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| Fig. 1: Particulate matter classifications based on their sizes. (Source: M. S. Kim) |
Exposure of particulate matter (PM) air pollutants has been a serious environmental and health hazard. The size and constituent of PM are important parameters that determine the adverse health effects. [1,2] PM is often categorized by its size as indicated in Fig. 1, and the representative sizes of PM are below 2.5 µm, denoted as PM2.5, and below 10µm, denoted as PM10, and PM between 10 µm and 2.5 µm is often referred as coarse PM. Fossil fuel combustion, industrial process, and power generation generate most of PM2.5. [3] PM2.5 is composed of a mixture of primary and secondary particulates as well as sulfate and nitrate particles that are generated by conversion from primary sulfur and nitrogen oxide emissions. [4] Specifically, primary and secondary aerosols are the major constituent for PM pollutants. The primary aerosols consist of metals and other elements, and the secondary aerosols are derived from the chemical conversion of gases to aerosols. Below bullet points describe primary and secondary aerosol species and which process they are derived from. [3]
Potassium (From biomass)
Sodium (From sea salt)
Calcium (From cement)
Aluminum, Selenium, Cobalt, Arsenic (From coal burning)
Iron, Zinc, Copper, Lead (From ferrous industries)
Aluminum, Silicon, Calcium (From soil and road dusts)
Vanadium, Nickel, Manganese, Iron (From oil burning)
Elemental carbon, Organic carbon (From biomass, diesel, petrol)
Potassium, Zinc, Lead (From refuse incineration)
Sulfates (From diesel, Coal combustion)
Nitrates (From high-temperature combustion)
Ammonium (From fertilizer usage and animal husbandry)
Volatile organic compounds (From biomass, diesel, petrol, gas combustion)
There is also PM generation from natural disasters such as volcanic eruptions, wildfires, and dust storms that produce SO2, CO2, HF, black/brown carbon, and O3 precursor. [3] Also, the road traffic emits NO, NO2, and carbon black PMs that cause health concerns living in a populated city. Therefore, high demands for clean and renewable energy generation and green energy usage are in great need to mitigate PM air pollution and health issues.
PM is one of the most serious air pollutants that cause cardiovascular diseases. Both outdoor and indoor air quality can affect our health based on air pollution levels and constituents. It is hard to breathe perfectly clean air nowadays due to the inevitable emissions of air pollutants of PM2.5 and volatile organic compounds throughout our daily activities such as commuting, cooking, smoking, etc. It is widely known that air pollution is the most important environmental factor presenting a risk to health and represents a greater disease burden than polluted water, soil contamination, and occupational exposures combined. [5] There is ultrafine PM0.1 that has particle sizes in the nanometer scale, specifically PM size less than 100 nm. The nanometer size of PM adds nanotoxicity. Also, these PM0.1 can disseminate into our bloodstream once inhaled from our lungs, which is known to trigger cardiovascular diseases. [6] Based on the prospective study involving about thirty-three thousand Dutch residents, people who are exposed to PM0.1 exhibited an increased risk of heart failure and heart attack. [7] According to the National Particle Component Toxicity Initiative research program, PM2.5 that derived from oil combustion and road traffic were closely related to short-term adverse health effects, and PM from coal combustion was more related to long-term adverse health effects. [8] Household air pollution is relatively substantial that accelerates the exposure of PM2.5. The global burden of disease study estimated that household air pollution is associated with 2.6 million premature deaths worldwide in 2016. [9] So the household air pollution should be considered seriously. Also, it has been reported that up to 65% of outdoor air particles can be inhaled when people are indoors. [10] The main sources of household air pollution are cooking and heating with biomass fuels. These include cooking on gas stoves, burning incense and candles, using aerosol sprays, and cleaning products. The household air pollution study in China followed up for about 7 years revealed the hazard ratio, known as HR, for cardiovascular mortality of 1.2 with the use of solid fuel for cooking and HR of 1.29 with the use of solid fuel for heating. [11] As 90% of the global population live in areas with PM2.5 exposure, it is crucial to track air qualities around the place that one may spend the most time and also reduce the PM2.5 pollutant levels to mitigate cardiovascularly risks. [3]
The ways to alleviate PM exposure are wearing personal face masks, having household air filtrations, having a healthy diet, exercising, avoiding polluted areas, and staying indoors. As the major PM pollutants are generated from global urbanization and industrialization, obeying practical and clear societal and governmental regulations is critical to control the release of PM air pollutants. Having a mandatory or voluntary reduction in greenhouse gas emissions, transitioning to lower-carbon fuels, legislating the use of electrified vehicles, and increases in fuel taxes will help to mitigate PM generation. [12] Implementations of new air exchange systems and new building designs may bring air pollutant reduction. Trees could adsorb PM on leaf surfaces and absorb gaseous pollutants, and it has been reported that PM2.5 levels near trees are reduced by 7~24%. [13] Wearing N95 masks is one of the most effective ways to reduce personal PM2.5 exposure. There are a variety of types of facial masks. Usually, inexpensive masks are made of cloth, cotton, or gauze and are widely available. However, wearing these masks is not recommended to protect against the risks of PM as their performances are inconsistent and only 15~57% effective. [3] It has been found that disposable surgical masks are slightly more effective than cloth masks in preventing exposure of particles, but N95 respirators are the most effective masks to filter out PM. [14] Indoor air pollution is also a serious health risk factor because the majority of people spend more time indoors than outdoors. An efficient way to reduce indoor air pollutants is having central home air-filtration systems and portable air purifiers. These are able to reduce indoor PM2.5 levels by 50~60%, and using these are more convenient than wearing N95 masks in an indoor environment. [3] Exercising is essential to our health. However, the intensity, duration, and location of exercise are variables that might yield opposing outcomes if people exercise in a highly PM polluted environment. Therefore, a critical point may exist whereby excess breathing of PM pollutants during exercising could outweigh health benefits for exercising. It has been reported that several dietary supplements can reduce the effects of air pollution on the respiratory and cardiovascular health. For instance, taking Vitamin C supplementation can prevent acute lung disease caused by NO2 and ozone gas exposures and also reduce chronic obstructive pulmonary disease and asthma hospitalizations associated with PM10 exposure. [15] Hence, there are diverse ways to prevent chronic exposure to PM pollutants; however, mitigating PM generation from clean energy generation and industrial processes need to be paired with these practices to substantially eliminate PM pollution issues.
© Mun Sek Kim. The author warrants that the work is the author's own and that Stanford University provided no input other than typesetting and referencing guidelines. The author grants permission to copy, distribute and display this work in unaltered form, with attribution to the author, for noncommercial purposes only. All other rights, including commercial rights, are reserved to the author.
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