How do humans cause pollution?

In this blog post, we will discuss “How do humans cause pollution?” Firstly, we will learn about the basics of air pollution. Then, the article will focus on the human causes of air pollution. In the end, the article will provide detailed solutions to improve air quality.

Air pollution can cause detrimental side effects to the humans and rest of the world. It can cause crop productivity loss, degrade human health, and loss of biodiversity. Air pollution also drives climate change. There are two causes of air pollution:

Natural Air Pollution
Anthropogenic Air Pollution

Natural Air Pollution is caused by natural phenomena such as dust storms, wildfires and volcanic eruptions. On the other hand, anthropogenic air pollution is nothing but air pollution caused by human activities.

Since the stone age, humankind has always strived hard to achieve stability and comfort in their life. Finally, we succeeded, which led to the industrial revolution, followed by urbanization and much-needed changes in the lifestyle.

However, in the process of progression, somewhere we left behind the great values of nature, we forgot the support and symbiotic existence of the environment. While human inventions, no doubt, have always helped us to save our lives, it has also given birth to much inevitable stuff. One such thing is air pollution.

The introduction of harmful contaminants in gases, liquid droplets and solid particles into the atmosphere is called air pollution. These toxic agents are known as airborne pollutants. Examples of air pollutants are sulphur oxides, nitrogen oxides, particulates, etc. These can be chemical or biological.

Humans have tremendously exploited natural resources such as fossil fuels in the constant chase of becoming the best in every term and during the development of energy and manufacturing sectors. In general, urban air pollution is not only influenced by anthropogenic or man-made activities but also by natural events. In addition, the air quality in the urban areas can alter due to neighbouring regions.

Here, we will see the man-made causes of air pollution.

Human Causes of Air Pollution

Transportation Sector

Vehicles are one of the significant sources of air pollution. All vehicles generate toxic pollutants such as nitrogen oxides, carbon monoxide, volatile organic compounds, particulate pollution, etc. Besides, greenhouse gases are also emitted from the commutes. They account for 29% of US greenhouse gas emissions. Thus, the transportation sector is the most significant contributor to GHG emissions in the United States. In addition, the combustion of fossil fuels like diesel and gasoline produces carbon dioxide and hydrofluorocarbons that over warm the atmosphere and causes changes in the atmosphere.

As per the United States Environmental Protection Agency (US EPA), the transportation sector is widely responsible for smog conditions. Such smog conditions lead to poor air quality, and it causes detrimental effects on citizens and the environment. The US EPA observed that over 55% of NOx is generated by vehicles while commuting. In comparison, less than 10% of emissions are from volatile organic compounds and particulate matter.

Ozone is formed when heat and sunlight cause chemical reactions between nitrogen oxide and volatile organic compounds. While atmospheric ozone benefits humans and protects the earth from harm, the artificial ozone layer formed in the stratosphere can threaten living organisms.

Short-term exposure to ozone can cause many respiratory ailments, such as inflammation of the lung lining. It can also reduce lung functionality. Brief exposure to ozone can cause shortness of breath, coughing, wheezing, chest pain and burning sensation in the chest. Therefore, EPA has recommended not to exercise outside when ozone levels are high. In addition, exposure to ambient ozone causes asthma, bronchitis and premature mortality. Long-term exposure to ozone can permanently damage lung tissue.

It can also develop asthma in children who frequently exercise outside. Scientific evidence has proved that a weak immune system can cause asthma in children. The study published in the Journal of Allergy and Clinical Immunology of 2010 stated that they examined around 181 children with and without asthma in the California cities of Fresno and Palo Alto. Researchers selected Fresno city kids as this city is known for poor air quality, Palo Alto has comparatively lower air pollution. Mobile sources such as cars and trucks are the leading causes of air pollution in Californian cities.

The research pointed out that sources such as vehicle exhaust, industrial emissions, polyaromatic hydrocarbon (PAH) from the combustion of fossil fuels were responsible for weakening the immune system. Thus, such weakening of the immune system directly corresponded to asthma generation among kids and adults.

Another study published by the United States Environmental Protection Agency (US EPA) in 2018 has found out that airborne pollutants such as ozone and coarse particulate matter can cause asthma in children. They have also estimated that around six million children in the United States are sensitive to air pollution and can cause asthma. The study further highlighted that African American adolescents were more susceptible to air pollution than other children.

Agriculture and Livestock Sector

According to the World Health Organisation (WHO), agriculture consists of various activities such as harvesting, breeding and nurturing farm animals, processing crops and tending gardens and nurseries, etc. The post-harvesting phases consist of vegetable packaging, meat processing, and other processes in conventional agricultural production practices—for example, flour mills, cotton ginners, etc. In the United States, half of the land area, which is nearly a 1.2billion acres, is farmland. These farmlands generate a tremendous supply of crops and other products.

Particulate pollution is produced during various agricultural practices. Firstly, the unpaved roads present in the farmlands can generate particulate pollution containing dust and sand. Such pollution can be transferred by air movements to the nearby areas and cause lung irritation. Then, there are different sorts of machinery used for farming. The exhausts of these machineries also generate various toxic gases such as carbon monoxide, oxides of nitrogen, particulates and sulphur dioxide. While agricultural waste burning is sporadic in the United States, if done, it can produce ash and volatile organic compounds in the air. The pesticides sprayed on the crops can also cause air pollution. Airborne pollutants such as hexachlorobenzene, endrin, etc., are released into the air. The livestock department can also equally produce air pollution and cause a health hazard. The livestock industry has greenhouse gases like methane and other hydrocarbons. The reared pigs can cause asthmatic symptoms in farmers. A high density of pig production can produce excessive amounts of nitrogen and phosphorous.

Indoor Activities

Many household activities such as heating, cooking, cleaning and other miscellaneous activities significantly contribute to indoor air pollution. Indoor pollution contributes to ambient air pollution. Many regular household products such as cleaning sprays, varnish, paints, solvent removers, perfumes, tobacco smoke and incense stick can pollute the air.

Asbestos can also cause deterioration of indoor air. It is found in various products such as home construction materials, and they are commonly detected in paints, coatings, ceilings and floor tiles. Generally, the old products or older houses would be having more presence of this toxic material than the newer ones.

Asbestos can cause shortness of breath, loss of appetite, chest pain, tightness and persistence of dry cough. But the good news is that the United States has banned its use in construction activities and it’s no longer used. Formaldehydes group are colourless gas having a pungent smell. Even though its production has been banned in the United States since 1970, they are still found in paints, sealants and wooden floors. Carpets also use formaldehyde as permanent adhesives.

Radon is one such toxic agent which is found underneath homes. Radon is usually discovered in bedrock and other building materials that cause indoor air pollution. The gases from radon can seep through the basement and cause a significant risk to the residents. Tobacco smoke is also one of the neglected and concerning air pollutants. The study also revealed that pregnant women smoking cigarettes caused a potential threat to the fetus development; the smoke can cause molecular changes. In addition, the tobacco smoke exposure of the mothers caused hindrances in the lung development of the fetus. Researchers further analyzed that such children at early stages and later teens got asthma or experienced asthmatic problems.

You would like to keep fresh flowers keeping in your living room. You also would be having furry friends living with you. Though I am not very keen on plucking flowers or purchasing them to decorate my house, I love doggies and other furry pets. But they all come with one big drawback. They can produce biological pollutants such as pollens, mould, bacteria, viruses and animal dander, developing asthmatic symptoms in people.

Gas appliances such as heaters, wood stoves, space heaters, dryers, fireplaces and space heaters release hazardous pollutants such as carbon monoxide, nitrogen dioxide and particulates. Carbon monoxide and particulates, as mentioned earlier, causes many respiratory and heart-related ailments. High levels of nitrogen dioxide can cause a hazard to the human respiratory tract. It can increase the susceptibility to various respiratory infections and asthma. Prolonged exposure to elevated amounts of nitrogen dioxide can result in chronic lung disease. It can also affect the smelling ability of humans.

The fumes released from the paraffin wax candles causes air to pollute. Research done by South Carolina State University said that paraffin wax releases toxic chemicals such as benzene and toluene indoors. Even the office stationeries such as copiers, laser printers, correction fluids, etc., release volatile organic compounds which deeply penetrate the lungs and inflame their linings. Besides, dry cleaned laundry clothes contain highly toxic substances such as trichloroethylene and perchloroethylene. All the pollutants, as mentioned earlier, can cause throat and nose irritation, flu, dizziness, anaemia and other allergic reactions. They can irritate your respiratory tract too. In addition, toxic chemicals can cause lung cancer and damage vital organs such as the liver, kidney and brain.

Beauty Products

Air experts around the globe also suggest the use of beauty products can contribute to air pollution. The majority of the cosmetics and perfumes available in the market contain toxic pollutants such as volatile organic compounds. These pollutants are released into the air when they are used. Thus, the fashion industry or the increased population using such products can significantly reduce air pollution.

Industrial and Energy Sector

The various industrial process releases massive amounts of organic compounds, greenhouse gases, carbon monoxide, hydrocarbons and chemicals in the air. Researchers observe that considerably large amounts of carbon dioxide, a greenhouse gas, gets released in various production and manufacturing industries. Sometimes, enterprises might not use updated machinery and technologies in their process.

In such cases, outdated technologies can produce a large amount of toxic gaseous waste. The construction and demolition industry also has many airborne pollutants such as particulate matter in the air. Such activities can significantly contribute to the smog conditions and can affect visibility. In addition, the RMC or ready mix concrete plants produce hazardous VOCs and other toxic gases in the air while creating cement and mortar mix. The other pollutants released by all industries are HAPs or hazardous air pollutants, leading to health complications. It can cause cancer, autoimmune diseases, nervous system conditions, respiratory ailments, etc.

The energy sector is also one of the prominent contributors to greenhouse gases. In addition, the energy generation and consumption process can negatively impact human health. This is because fossil fuels like natural gas and coal are used.

Sulphur content coal produce plumes of sulphur oxides, carbon monoxide, ash, black and brown carbon in the air. Sulphur dioxide can further initiate acid rains which damage respiratory and heart health. Again, the particulate pollution creates a hazy condition in cities and can often mix with ozone to make the air unhealthier to breathe. Such conditions can lead to asthma and chronic bronchitis in children and elderly adults. In addition, heavy metals such as mercury are released into the air. Such poisonous gas is a significant risk to the food web and can lead to bioaccumulation.

Nuclear power plants don’t produce the pollutants mentioned earlier, but their wastes are lethal. If the radioactive wastes are not properly disposed of, they can release many toxic gases into the air and soil.

Sewage Plants

Various wastewater treatment plants, refining and desalination plants can contribute to air pollution. Recent research has indicated that these plants generate elevated levels of greenhouse gas emissions (GHG), volatile organic compounds and oxides of nitrogen and sulphur into the atmosphere. Besides, you might have experienced foul odour in the air near these plants and disposal facilities. This is because of the exceeding levels of the airborne microbial count in the air. Such occurrences have increased health concerns among the people working on such plants and nearby residents.

Refineries and Petroleum Industries

Refineries and the Petroleum sector are significant sources of air pollution. This is because they significantly release tremendous amounts of volatile organic compounds. Examples of these volatile organic compounds are o-xylene, toluene and benzene. Besides, they also generate bio-aerosols and air pollutants such as ammonia, methane and hydrogen sulphide. These elements are responsible for the foul odour.

Below, I am providing comprehensive solutions to improve air quality.

What can I do to protect myself from air pollution?

I will elaborate on some of the measures to protect yourself from air pollution.

Personal Hygiene

You can also fight the effects of air pollution by maintaining personal hygiene:

You can cut your nails short to avoid the accumulation of dirt.
You can also practice mouth gargling after coming home to free your mouth from unwanted guests.

You can also brush twice a day to keep airborne infections at bay.
You can also take steam therapy at home to cleanse your lungs.

Quit Smoking

Smoking cigarettes, hookahs (shisha), electric vape or any other types of cigars are not at all suitable for your health. It’s best to stop smoking. Active and passive smoking provides the direct entry of harmful pollutants into your body. This causes the risk to your respiration and other organs dependent on it.

Physical Exercise

Physical activities have many benefits to your body. It not only improves your stamina and immunity levels but also helps to increase your lung capacity. Yoga, sanas, swimming, running, cycling, brisk walking and dancing are some of the best forms of exercise to improve your health.

Breathing Exercise

The majority of people in the world don’t breathe properly. However, correct breathing techniques can keep illnesses due to air pollution at bay. A pranayama is a form of yoga asana which helps to improve breathing methods and lung functionality.

Some of the pranayama types that help you fight air pollution are Kapalbhati, Anulom Vilom, Chandra Nadi, Surya Nadi and Bhastrika. It is strongly recommended to learn this art of breath from a well-certified yoga trainer.

You can also increase your lung muscles by simply taking a deep breath and holding it for a count of 10. Then, slowly breathe out the air. If you can keep your breath for a longer time, then you have good lungs health.

Good diet

Always go for a well-balanced diet to remain fit and strong. Consistent eating of junk and fast food will increase the risk of obesity and other diseases. In addition, such people are more vulnerable to the adverse effects of air pollution. Instead, add more fresh veggies and fruits to your diet. Also, you can consume less meat to minimise carbon footprints.

You can also add anti-inflammatory foods as these types of food help to cleanse your lungs effectively. Anti-inflammatory foods which I recommend are:

Immunity booster drinks

You can do your immunity booster drinks by using readily available items in your kitchen. Immunity booster drinks help to cleanse your lungs. Some of the DIY immunity booster drinks are as follows:

Take a glass of warm white milk. Add half a teaspoon of turmeric powder to it. Also, add two strands of saffron to it. Drink it at night before sleeping. You will get good sleep, and you will be relieved from chest congestion.
Boil water by adding half cinnamon stick. Drink the spice-infused water once a day. Your sinuses would be cleared up.
Buy an excellent green tea. Prepare a green tea by following the packet instructions. Have it whenever you feel irritation in your throat.
Take some crushed 1 or 2 peppercorns, a half-inch of a blade of lemongrass and 1 inch of grated ginger and half a teaspoon of turmeric powder. Add everything in one glass of boiling water and reduce it to half a glass. Drink two tablespoons of this spice-infused warm water every after three hours. Adding honey is optional.
You can also drink warm water and add honey if you want. Honey helps to relieve throat irritation.

Use Mask

Mask can prevent you from inhaling the polluted air. You would be able to work in contaminated areas without any fear of allergy infections and stress.

Masks I recommend

Name	Why I recommend it
BASE CAMP CROSSDUST MASK	EAPI Filter Technology & Advanced NanotechnologyUser FriendlyMore Durable Six layers face maskFilter materials of the dust mask: Double-Layer Melt-blown with Electrostatic Adsorption Performance, Activated carbon, Non-woven Polypropylene
NIOSH approved N95 mask	Four layers mask Flexible nose pad, dual strapsDisposable maskEasy to breathe
BASE CAMP Reusable Cloth Face Mask	Three layers mask; 100% cotton Skin-friendly and breathablePocket to add additional filterReusable Mask

How can I individually reduce air pollution?

You can always try your level best to minimise air pollution. The following are the methods to reduce air pollution at an individual level.

Plant Trees

Encourage tree plantation drives amongst the communities. You can be a green saviour of your region. Trees are the natural air purifiers of the environment, and it supplies us with clean air.

Municipal councils or the local authorities can develop urban forests to increase the green cover of the locality. They can also plan to create vertical green walls to improve oxygen levels of the region naturally. But don’t forget to plant only indigenous trees.

Human/ religious celebrations in eco-friendly ways

Nowadays, many couples celebrate gender (of their baby) revealing parties by bursting firecrackers. But, unfortunately, these firecrackers can transform into massive wildfires if they are burst near trees.

Thus, you can celebrate such celebrations by planting trees in your nearby barren land. Bursting firecrackers on any religious, festive or personal occasion are only going to harm your loved ones.

You can also celebrate Christmas by not cutting Christmas Trees. Instead, you can buy artificial ones and use them in the coming years too.

Discourage Plastic

Single-use plastic has been one of the major concerns in the environment. Plastic pollution indirectly contributes to the degradation of air quality. Plastic, when burned, releases various toxic gases such as dioxins into the air.

Encourage alternative use of the plastic product. For example, you can wear a cloth bag for shopping. You can also carry your travel cutlery set to a restaurant. Additionally, you can take your water bottle instead of purchasing a packaged drinking water bottle every time.

Use of public transportation

Increase the use of public transport to reduce air pollution and traffic congestion. You can also try carpooling or the cab sharing option. Then, you can also use bicycles instead of scooters. Lastly, you can always opt for walking a shorter distance.

Alternative use of fossil fuel

It would be best to try switching to other fuel alternatives. For example, don’t use wood for the fireplace. Instead, you can wear multiple layers of clothes for warmth. In this way, you can conserve energy. Additionally, you can also install solar panels on house roofs to convert solar energy into electricity.

You can also buy electric and hybrid vehicles to minimise tailpipe emissions. Finally, propose or discuss a plan with your mayor or any relevant local authority to promote your region’s renewable energy sector.

Reduction of personal carbon footprints

You can also keep a check on your carbon footprints. For example, you can delete unwanted photos, videos or emails from clouds and email boxes as and when possible. Unfortunately, this unwanted stuff takes a lot of energy, which indirectly contributes to air pollution.

You can also switch off the lights and electrical appliances of the vacant rooms. Try buying local products instead of imported ones. Be vocal about them. You can also discover your own country rather than travelling to different ones.

Create Awareness

Air pollution is unpredictable; air pollution in your vicinity can affect people living in Asia and vice-a-versa. However, you can create public awareness about air pollution amongst your community by teaching and interacting with your kids about the importance of good air.

Educate youth by telling them the ill effects of poor air quality. Then, let your country’s future know that they deserve a better place to live!

How can the local authorities improve the air quality of your region?

You can always observe the changes happening in your surrounding nature. If you experience bad air quality or any activities producing air pollution, you can always concern relevant local authorities or the mayor.

Here are some methods which local authorities can do.

Proper disposal of waste

Improper solid waste management of an area is an invitation to many diseases and infections. In addition, burning solid waste in public can cause air pollution, although such practices are rare in the US.

The wastes are mainly disposed of in the engineered landfills and recycled before final disposal to landfills and waste incinerators.

In addition, waste incinerators help to convert waste into energy.

However, many researchers have claimed that gasification technology or waste-to-energy technology may release harmful gaseous contaminants. Thus, it is necessary that waste collectors rigorously segregate the waste before sending it to waste incinerators.

The best solution is to minimise waste at a personal level. Statistically, 70% of the waste generated can be recycled effectively. Thus, strive to recycle your waste at a personal level as much as possible.

Reducing air pollution from agriculture

Stubble burning is still practised in some parts of the US. This event contributes to the degradation of air. Local authorities can help farmers convert this waste into cattle fodder or be transformed into pellets as fuel. In addition, farmers should stop the usage of harmful pesticides or fertilisers to decrease air pollution.

How can I reduce indoor air pollution?

Maintaining household or indoor hygiene

You can decrease poor air quality by adequately maintaining indoor hygiene. For example, you can frequently clean your cupboards and open decks to avoid an accumulation of dust particles. You can then vacuum your carpets and sofas at least twice a week.

Make sure your doggies and cats are well-groomed. Use chimneys and exhaust fans in kitchens. You can also install an exhaust fan in washrooms. Always make sure you are keeping your house well ventilated.

Keep doors and windows open when possible. Maintain the health of electric appliances such as heaters, humidifiers, AC, fans, air ducts and so on at regular intervals of the year. Avoid overuse of strong perfumes or strong scented candles indoors. You can additionally use indoor plants to make your indoors more lively and fresh.

Indoor plants

Indoor plants do the same work as outdoor ones- they help to purify indoor air naturally. These indoor plants are also easy to maintain.

The indoor plants which I recommend are as follows:

Air purifiers

Air purifiers help to improve indoor air quality. The risk of getting air pollution-related diseases decreases due to the use of air purifiers. Air purifiers having good HEPA filters do an adequate job of filtering pollutants.

Air Purifiers I recommend are as follows:

Name	Why I recommend it
Blueair Pro XL Air Purifier	99.7% of airborne pollutants such as mould, allergens, smoke particles and pollens are captured.
AIRMEGA 400S	Reduction of 99.97% of particulates of 0.3 microns. Also responsible for reducing more than 99% of VOCs, NH3 and CH3CHO.Washable and permanent pre-filters are available
Blueair Pure 121	Includes 3-part filtration system. Captures 99% of common airborne PM 2.5 pollutants such as allergens, odours, smoke, mould spores, dust mites and pet dander.An activated carbon filter removes common odours caused by smoke, pets, and gases (VOCs) and smoke caused by wildfires.

Humidifiers

The humidity levels in the office should be maintained between 30 and 50% in the office. This range helps to keep dust mites, mould and other allergens under control. In addition, when AC or heater makes the air in the room dry, humidifiers can maintain correct humidity levels.

Humidifiers I recommend

Name	Why I recommend it
Amazon Basics Ultrasonic Cool Mist Humidifier	4 litre of tank capacityAuto shut-off feature and 12 or 24-hour timer settingsIt can be used in both seasons
MOVTIP Humidifier	Portable Mini-humidifier500 ml capacity, still produces longer mistsEasy to operate
LEVOIT Humidifier	It can be used for both seasons6 litres of capacity Easy to clean and has a remote control

Dehumidifiers

Dehumidifiers also work similarly to humidifiers. It controls the high levels of humidity in the office.

Dehumidifiers I recommend

Name	Why I recommend it
Pro Breeze Dehumidifier	Can extract 50 pints of moisture a dayEnergy-saving auto-off systemBuilt-in Humidity sensor
HOmeLabs Dehumidifier	Eliminates moistness, odour controllerEasy to cleanRemovable water tank
TCL Portable Dehumidifier	20 pints of moisture removed per dayIt can be operated at low temperatures tooEasy to maintain

Other FAQs about Air Quality that you may be interested in.

How can you prevent air pollution?

How can you save the Earth?

How can you test the air in your house?

Conclusion

We discussed ” How do humans cause air pollution?” in this blog post. Firstly, we learnt about the basics of air pollution. Then, the article focused on the causes of air pollution. In the end, the article provided detailed solutions to improve air quality.

Frequently Asked Questions (FAQs): How do humans cause pollution?

Which pollutants causes chlorosis in plants?

Ozone causes chlorosis in plants. This is because ozone enters into leaves through stomata during typical gas exchange. As ozone is a strong oxidant, it causes several symptoms, including chlorosis and necrosis.

What are the five disastrous effects of air pollution?

The five disastrous effects of air pollution are:

Respiratory and heart ailments in human beings
Global Warming
Acid Rain
Depletion of the ozone layer
Food insecurity

What are the primary cause of air pollution and its effect on the environment?

The burning of fossil fuels is the primary cause of air pollution. Combustion of fossil fuel is needed in the transportation sector, energy generation, and cooking activities. Such activities release a tremendous amount of carbon monoxide and other toxic pollutants into the atmosphere. These contaminants cause harm to human health, hampers flora and fauna growth, and create food insecurity.

How does air pollution affect global warming?

Air pollution also releases greenhouse gases such as carbon dioxide into the atmosphere. This contributes to the greenhouse effect. In addition, the carbon dioxide emitted traps a tremendous amount of heat into the atmosphere. This process results in global warming.

What effect does air pollution have on food crops and biodiversity?

Pollutants such as sulphur can result in excess acidification of the water bodies such as lakes and streams. This pollutant can also damage trees and fertile land. In addition, the atmospheric nitrogen can create an imbalance in biodiversity and harm overall plant communities and aquatic life. Moreover, ozone can damage the tree leaves.

Why air pollution is a problem?

Air pollution is a problem because it harms crops, animals, and plants simultaneously. Air pollution also contributes to the depletion of the ozone layer and aggravate climate change. Some of the environmental effects of air pollution are smog, hazy skies and eutrophication.

References

Arslan, S. & Aybek, A., 2012. Particulate matter exposure in agriculture. IntechOpen. Available at: https://www.intechopen.com/chapters/38344

Causes, effects and solutions to improve indoor air pollution. Conserve Energy Future. Available at: https://www.conserve-energy-future.com/causes-and-effects-of-indoor-air-pollution.php

Fast Facts on Transportation Greenhouse Gas Emissions. EPA. Available at: https://www.epa.gov/greenvehicles/fast-facts-transportation-greenhouse-gas-emissions

Smog, Soot, and Other Air Pollution from Transportation. EPA. Available at: https://www.epa.gov/transportation-air-pollution-and-climate-change/smog-soot-and-local-air-pollution

US Energy Information Administration – EIA – independent statistics and analysis. Electricity and the environment – US Energy Information Administration (EIA). Available at: https://www.eia.gov/energyexplained/electricity/electricity-and-the-environment.php

Vehicles, air pollution, and human health. Union of Concerned Scientists. Available at: https://www.ucsusa.org/resources/vehicles-air-pollution-human-health

How do humans cause pollution?