Air Pollution's Early Days In Los Angeles

Los Angeles has long been associated with smog and air pollution, which was once so thick it burned lungs and eyes and caused nausea. The city's air quality has improved dramatically over the last 30 years, but LA still has the worst ozone air pollution in the US, and the greater Los Angeles county contains 9 of the 15 most polluted cities in the country. So, when did LA's air pollution problem begin?

Los Angeles air quality

Los Angeles has long been associated with poor air quality, and the city is often known for its smog. The air pollution in LA was once so thick that it burned lungs and eyes and caused nausea. Schools were forced to close in the 1960s due to unsafe air quality, and outdoor activities like baseball games were frequently cancelled.

The smog is caused by a combination of PM2.5 and ozone. PM2.5 refers to airborne particulate matter measuring up to 2.5 microns in size, which is widely regarded as one of the most harmful pollutants due to its prevalence at dangerous levels. Ozone is a gas pollutant formed when sunlight reacts with nitrogen oxides and organic substances, which are both present in vehicle exhaust. As a result, traffic is frequently identified as a leading cause of LA's poor air quality. The summer months of June, July, and August tend to be more polluted due to drier conditions, less rainfall, higher temperatures, and a higher frequency of wind-blown dust and wildfires.

LA's air quality has improved dramatically over the last 30 years due to amendments to the Clean Air Act, as well as advancements in technology and the implementation of new policies. For example, from 2017 to 2018, LA's air pollution levels decreased by 10.6%, and they decreased by another 11.8% from 2018 to 2019. During the COVID-19 pandemic, lockdown measures resulted in an 18-day stretch of exceptionally clean air from March 7-28, 2020, the longest streak since at least 1995. Despite these improvements, LA still has a long way to go in the fight for clean air, as it remains one of the most air-polluted cities in the United States.

Causes of LA pollution

Los Angeles is known for its smog, which is caused by a combination of PM2.5 and ozone. The city's air pollution is among the worst in the United States, with 9 of the 15 most polluted cities in the country located within the greater Los Angeles county. While LA's air quality has improved over the last 30 years, it still doesn't meet the US EPA's national air quality standards for PM2.5 and ozone.

There are several causes of LA's pollution problem. Firstly, the city's geography and climate play a role. The summer months of June, July, and August tend to be more polluted due to drier conditions, less rainfall, higher temperatures, and a higher frequency of wind-blown dust and wildfires.

Secondly, human activities such as transportation and industrial processes contribute significantly to LA's air pollution. Vehicle exhaust is a major source of nitrogen oxides, which react with sunlight to form ground-level ozone, a harmful pollutant. In addition to cars, trucks, and buses, power plants and industrial facilities that burn fossil fuels are also major sources of nitrogen oxides and other pollutants like sulfur dioxide.

Another cause of LA's pollution is the presence of lead emissions from industrial processes like ore and metal processing, as well as non-road equipment that utilizes lead-containing fuel. Prolonged exposure to lead can have harmful effects on human health.

Agricultural practices, such as the use of chemical fertilizers and pesticides, as well as poor waste management, also contribute to air pollution in LA.

Wildfires, which can be naturally caused by lightning strikes, are another significant source of air pollution in the region. Wildfire smoke contains carbon dioxide, carbon monoxide, and fine particulates that pose health risks to humans and animals.

Health implications

Los Angeles has long struggled with air pollution, and the health implications of this are significant. The greater Los Angeles county contains 9 of the 15 most polluted cities in the United States, according to the 2019 World Air Quality Report. The city of Los Angeles ranked 82nd out of 1,517 US cities in that same report. Despite this seemingly positive ranking, the city's air pollution levels are among the worst in the country, especially for PM2.5 and ozone.

PM2.5 refers to airborne particulate matter measuring up to 2.5 microns in size. It is regarded as one of the most harmful pollutants due to its prevalence at dangerous levels. Exposure to PM2.5 has been linked to serious health issues such as heart disease, respiratory illness, coughing, breathing difficulties, chronic bronchitis, and premature death.

Ozone (O3), another critical pollutant, is a gas formed when sunlight reacts with nitrogen oxides and organic substances. Vehicle emissions, including cars, trucks, and buses, are significant sources of nitrogen oxides. Ozone levels tend to be higher during the summer months when sunlight is brightest, and it can cause a range of health issues. Exposure to ozone irritates and inflames the linings of the lungs, damaging lung function. This can lead to chest pain, coughing, throat irritation, congestion, and the exacerbation of lung diseases like asthma, bronchitis, and emphysema. Prolonged exposure to high ozone levels may even cause permanent lung tissue damage.

The health impacts of air pollution in Los Angeles are evident in studies like the Children's Health Study (CHS), which found reduced lung function growth, increased school absences, asthma exacerbation, and new-onset asthma at current pollution levels. According to the County of Los Angeles Public Health Department, 1 in 10 children have been diagnosed with asthma. Furthermore, the South Coast Air Quality Management District reports that overall cancer risk increases by 900 per million due to air pollution.

While Los Angeles has made strides in improving air quality over the past few decades, with notable reductions in pollution from 2017 to 2019, more aggressive efforts are needed to protect public health, especially that of children, who are particularly vulnerable to the effects of air pollution.

Progress made

Los Angeles has made significant progress in reducing air pollution over the last three decades. The Clean Air Act, amended in 1990, has been instrumental in improving the city's air quality. From 2017 to 2018, Los Angeles witnessed a 10.6% reduction in air pollution, followed by an additional 11.8% decrease from 2018 to 2019. The COVID-19 lockdown measures in 2020 further contributed to an 18-day stretch of exceptional air quality, the longest since 1995.

The transportation sector has been a key focus in the battle against air pollution. Electric vehicles and cleaner car engines have significantly reduced pollution from cars and trucks. However, heavy-duty trucks, cargo ships, and trains remain significant polluters. State and local regulators have implemented nation-leading rules to curb emissions from these sources, and efforts to modernise campuses have been initiated, although some plans have been delayed due to the discovery of dangerous vapours in the soil.

Los Angeles has also made strides in reducing pollution from industrial facilities. Increasing the use of renewable energy sources for the power grid is a critical step in this direction. Additionally, environmental advocates are working to uphold California's law preventing new oil and gas drilling near homes and schools.

While the city still faces challenges, particularly from extreme pollution events like wildfires, the overall trend is positive. The South Coast Air Quality Management District is actively discussing new rules to reduce pollution from Southern California's railyards and ports, and local regulations continue to drive progress. The long-standing improvements in air quality, coupled with promising new legislation and shifts in purchasing behaviour, provide optimism for the future of air quality in Los Angeles.

Comparison with other counties

Los Angeles is known for its smog, a combination of particle and ozone pollution. The greater Los Angeles county contains 9 of the 15 most polluted cities in the United States, according to the 2019 World Air Quality Report. In this same report, the city of Los Angeles ranked 82nd in the US out of 1,517 included cities. Its annual average differed by only 4 micrograms from the most polluted city in the US: Portola, California.

Los Angeles has the worst ozone air pollution in the United States, according to the 2019 State of the Air report, which compared data across 229 metropolitan areas. Ozone is a gas pollutant formed when sunlight reacts with nitrogen oxides and organic substances. Vehicle exhaust contains both the nitrogen oxides and reactive organic substances needed to form ozone, so traffic is frequently identified as a leading source.

Ozone pollution is not unique to Los Angeles, and nearly half of the people in the US live in areas where the air quality received an F in "State of the Air" 2025. More than 42 million people live in counties that received an F for all three air pollution measures.

The U.S. Environmental Protection Agency (U.S. EPA) has created a better indicator of air quality, the Air Quality Index (AQI). The AQI is calculated based on the levels of five major pollutants in the air: ground-level ozone, particle pollution, carbon monoxide, nitrogen dioxide, and sulfur dioxide. The AQI index runs from 0 to 500, with a higher number indicating greater air pollution. When the AQI for ozone rises above 150, children and older adults, as well as people with lung disease, are cautioned to reduce prolonged or heavy exertion outdoors.

Los Angeles air quality averages a US AQI rating of "moderate", with monthly averages in 2019 varying from AQI 32 ("good") in February to AQI 64 ("moderate") in November. Despite these seemingly optimistic ratings, Los Angeles's air pollution is among the worst in the United States, especially for PM2.5 and ozone. PM2.5 is airborne particulate matter measuring up to 2.5 microns in size, and is widely regarded as one of the most harmful pollutants to human health. Exposure to PM2.5 has been linked to heart disease, respiratory illness, and premature death.

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