Action Plan for Delhi-NCR; Bharat Stage VI norms from April 2020; catalytic converters reduce CO, NOx and hydrocarbons; electrostatic precipitators remove particulates; wet scrubbers remove SO2

Water pollution comes from sewage, industrial effluents, agricultural runoff, oil spills, thermal discharge and solid waste. Key indicators are BOD (oxygen needed by microbes to decompose organic matter), COD (oxygen needed for chemical oxidation), dissolved oxygen, turbidity (measured in NTU), hardness (calcium and magnesium salts) and coliform bacteria, with E. coli indicating faecal contamination. Cultural eutrophication is nutrient enrichment by human activity, producing algal blooms, hypoxia and 'dead zones' such as the one in the Gulf of Mexico. Groundwater faces over-extraction, seawater intrusion in coastal aquifers, and geogenic contamination by arsenic (West Bengal and Bangladesh delta) and fluoride. A water-stressed country, by the Falkenmark indicator, has less than 1,700 cubic metres per person per year, and below 1,000 is water scarcity.

• Water (Prevention and Control of Pollution) Act: 1974, which created the Central and State Pollution Control Boards

• Namami Gange Programme (approved 2014), Ganga Action Plan (1985), Jal Jeevan Mission

• MARPOL deals with pollution from ships; ballast water carries invasive species; red tides are dinoflagellate blooms

• Secondary treatment of sewage uses biological processes such as activated sludge

• Tannery effluents (Kanpur) carry chromium

Soil is degraded by erosion (water erosion as sheet, rill and gully; wind erosion), salinization and sodification (high evaporation plus irrigation without drainage), waterlogging, acidification, compaction, loss of organic carbon through intensive tillage, and contamination by pesticides, heavy metals (cadmium from phosphate fertilizers), industrial waste and landfill leachate. Water is the main agent of soil erosion in India, and the Chambal ravines are the standard example of gully erosion. Gypsum is used to reclaim sodic soils. Bioremediation uses microbes and phytoremediation uses plants to clean contaminated soil. Persistent organic pollutants are covered by the Stockholm Convention (2001), and endosulfan spraying in Kasaragod (Kerala) became a well-known health tragedy. The Soil Health Card Scheme began in 2015, and contour ploughing, terracing, shelterbelts and zero tillage conserve soil.

Noise is unwanted sound, measured in decibels (dB) on a logarithmic scale, so an increase of 10 dB means ten times the intensity. Normal conversation is about 60 dB, prolonged exposure above about 85 dB can damage hearing, and the threshold of pain is about 120 to 130 dB. In India the Noise Pollution (Regulation and Control) Rules, 2000 were framed under the Environment (Protection) Act, 1986.

Day time is 6 a.m. to 10 p.m. and night time is 10 p.m. to 6 a.m. A silence zone extends at least 100 metres around hospitals, educational institutions and courts. Green belts and noise barriers reduce urban noise.

Waste is managed on a hierarchy: prevent and reduce first, then reuse, recycle, recover energy, and dispose in a sanitary landfill last. Landfill gas is mainly methane and carbon dioxide, and leachate pollutes groundwater. Incineration of chlorinated plastics can release dioxins and furans. Composting and vermicomposting (Eisenia fetida) convert organic waste, biogas comes from anaerobic digestion, and pyrolysis is thermal decomposition without oxygen.

• Solid Waste Management Rules, 2016: segregation at source into wet, dry and domestic hazardous waste

• Plastic Waste Management Rules, 2016 with Extended Producer Responsibility; minimum thickness of carry bags raised to 120 microns from 31 December 2022; identified single-use plastic items banned from 1 July 2022

• Bio-medical Waste Management Rules, 2016: yellow bag for human anatomical waste

• E-Waste (Management) Rules, 2016; Seelampur in Delhi is a known informal e-waste hub; Hazardous and Other Wastes Rules, 2016; Basel Convention on transboundary movement of hazardous waste

• Microplastics are plastic particles smaller than 5 mm; the Great Pacific Garbage Patch is in the North Pacific

Weather is the short-term state of the atmosphere while climate is the long-term average of weather. The natural greenhouse effect keeps the Earth about 33 degrees Celsius warmer than it would otherwise be (about minus 18 degrees Celsius without it); the enhanced greenhouse effect is the extra warming caused by anthropogenic gases. Carbon dioxide contributes the most to warming because of its quantity, methane is about 25 to 30 times more potent per molecule over 100 years (rice paddies, livestock, landfills), nitrous oxide comes mainly from fertilizer use, and sulphur hexafluoride has the highest global warming potential among common gases. Feedbacks matter: melting ice reduces albedo and absorbs more heat, and thawing permafrost releases methane. Sulphate aerosols have a cooling effect (global dimming), while black carbon from incomplete combustion warms the atmosphere and darkens snow.

• UNFCCC adopted in 1992; IPCC established 1988 by WMO and UNEP; IPCC Special Report on 1.5 degrees Celsius published in 2018

• Impacts: sea level rise (thermal expansion plus ice melt), coral bleaching, ocean acidification from CO2 absorption, heat waves, changing monsoon, glacier retreat in the Himalaya (the 'Third Pole'), loss of crop yields in the tropics, spread of vector-borne diseases, climate-displaced people, threat to low-lying islands such as Tuvalu and the Sundarbans delta

• El Nino is the unusual warming of the eastern and central equatorial Pacific

• India: National Action Plan on Climate Change (2008) with 8 National Missions

• Ozone depletion: CFCs and halons release chlorine and bromine that destroy ozone catalytically; the ozone hole forms over Antarctica; ozone is measured in Dobson units; harmful effects of UV-B include skin cancer and cataract