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English · हिन्दी · తెలుగు · தமிழ் · മലയാളം · मराठी · ಕನ್ನಡ

Air pollution and its control

मराठीत स्पष्टीकरण

Pollution · Part 1 / 3 · Fact-checked on · how we check

Written with AI from the sources listed at the bottom of this page, then fact-checked by a separate AI.

Primary and secondary pollutants; particulate matter and the main gases; sources of India's air pollution and its winter peak; classical and photochemical smog and temperature inversion; acid rain and the Taj Trapezium Zone; the 2009 air quality standards, the National Air Quality Index, NCAP, GRAP and the Commission for Air Quality Management; vehicle norms and cleaner fuels.

Each idea is explained first in Marathi (मराठी), ending with the English and Hindi exam terms, followed by the same point in exam English. UPSC Prelims is in English or Hindi, so understand it in Marathi and revise it in English.

प्रदूषण म्हणजे हवा, पाणी, मातीत हानी करेल इतक्या प्रमाणात काहीतरी मिसळणे. हवा प्रदूषण आधी, कारण श्वास थांबवता येत नाही. प्राथमिक प्रदूषक थेट धुराड्यातून किंवा सायलेन्सरमधून येतो. दुय्यम प्रदूषक हवेतच तयार होतो, उन्हात दोन पदार्थ मिळून नवे विष शिजवल्यासारखा; उदाहरण जमिनीलगतचा ओझोन. (→ English: pollutant; primary pollutant; secondary pollutant; ground-level ozone · हिन्दी: प्रदूषक; प्राथमिक प्रदूषक; द्वितीयक प्रदूषक; भू-स्तरीय ओज़ोन)

In exam EnglishPollution means adding to air, water or soil a substance or form of energy, such as noise or heat, in amounts that harm living things or property; the substance itself is the pollutant. This chapter has three parts: air pollution here, water, soil and noise in the second, and waste with its rules in the third. Air comes first because it does the most damage to health: nobody can choose not to breathe, and fine particles reach deep into the body. A primary pollutant leaves its source already harmful, as sulphur dioxide does from a coal-fired chimney or carbon monoxide from an exhaust pipe. A secondary pollutant never leaves a chimney or a pipe; it is created in the air itself as other pollutants react, often with sunlight's help; ground-level ozone is the standard example.

कणीय पदार्थ म्हणजे हवेत तरंगणारे बारीक कण: धूळ, काजळी, राख. PM10 नाकात, घशात अडकतो, चाळणी मोठे खडे अडवते तसा. PM2.5 केसापेक्षा तीसपट बारीक; फुफ्फुसाच्या खोलवर आणि रक्तातही जातो, म्हणून हृदयविकारालाही कारण. धुळीतून मोठे कण येतात; जाळण्यातून, म्हणजे इंजिन, चूल, शेतातील आग, बारीक कण येतात. (→ English: particulate matter; PM10; PM2.5 · हिन्दी: कणिकीय पदार्थ; PM10; PM2.5)

In exam Englishparticulate matter is the pollutant that matters most for health in India. It is a mix of tiny solid or liquid bits suspended in the air: dust, soot, ash, salts and droplets. PM10 covers particles of 10 micrometres or less across, which lodge in the nose, throat and upper airways. PM2.5 takes in the still finer particles, 2.5 micrometres or smaller, so tiny that a single strand of hair is roughly thirty times as wide; these slip deep into the lungs and the finest pass into the blood, which links them with heart disease and stroke as well as asthma and lung cancer. Coarse particles come mostly from road and construction dust and from grinding. Fine particles come mainly from burning, in engines, power plants, brick kilns, stoves and fields, and some form in the air from gases such as sulphur dioxide and ammonia. So PM2.5 is both a primary and a secondary pollutant.

प्रत्येक वायूचा एक स्रोत: सल्फर डायऑक्साइड कोळसा जाळण्यातून, नायट्रोजन ऑक्साइड वाहनांतून. कार्बन मोनॉक्साइड रक्तात ऑक्सिजनची जागा बळकावतो, बसमध्ये आपल्या सीटवर दुसरा बसावा तसा; म्हणून बंद खोलीत कोळशाची शेगडी धोकादायक. वर आकाशात ओझोन रक्षण करतो, खाली श्वासात तोच हानी करतो. शिसे पेट्रोलमधून यायचे, आता नाही. (→ English: sulphur dioxide; nitrogen oxides; carbon monoxide; ground-level ozone; lead · हिन्दी: सल्फ़र डाइऑक्साइड; नाइट्रोजन ऑक्साइड; कार्बन मोनोऑक्साइड; भू-स्तरीय ओज़ोन; सीसा)

In exam EnglishThe main gases each have a typical source and effect. Sulphur dioxide comes chiefly from burning coal and heavy oil in power plants, smelters and refineries; it irritates the lungs and is a parent of acid rain. Nitrogen oxides form whenever fuel burns hot, so vehicles and power plants are the main sources; they also feed acid rain and ozone. Carbon monoxide, from incomplete burning, binds to haemoglobin far more readily than oxygen does and starves the body of oxygen, which is why a charcoal stove in a closed room can kill. Ground-level ozone, formed from nitrogen oxides and hydrocarbons in sunlight, damages lungs and crops; it is the same gas as in the protective layer high in the stratosphere, but harmful when breathed. Lead once came mainly from leaded petrol, which India had phased out by 2000. Ammonia, largely from fertiliser and animal waste, helps form fine particles.

आपल्या हवेतील घाणीचे अनेक स्रोत: रस्त्यावरील वाहने, कारखाने, वीटभट्ट्या, धूळ. ऑक्टोबर-नोव्हेंबरमध्ये पंजाब, हरियाणातील शेतकरी गव्हासाठी भाताचा पेंढा जाळतात. घरातील चुलीचा धूर सर्वाधिक आयांना आणि मुलांना लागतो. हिवाळ्यात वारा हलत नाही, झाकलेल्या भांड्यातील वाफेसारखा धूर तिथेच अडकतो; म्हणून नोव्हेंबरमध्ये दिल्लीची हवा सर्वात वाईट. (→ English: crop-residue burning; indoor air pollution; winter pollution · हिन्दी: पराली दहन; घरेलू वायु प्रदूषण; शीतकालीन प्रदूषण)

In exam EnglishIndia's dirty air has many sources, and their shares differ by city and season. Vehicles dominate along busy roads; coal-fired power plants, steel, cement and brick kilns load the air around industrial belts; road and construction dust adds large amounts of coarse particles. In October and November, farmers in Punjab and Haryana burn rice straw to clear fields quickly for wheat, and the smoke drifts over the plains. Households add a hidden share: smoke from wood, dung and crop waste burnt in stoves fills kitchens, so indoor air pollution falls hardest on the women and children who spend most time near the fire. In the north Indian winter, cool calm air close to the ground and light winds mean pollution is not carried away, which is why Delhi's air is usually worst in November.

धुरके दोन प्रकारचे. एक थंडी, ओलाव्यात कोळशाचा धूर धुक्यात मिसळून येणारे; 1952 मध्ये लंडनमध्ये हजारो लोक मेले. दुसरे प्रकाश-रासायनिक धुरके: ऊन, उष्णता, वाहतूक असताना ऊन वाहनांच्या धुरावर काम करून ओझोन बनतो; लॉस एंजेलिस हे उदाहरण. तापमान व्युत्क्रम म्हणजे वर उबदार हवा झाकणासारखी बसणे; खालचा धूर बाहेर जात नाही. (→ English: classical smog; photochemical smog; temperature inversion · हिन्दी: पारंपरिक धूम-कोहरा; प्रकाश-रासायनिक धूम-कोहरा; तापमान व्युत्क्रमण)

In exam EnglishSmog comes in two kinds. Classical or sulphurous smog forms in cold, damp weather when smoke and sulphur dioxide from coal mix with fog; it is chemically reducing, and the London smog of December 1952 caused thousands of deaths in a few days. photochemical smog needs the opposite conditions: warm, sunny, dry weather and heavy traffic. Sunlight acts on nitrogen oxides and hydrocarbons from exhausts to produce ozone and other irritants such as peroxyacetyl nitrate (PAN); this oxidising brown haze was first studied in Los Angeles in the 1940s. A temperature inversion makes either kind worse. Normally air cools with height, so warm polluted air near the ground rises and spreads. When a layer of warmer air sits above cooler surface air, as on long winter nights, it acts like a lid and keeps pollution trapped close to where people breathe.
Classical and photochemical smog compared
FeatureClassical (sulphurous) smogPhotochemical smog
WeatherCold, damp, foggyWarm, sunny, dry
Main ingredientsCoal smoke and sulphur dioxideNitrogen oxides and hydrocarbons from traffic
Chemical natureReducingOxidising
Key productsSulphuric acid droplets, sootOzone, PAN, aldehydes
Classic caseLondon, December 1952Los Angeles, 1940s

साधा पाऊसही थोडा आंबट असतो; प्रदूषण मिसळले की आणखी आंबट होऊन आम्ल पाऊस बनतो. कोळसा आणि वाहनांच्या धुरातील वायू हवेत आम्लांत बदलून शेकडो किलोमीटर प्रवास करतात. तळ्यांत मासे मरतात, पाने खराब होतात. संगमरवरावर लिंबाचा रस ओतला की बुडबुडे येतात तसे, आम्ल ताजमहालाचा दगड खाते; म्हणून 1996 मध्ये न्यायालयाने भोवतीचे कारखाने हलवायला सांगितले. (→ English: acid rain; pH 5.6; Taj Trapezium Zone · हिन्दी: अम्लीय वर्षा; pH 5.6; ताज ट्रेपेज़ियम ज़ोन)

In exam Englishacid rain is rain, snow, fog or dry deposits made acidic by pollution. Clean rain is already slightly acidic, at a pH of about 5.6, because carbon dioxide dissolves in it; rain is called acid rain when its pH falls below that. Sulphur dioxide and nitrogen oxides, rising from power plants, smelters and traffic, change in the air into sulphuric and nitric acids, and winds can carry them hundreds of kilometres before they fall. It kills fish in lakes, harms leaves and eats into metal and stone. Marble is especially exposed, because the acid reacts with its calcium carbonate. Concern for the yellowing marble of the Taj Mahal led the Supreme Court in 1996 to act in the Taj Trapezium Zone, an area of about 10,400 sq km around the monument where polluting coal-based industries were ordered to shift to natural gas or relocate.

हवा स्वच्छ आहे का हे मोजण्यासाठी 2009 मध्ये 12 प्रदूषकांना मर्यादा ठरवल्या, परीक्षेत पास होण्याचे गुण ठरवावे तशा. PM2.5 साठी वार्षिक सरासरी 40, एका दिवसासाठी 60; PM10 साठी 60 आणि 100. जागतिक आरोग्य संघटनेचा सल्ला आणखी कडक: वर्षाला फक्त 5, पण तो सल्ला आहे, कायदा नाही. पुन्हा पुन्हा नापास होणाऱ्या शहराला अप्राप्त शहर म्हणतात. (→ English: National Ambient Air Quality Standards; non-attainment city; WHO air quality guidelines · हिन्दी: राष्ट्रीय परिवेशी वायु गुणवत्ता मानक; गैर-प्राप्ति नगर; WHO वायु गुणवत्ता दिशानिर्देश)

In exam EnglishIndia judges clean air by the National Ambient Air Quality Standards, notified by the Central Pollution Control Board in November 2009 under the Air Act. They set limits for 12 pollutants: sulphur dioxide, nitrogen dioxide, PM10, PM2.5, ozone, lead, carbon monoxide, ammonia, benzene, benzo(a)pyrene, arsenic and nickel. The limits for particles are the ones most often asked: for PM2.5, 40 micrograms per cubic metre as an annual average and 60 over 24 hours; for PM10, 60 annually and 100 over 24 hours. These are far looser than the World Health Organization's air quality guidelines of 2021, which advise only 5 micrograms per cubic metre of PM2.5 as an annual average. The guidelines are advice, not law. The CPCB and state boards monitor the air, and a city that keeps failing the standards is called a non-attainment city.

मायक्रोग्राम सामान्य लोकांना कळत नाहीत, म्हणून 2014 मध्ये हवा गुणवत्ता निर्देशांक: एक आकडा, एक रंग. आठ प्रदूषकांपैकी जो सर्वात वाईट त्याचाच आकडा निर्देशांक, वर्गात कमी गुण मिळालेला विषयच निकाल ठरवावा तसा. किमान तीन मोजायला हवेत, त्यात एक PM. कार्बन मोनॉक्साइड आणि ओझोनसाठी 8 तासांची सरासरी, बाकीच्यांसाठी 24 तास. 0 ते 500 पर्यंत सहा रंगांच्या पायऱ्या. (→ English: Air Quality Index; sub-index; averaging period · हिन्दी: वायु गुणवत्ता सूचकांक; उप-सूचकांक; औसत अवधि)

In exam EnglishStandards in micrograms mean little to the public, so in October 2014 the government launched the National Air Quality Index, with the slogan 'one number, one colour, one description'. It is built from up to eight pollutants: PM10, PM2.5, nitrogen dioxide, sulphur dioxide, carbon monoxide, ozone, ammonia and lead. Each pollutant's reading is turned into a sub-index, and the highest sub-index becomes the AQI for that place, so the worst pollutant decides the result rather than an average. An AQI is reported only when at least three pollutants are measured, one of which must be PM10 or PM2.5. Most pollutants are averaged over 24 hours, but carbon monoxide and ozone over 8 hours, since they rise and fall quickly. The scale runs from 0 to 500 in six bands, each with a colour and a health message, shown in the table below.
National Air Quality Index categories
AQI rangeCategoryLikely health effect
0–50GoodMinimal impact
51–100SatisfactoryMinor breathing discomfort to sensitive people
101–200Moderately pollutedDiscomfort to people with lung or heart disease, children and older adults
201–300PoorBreathing discomfort to most people on long exposure
301–400Very poorRespiratory illness on long exposure
401–500SevereAffects healthy people; serious for those with disease

2019 मध्ये राष्ट्रीय स्वच्छ हवा कार्यक्रम आला: सुमारे 130 शहरांनी प्रत्येकी स्वतःचा आराखडा लिहायचा, प्रत्येक घराचे स्वतःचे बजेट असते तसा. आधी 2024 पर्यंत 20-30 टक्के घट हे लक्ष्य, नंतर 2025-26 पर्यंत 40 टक्क्यांपर्यंत. निकाल दाखवला तरच पैसे. हा कार्यक्रम आहे, कायदा नाही. (→ English: National Clean Air Programme; city action plan; non-attainment city · हिन्दी: राष्ट्रीय स्वच्छ वायु कार्यक्रम; नगर कार्य योजना; गैर-प्राप्ति नगर)

In exam EnglishThe National Clean Air Programme, launched by the Ministry of Environment, Forest and Climate Change in January 2019, was India's first national, time-bound plan for clean air. It covers the non-attainment cities and a few others, about 130 in all, each of which must prepare and carry out its own city action plan covering roads, dust, waste burning, industry and vehicles. Its first goal was a 20 to 30 per cent cut in particulate concentrations by 2024 against 2017 levels; the target was later revised to up to 40 per cent by 2025-26. Funds are tied to measured progress in each city. NCAP is a programme, not a law, so it relies on the existing powers of the Air Act and the pollution control boards for enforcement.

दिल्लीचा प्रश्न राज्यांच्या सीमा ओलांडतो, म्हणून खास व्यवस्था. श्रेणीबद्ध योजना म्हणजे ताप वाढेल तसा औषधाचा डोस वाढवणे: निर्देशांक 'वाईट' झाला की पहिला टप्पा, 'अति गंभीर' झाला की चौथा टप्पा; बांधकाम थांबवणे, जुनी डिझेल वाहने रोखणे, शाळा बंद करणे. 2021 पासून ही योजना एक वैधानिक आयोग चालवतो. पेंढ्यासाठी, उभ्या खुंटांमध्येच गहू पेरणारी यंत्रे आणि पेंढा कुजवणारी फवारणी. (→ English: Graded Response Action Plan; Commission for Air Quality Management; crop-residue management · हिन्दी: श्रेणीबद्ध प्रतिक्रिया कार्य योजना; वायु गुणवत्ता प्रबंधन आयोग; पराली प्रबंधन)

In exam EnglishDelhi and its region get special machinery because the problem crosses state borders. The Graded Response Action Plan, first notified in January 2017, lists measures that switch on automatically as air quality worsens. In its revised form it has four stages tied to the AQI: Stage I at 'poor' (201 to 300), Stage II at 'very poor' (301 to 400), Stage III at 'severe' (401 to 450) and Stage IV at 'severe plus' (above 450). Early stages control dust, open burning and diesel generators; later ones halt construction, restrict older diesel vehicles and trucks entering Delhi, and may close schools. Since 2021 the plan has been run by the Commission for Air Quality Management in National Capital Region and Adjoining Areas, a statutory body created by its own Act that replaced the earlier Environment Pollution (Prevention and Control) Authority. For crop residue, the answers include machines that sow wheat through standing stubble and microbial sprays that decompose straw in the field.

1998 मध्ये न्यायालयाने दिल्लीच्या बस, रिक्षा सीएनजीवर न्यायला सांगितल्या. नव्या वाहनांसाठी भारत स्टेज नियम: स्टेज वाढला की धूर कमी व्हायला हवा, इयत्ता वाढली की अभ्यास कठीण होतो तसा. आपण BS-V ओलांडून थेट BS-VI वर उडी मारली, 1 एप्रिल 2020 पासून. पेट्रोलमध्ये इथेनॉल मिसळण्याचे लक्ष्य 2025-26 साठी 20 टक्के. घरातील धूर कमी करण्यासाठी उज्ज्वला गॅस जोडण्या. (→ English: compressed natural gas; Bharat Stage VI; ethanol blending; Pradhan Mantri Ujjwala Yojana · हिन्दी: संपीडित प्राकृतिक गैस; भारत स्टेज VI; एथेनॉल मिश्रण; प्रधानमंत्री उज्ज्वला योजना)

In exam EnglishVehicles and fuels show how courts and policy pushed change. In July 1998 the Supreme Court ordered Delhi's buses, taxis and auto-rickshaws to move to compressed natural gas. Emission limits for new vehicles follow the Bharat Stage norms, modelled on European standards; the higher the stage, the less sulphur in fuel and the lower the allowed emissions. India decided to skip BS-V and move straight from BS-IV to BS-VI, and in 2018 the Supreme Court held that no BS-IV vehicle could be sold from 1 April 2020, the date BS-VI took effect across the country. Blending ethanol made from sugarcane and grain into petrol cuts imports and some emissions; the National Policy on Biofuels, as amended in 2022, set 20 per cent blending as the target for 2025-26. Indoors, the Pradhan Mantri Ujjwala Yojana, launched on 1 May 2016, gives poor households LPG connections in place of smoky solid fuels.

हा भाग एक साखळी: स्रोतातून प्रदूषण, हवेत नवे प्रदूषण, हवामान ते अडकवून ठेवते, मग हानी. उपाय त्याच साखळीने उलटा: मानके, निर्देशांक, शहर आराखडा, दिल्लीचे आणीबाणी टप्पे, स्वच्छ इंधन. स्वयंपाकघरात धूर आला तर आधी चूल पाहतो, मग खिडकी उघडतो; तसेच स्रोत आणि परिस्थिती दोन्ही महत्त्वाचे. (→ English: source; standard; response · हिन्दी: स्रोत; मानक; प्रतिक्रिया)

In exam EnglishThe pieces of this part fit into one chain. Sources, from exhausts and chimneys to stubble fires and kitchen stoves, release primary pollutants; sunlight and chemistry turn some of them into secondary ones such as ozone and part of PM2.5; weather, especially winter inversions, decides how long they stay near the ground; and their effects range from damaged lungs to acid rain on marble. The response follows the same chain in reverse. The 2009 standards define what clean air legally means, the AQI translates readings for the public, NCAP sets city-level targets, GRAP and the Commission for Air Quality Management act in emergencies around Delhi, and cleaner fuels and vehicle norms cut emissions at the source. The next part applies the same approach to water, soil and noise.

Exam traps

Recap

Practice questions

Q1. Which one of the following is a secondary air pollutant?

  1. Carbon monoxide
  2. Sulphur dioxide
  3. Ground-level ozone
  4. Lead
Show answer

Answer: C. Ground-level ozone

Ground-level ozone is not emitted directly; it forms when sunlight acts on nitrogen oxides and hydrocarbons. Carbon monoxide comes straight out of exhausts, sulphur dioxide straight out of coal-burning chimneys, and lead was released directly from leaded petrol, so all three are primary pollutants.

Q2. Consider the following statements about photochemical smog:
1. It forms most readily in cold, damp and foggy weather.
2. Ozone and peroxyacetyl nitrate (PAN) are among its products.
Which of the statements given above is/are correct?

  1. 1 only
  2. 2 only
  3. Both 1 and 2
  4. Neither 1 nor 2
Show answer

Answer: B. 2 only

Statement 2 is correct. Statement 1 is wrong: cold, damp, foggy weather suits classical (sulphurous) smog, while photochemical smog needs warm sunshine. Options 1 and 3 include statement 1 and fail; option 4 fails because statement 2 is true.

Q3. Rain is generally described as 'acid rain' when its pH falls below about:

  1. 7.0
  2. 6.5
  3. 5.6
  4. 3.0
Show answer

Answer: C. 5.6

Clean rain is already slightly acidic, at about pH 5.6, because carbon dioxide dissolves in it; acid rain is rain below that level. A pH of 7 is neutral, so it would wrongly make all normal rain acid rain; 6.5 has no special meaning here; and 3.0 is an extreme value seen only in badly polluted places, not the threshold.

Q4. Consider the following statements about the National Air Quality Index:
1. The AQI of a place is the average of the sub-indices of all pollutants measured.
2. Carbon monoxide and ozone are assessed on 8-hour averages.
3. At least one of PM10 and PM2.5 must be among the pollutants measured.
Which of the statements given above are correct?

  1. 1 and 2 only
  2. 2 and 3 only
  3. 1 and 3 only
  4. 1, 2 and 3
Show answer

Answer: B. 2 and 3 only

Statements 2 and 3 are correct. Statement 1 is wrong: the AQI is the highest sub-index, so the worst pollutant decides it. Options 1, 3 and 4 all include statement 1 and are therefore wrong.

Q5. Under the National Ambient Air Quality Standards, 2009, the annual average limit for PM2.5 is:

  1. 5 micrograms per cubic metre
  2. 40 micrograms per cubic metre
  3. 60 micrograms per cubic metre
  4. 100 micrograms per cubic metre
Show answer

Answer: B. 40 micrograms per cubic metre

India's annual PM2.5 limit is 40. Five is the WHO's 2021 guideline, which is advice rather than India's standard; 60 is the 24-hour limit for PM2.5 (and the annual limit for PM10); 100 is the 24-hour limit for PM10.

Q6. Match List I with List II:
List I
A. Graded Response Action Plan
B. National Clean Air Programme
C. National Air Quality Index
D. Commission for Air Quality Management
List II
1. Launched in 2014 to report air quality as one number and colour
2. Statutory body for Delhi and NCR created in 2021
3. Stage-wise emergency measures for Delhi and NCR, first notified in 2017
4. National time-bound programme for cities, launched in 2019
Select the correct answer using the code given below:

  1. A-3, B-4, C-1, D-2
  2. A-4, B-3, C-1, D-2
  3. A-3, B-4, C-2, D-1
  4. A-2, B-4, C-1, D-3
Show answer

Answer: A. A-3, B-4, C-1, D-2

GRAP is the staged emergency plan (2017), NCAP the city programme (2019), the AQI the one-number index (2014) and CAQM the statutory commission (2021). Option 2 swaps GRAP and NCAP; option 3 swaps the AQI and CAQM; option 4 swaps GRAP and CAQM.

Q7. Consider the following statements:
1. India moved directly from Bharat Stage IV to Bharat Stage VI emission norms, skipping Bharat Stage V.
2. The Supreme Court ordered Delhi's public transport to shift to compressed natural gas in 1998.
Which of the statements given above is/are correct?

  1. 1 only
  2. 2 only
  3. Both 1 and 2
  4. Neither 1 nor 2
Show answer

Answer: C. Both 1 and 2

Both statements are correct: BS-VI replaced BS-IV on 1 April 2020 with no BS-V stage, and the CNG order came in July 1998. Options 1 and 2 leave out a true statement, and option 4 rejects both.

Q8. Smog in the cities of the north Indian plains is usually worst in early winter mainly because:

  1. photochemical reactions are strongest in winter sunshine
  2. calm winds and temperature inversion trap pollutants near the ground while crop-residue smoke adds to them
  3. acid rain is most frequent in winter
  4. vehicles are not used in the monsoon season
Show answer

Answer: B. calm winds and temperature inversion trap pollutants near the ground while crop-residue smoke adds to them

Calm air and inversions keep pollution close to the ground, and stubble smoke from October and November adds to it. Photochemical smog is a warm, sunny-weather problem, not a winter one; acid rain does not create smog; and vehicles run all year, so the monsoon difference comes from weather, not from fewer vehicles.

All partsNext: Part 2 →

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