Smog, or smoke fog, is a type of intense air pollution. The word "smog" was coined in the early 20th century, and is a portmanteau of the words smoke and fog to refer to smoky fog due to its opacity, and odor. The word was then intended to refer to what was sometimes known as pea soup fog, a familiar and serious problem in London from the 19th century to the mid-20th century, where it was commonly known as a London particular or London fog. This kind of visible air pollution is composed of nitrogen oxides, sulfur oxide, ozone, smoke and other particulates. Man-made smog is derived from coal combustion emissions, vehicular emissions, industrial emissions, forest and agricultural fires and photochemical reactions of these emissions.
Tehran is the capital and largest city of Iran and the largest city in Tehran Province. It also serves as the capital of the province, county and the Central District. With a population of around 9 million in the city and around 16 million in the larger metropolitan area of Greater Tehran, Tehran is the most populous city in Iran and Western Asia, and has the second-largest metropolitan area in the Middle East, after Cairo. It is ranked 24th in the world by metropolitan area population.
Exhaust gas or flue gas is emitted as a result of the combustion of fuels such as natural gas, gasoline (petrol), diesel fuel, fuel oil, biodiesel blends, or coal. According to the type of engine, it is discharged into the atmosphere through an exhaust pipe, flue gas stack, or propelling nozzle. It often disperses downwind in a pattern called an exhaust plume.
Environmental issues in Iran include, especially in urban areas, vehicle emissions, refinery operations, and industrial effluents which contribute to poor air quality. A report by the United Nations Environment Programme ranked Iran at 117th place among 133 countries in terms of environmental indexes. Water scarcity is a serious issue, and the country is also threatened by climate change.
Pollution in China is one aspect of the broader topic of environmental issues in China. Various forms of pollution have increased as China has industrialised, which has caused widespread environmental health problems.
Air pollution is the contamination of air due to the presence of substances called pollutants in the atmosphere that are harmful to the health of humans and other living beings, or cause damage to the climate or to materials. It is also the contamination of the indoor or outdoor environment either by chemical, physical, or biological agents that alters the natural features of the atmosphere. There are many different types of air pollutants, such as gases, particulates, and biological molecules. Air pollution can cause diseases, allergies, and even death to humans; it can also cause harm to other living organisms such as animals and crops, and may damage the natural environment or built environment. Air pollution can be caused by both human activities and natural phenomena.
Road space rationing, also known as alternate-day travel, driving restriction and no-drive days, is a travel demand management strategy aimed to reduce the negative externalities generated by urban air pollution or peak urban travel demand in excess of available supply or road capacity, through artificially restricting demand by rationing the scarce common good road capacity, especially during the peak periods or during peak pollution events. This objective is achieved by restricting traffic access into an urban cordon area, city center (CBD), or district based upon the last digits of the license number on pre-established days and during certain periods, usually, the peak hours.
Pollution in California relates to the degree of pollution in the air, water, and land of the U.S. state of California. Pollution is defined as the addition of any substance or any form of energy to the environment at a faster rate than it can be dispersed, diluted, decomposed, recycled, or stored in some harmless form. The combination of three main factors is the cause of notable unhealthy levels of air pollution in California: the activities of over 39 million people, a mountainous terrain that traps pollution, and a warm climate that helps form ozone and other pollutants. Eight of the ten cities in the US with the highest year-round concentration of particulate matter between 2013 and 2015 were in California, and seven out of the ten cities in the US with the worst ozone pollution were also in California. Studies show that pollutants prevalent in California are linked to several health issues, including asthma, lung cancer, birth complications, and premature death. In 2016, Bakersfield, California recorded the highest level of airborne pollutants of any city in the United States.
Air Pollution in Mexico City has been of concern to the city's population and health officials for decades. In the 20th century, Mexico City's population rapidly increased as industrialization brought thousands of migrants from all over the world. Such a rapid and unexpected growth led to the UN declaring Mexico City as the most polluted city in the world in 1992. This was partly due to Mexico City's high altitude, which causes its oxygen levels to be 25% lower. Carbon-based fuels also do not combust completely. Other factors include the proliferation of vehicles, rapid industrial growth, and the population boom. The Mexican government has several active plans to reduce emission levels which require citizen participation, vehicular restrictions, increase of green areas, and expanded bicycle accessibility.
Air pollution in the United Kingdom has long been considered a significant health issue, and it causes numerous other environmental problems such as damage to buildings, forests, and crops. Many areas, including major cities like London, are found to be significantly and regularly above legal and recommended pollution levels. Air pollution in the UK is a major cause of diseases such as asthma, lung disease, stroke, cancer, and heart disease, and is estimated to cause forty thousand premature deaths each year, which is about 8.3% of deaths, while costing around £40 billion each year.
Air pollution is the release of pollutants into the air that are detrimental to human health and the Earth. In Canada, air pollution is regulated by standards set by the Canadian Council of Ministers of the Environment (CCME), an inter-governmental body of federal, provincial and territorial Ministers responsible for the environment. Air pollution from the United States and to lesser extent Canada; caused by metal smelting, coal-burning for utilities, and vehicle emissions has resulted in acid rain, has severely impacted Canadian waterways, forest growth, and agricultural productivity.
Mobile source air pollution includes any air pollution emitted by motor vehicles, airplanes, locomotives, and other engines and equipment that can be moved from one location to another. Many of these pollutants contribute to environmental degradation and have negative effects on human health. To prevent unnecessary damage to human health and the environment, environmental regulatory agencies such as the U.S. Environmental Protection Agency have established policies to minimize air pollution from mobile sources. Similar agencies exist at the state level. Due to the large number of mobile sources of air pollution, and their ability to move from one location to another, mobile sources are regulated differently from stationary sources, such as power plants. Instead of monitoring individual emitters, such as an individual vehicle, mobile sources are often regulated more broadly through design and fuel standards. Examples of this include corporate average fuel economy standards and laws that ban leaded gasoline in the United States. The increase in the number of motor vehicles driven in the U.S. has made efforts to limit mobile source pollution challenging. As a result, there have been a number of different regulatory instruments implemented to reach the desired emissions goals.
Road space rationing in Beijing was introduced in the city in a permanent basis after successful results obtained with the policy during the 2008 Summer Olympics. Road space rationing or driving restriction is a transportation demand management regulation aimed to reduce traffic by restricting automobile travel through means such as restriction of cars that could enter common road space based upon the last digits of the license number on certain established days during certain periods in Beijing. The main objective of this restraint policy in Beijing is to reduce the amount of exhaust gas generated by motor vehicles.
Air pollution in India is a serious environmental issue. Of the 30 most polluted cities in the world, 21 were in India in 2019. As per a study based on 2016 data, at least 140 million people in India breathe air that is 10 times or more over the WHO safe limit and 13 of the world's 20 cities with the highest annual levels of air pollution are in India. 51% of the pollution is caused by industrial pollution, 27% by vehicles, 17% by crop burning and 5% by other sources. Air pollution contributes to the premature deaths of 2 million Indians every year. Emissions come from vehicles and industry, whereas in rural areas, much of the pollution stems from biomass burning for cooking and keeping warm. In autumn and spring months, large scale crop residue burning in agriculture fields – a cheaper alternative to mechanical tilling – is a major source of smoke, smog and particulate pollution. India has a low per capita emissions of greenhouse gases but the country as a whole is the third largest greenhouse gas producer after China and the United States. A 2013 study on non-smokers has found that Indians have 30% weaker lung function than Europeans.
The 2013 Eastern China smog was a severe air pollution episode that affected East China, including all or parts of the municipalities of Shanghai and Tianjin, and the provinces of Hebei, Shandong, Jiangsu, Anhui, Henan, and Zhejiang, during December 2013. A lack of cold air flow, combined with slow-moving air masses carrying industrial emissions, collected airborne pollutants to form a thick layer of smog over the region. Levels of PM2.5 particulate matter averaged over 150 micrograms per cubic metre; in some areas, they were 300 to 500 micrograms per cubic metre.
The air quality in Delhi, the capital territory of India, according to a WHO survey of 1,650 world cities, and a survey of 7,000 world cities by the US-based Health Effects Institute in August 2022, is the worst of any major city in the world. It also affects the districts around Delhi. Air pollution in India is estimated to kill about 2 million people every year; it is the fifth largest killer in India. India has the world's highest death rate from chronic respiratory diseases and asthma, according to the WHO. In Delhi, poor quality air irreversibly damages the lungs of 2.2 million or 50 percent of all children.
The 1966 New York City smog was a major air-pollution episode and environmental disaster, coinciding with that year's Thanksgiving holiday weekend. Smog covered the city and its surrounding area from November 23 to 26, filling the city's air with damaging levels of several toxic pollutants. It was the third major smog in New York City, following events of similar scale in 1953 and 1963.
Air pollution in Taiwan is mostly derived from sources of domestic combustion, primarily the burning of fossil fuels. Taiwan's topography has been noted to be a contributing factor to its air pollution problem, leading to poor dispersal and trapping pollutants. Taipei, Taiwan's capital and largest city for example, is surrounded by mountains, and other industrial centers along the northern and western coasts of Taiwan are surrounded by high mountains.
Tehran with more than 15 million people population during day time, suffers from severe massive traffic congestion in rush hours.
Environmental issues in North Macedonia include air and water pollution, deforestation, threats to endemic species and climate change. There is substantial degree of pollution in the air, water and land of North Macedonia. According to 2019 estimates, the country is considered to have one of the highest degrees of pollution in Europe.
