---
title: "Exhaust pollutants and emission norms"
subject: "Automotive Technology"
chapter: 10
key: "semester_5/automotive_technology:emission-norms-and-pollutants"
source: https://www.bctengineer.com/q/semester_5/automotive_technology/emission-norms-and-pollutants
site: BCT Engineering
---

# Exhaust pollutants and emission norms

Automotive Technology · Chapter 10: Emissions and Emission Control Systems

- Asked in: year not given, 6 marks
- Video: [What is Emission Standard For Pollution Control| Euro-I and  Euro-II| BS1,BS2,BS3,BS4 and BS6](https://www.youtube.com/watch?v=ysvwiF5ryR4) — PK Classes
- Answer checked by Claude Opus 5.5 (high effort) on 2026-10-14
- Page: https://www.bctengineer.com/q/semester_5/automotive_technology/emission-norms-and-pollutants
- Whole chapter: https://www.bctengineer.com/md/semester_5/automotive_technology/chapter-10

## Question

Name the main pollutants from vehicle exhaust, their causes and their health effects. Briefly explain the emission norms (Euro, BS-VI and EPA) and the main differences between BS-IV and BS-VI.

## Short answer

Vehicle exhaust pollutants: CO from incomplete combustion reduces blood oxygen; HC unburnt fuel causes smog; NOx from high temperature causes acid rain; PM from diesel damages lungs. BS-VI (Euro6) limits sulfur to10 ppm. Compared to BS-IV, diesel NOx drops from0.25 to0.08 g/km, PM from0.025 to0.0045, requiring DPF and SCR.

## Answer

#### Pollutants

| Pollutant | Cause | Effect |
|---|---|---|
| Carbon monoxide (CO) | Incomplete combustion in a rich mixture | Reduces the oxygen carried by blood; toxic |
| Hydrocarbons (HC) | Unburnt fuel, quench layer, evaporation | Smog; some are carcinogenic |
| Oxides of nitrogen (NOx) | High combustion temperature with excess oxygen | Acid rain, smog, lung irritation |
| Particulate matter (PM), smoke | Diesel: rich zones and fuel droplets | Lung and heart disease |
| Sulphur dioxide ($SO_2$) | Sulphur in fuel | Acid rain |
| Carbon dioxide ($CO_2$) | Complete combustion of fuel | Greenhouse gas |

Petrol engines mainly emit CO, HC and NOx; diesel engines mainly emit NOx and PM.

#### Emission norms

Norms are legal limits on the mass of pollutants per km (cars) or per kWh (heavy engines), measured over a standard test cycle.

- **Euro norms (Europe):** Euro 1 (1992) to Euro 6. The limits are tightened at each step; for example, for diesel cars NOx fell from 0.50 g/km (Euro 3) to 0.08 g/km (Euro 6).
- **Bharat Stage (BS) norms (India):** based on the Euro norms; BS-VI is equivalent to Euro 6 and was introduced in April 2020, skipping BS-V.
- **EPA (USA):** Tier 3 and California LEV standards, in g/mile, with a fleet average.

#### BS-IV vs BS-VI

- Sulphur in fuel falls from 50 ppm to 10 ppm.
- The petrol car NOx limit falls from 0.08 to 0.06 g/km; diesel NOx falls by about 70 % (0.25 to 0.08 g/km) and PM by about 80 % (0.025 to 0.0045 g/km).
- Diesels need a DPF and SCR, many GDI engines need a GPF, and on-board diagnostics (OBD-II) and real-driving-emission (RDE) tests are required.

## Check yourself

The answer's key points as multiple-choice questions, with the correct option and why.

1. What causes CO and what is its health effect?
   A. High temperature; acid rain
   B. Complete combustion; greenhouse gas
   C. Fuel sulphur; acid rain
   D. Incomplete combustion in a rich mixture; reduces oxygen carried by blood
   Answer: D. A rich mixture gives CO, which displaces oxygen in blood. (Key point: CO)

2. What causes NOx?
   A. High combustion temperature with excess air
   B. Rich mixture
   C. Evaporation of fuel
   D. Sulphur in fuel
   Answer: A. Nitrogen and oxygen combine at high temperature. (Key point: NOx)

3. Which pollutants dominate in diesel engines?
   A. NOx and PM
   B. CO, HC and NOx
   C. Only SO2
   D. Only CO2
   Answer: A. Petrol engines mainly emit CO, HC and NOx; diesel engines NOx and particulates. (Key point: Engine type)

4. What changes from BS-IV to BS-VI?
   A. Sulphur in fuel falls from 50 to 10 ppm; diesel NOx and PM fall greatly; DPF, SCR and RDE are needed
   B. Only petrol limits change
   C. BS-VI equals Euro 4
   D. Sulphur rises from 10 to 50 ppm
   Answer: A. BS-VI is equivalent to Euro 6 and skipped BS-V. (Key point: BS-IV vs BS-VI)

## Related in Automotive Technology

- [Electric vehicle architecture and traction motors](https://www.bctengineer.com/question.md?key=semester_5%2Fautomotive_technology%3Aev-architecture-and-motors) — Automotive Technology, chapter 12
- [Catalytic converter, EGR, EVAP and DPF](https://www.bctengineer.com/question.md?key=semester_5%2Fautomotive_technology%3Aemission-control-devices) — Automotive Technology, chapter 10

## Related in other subjects

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- [Particulate pollutants: sources and effects](https://www.bctengineer.com/question.md?key=semester_7%2Fenvironment_and_pollution_control%3Aparticulate-pollutants-sources-effects) — Environment and Pollution Control, chapter 1
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