The Smog Problem: How Did La Get Here?

Los Angeles, California, is known for its smog, a combination of particle and ozone pollution. While air quality has improved over the last three decades, LA still does not meet the U.S. EPA's national air quality standards for ozone. The LA-Long Beach metropolitan area has been ranked as having the worst ozone pollution in the nation. So, how did this happen?

Vehicle emissions

Los Angeles, California, has long been known for its poor air quality, specifically its ozone pollution. The LA-Long Beach metropolitan area has been ranked as having the worst ozone pollution in the nation. While air quality has improved over the last few decades, 98% of Californians still live in areas with unhealthy levels of smog and fine particles.

Motor vehicles are the leading source of city-wide PM 2.5 and nitrogen dioxide, a precursor pollutant to ozone. Nitrogen oxides, emitted from vehicle exhaust, are a key component of smog and contribute to the formation of ozone pollution. While efforts have been made to reduce emissions from cars, the shift away from diesel-powered trucks, ships, and trains has proven challenging.

The Clean Air Act and its amendments have helped to reduce emissions and improve air quality. The shift towards electric vehicles and the use of renewable energy sources are also promising steps towards reducing vehicle emissions and improving LA's ozone pollution. However, despite these efforts, high-pollutant events still regularly exceed accepted thresholds, particularly on hot days.

Transportation emissions, including those from vehicles, are a major factor in LA's ozone pollution. While progress has been made, there is still a long way to go to ensure clean air and protect the health of Californians.

Wildfires

Research has shown that wildfires can significantly influence air quality. For example, wildfires in Canada in 2023 blanketed the Upper Midwest and East Coast in smoke, raising ozone and particle pollution levels in dozens of states to their highest levels in many years. Wildfires in California in 2020 caused downtown Los Angeles to record its highest ozone pollution in 26 years. During these periods, MDA8 O3 increased by an average of 6.5 ppb, with about 5.5 ppb (+10%) being attributable to the wildfires.

The impact of wildfires on ozone levels is particularly concerning given the adverse health effects associated with ozone exposure. Ozone is a secondary pollutant formed when precursor gases react with sunlight and can also warm the atmosphere. Breathing in ozone can cause immediate breathing problems like shortness of breath, wheezing, coughing, and an increased risk of respiratory infections. It can also cause damage to the tissues of the respiratory tract, leading to symptoms such as chest pain, emphysema, and asthma.

The role of wildfires in ozone formation highlights the complex nature of air pollution and the need to address it comprehensively. While regulations have limited NOx production by human-made sources, satellite data has shown rising NOx levels in remote areas of California due to wildfire activity. As such, wildfires are driving an increase in ground-level ozone pollution and contributing to a fundamental shift in the atmosphere's chemistry.

Industrial sources

Los Angeles has long been known for its smog, a combination of particle and ozone pollution. While the city's air quality has improved in recent years, it still does not meet the U.S. EPA's national standards for ozone and PM2.5. Industrial sources, including vehicle emissions, shipping, manufacturing, and wildfires, have all contributed to the city's ozone pollution.

Transportation and industrial emissions are major contributors to ozone pollution in Los Angeles. The burning of fossil fuels, especially by vehicles, ships, planes, and manufacturing processes, releases nitrogen oxides (NOx) and volatile organic compounds (VOCs), which are precursors to ozone formation. The large population of Los Angeles, with 4 million people in the city and another 6 million in the surrounding county, contributes to heavy vehicular emissions and traffic congestion. It is estimated that there are 6.5 million vehicles in the city alone, making motor vehicles the leading source of city-wide nitrogen dioxide, an ozone precursor pollutant.

In addition to road transportation, emissions from aircraft, locomotives, and oceangoing vessels also fall under federal jurisdiction and impact air quality in Los Angeles. The ports of LA and Long Beach are the largest fixed source of smog-forming emissions in the basin, producing an estimated 100 tons of smog daily. While efforts have been made to reduce emissions, such as investing in cleaner energy transport vehicles, there has been little year-over-year improvement since 2011.

While clean air policies and regulations have helped reduce ozone pollution in Los Angeles, the city continues to face challenges in meeting air quality standards. The shift towards electric vehicles and the increasing use of public transportation are positive steps towards reducing transportation emissions. Additionally, improving the power grid's reliance on renewable energy will be critical in reducing industrial emissions and improving Los Angeles' air quality.

Population

Los Angeles is a city notorious for its smog, a combination of particle and ozone pollution. The prevalence of these pollutants results from many factors, including the burning of fossil fuels, especially by vehicles, ships, planes, and manufacturing, as well as wildfires. The large population of 4 million in Los Angeles, with another 6 million in the surrounding Los Angeles county, contributes significantly to its poor air quality because of heavy vehicular emissions and traffic congestion. It is estimated that there are 6.5 million vehicles in the city of Los Angeles alone.

The LA-Long Beach metropolitan area continues to have the worst ozone pollution in the nation, according to the American Lung Association's State of the Air Report. The report also found that 38.5 million California residents live in a county that received a failing grade for air quality, with Los Angeles ranking first for the highest number of unhealthy ozone days since 2010. The large population of the city and its surrounding areas, therefore, play a significant role in the high levels of ozone pollution.

The high population density in Los Angeles leads to a high number of vehicles on the road, contributing to the city's poor air quality. While there have been efforts to reduce emissions, such as the Clean Air Act and the shift towards electric vehicles, the number of vehicles remains a significant source of pollution. The South Coast Air Quality Management District has also sued the U.S. Environmental Protection Agency, arguing that their policies have made it impossible to achieve clean air standards in the Los Angeles area.

The large population of Los Angeles also means that there is a high demand for energy, which can contribute to increased pollution levels. While there have been efforts to increase the percentage of the power grid that relies on renewable energy, the long-standing use of fossil fuels and the high energy demand of a large population can still impact air quality. Additionally, the large population of Los Angeles means that there is a high demand for goods and services, which can result in increased pollution from industrial sources and transportation emissions from trucks and shipping.

The impact of the population on ozone pollution in Los Angeles is evident in the data. While there have been improvements in air quality over the years, with a decline in aerosol concentrations and ozone levels, the high population density and associated emissions have led to a plateau in recent years. This suggests that while emission controls have targeted major sources of pollutants, the most prominent sources now may be those that are unaffected by current policies, such as the large number of vehicles in the city.

Temperature

Firstly, temperature interacts with various pollutants to form ozone. Nitrogen oxides (NOx) and volatile organic compounds (VOCs) are precursors to secondary organic aerosols (SOAs), which, in turn, are precursors to ozone formation. Research by Nussbaumer and Cohen has shown that SOA formation is highly temperature-dependent, and this effect, previously observed in rural areas, is now also evident in cities like Los Angeles. Thus, temperature influences the rate at which these precursors react to form ozone.

Secondly, temperature affects the dispersion and dilution of ozone and other pollutants. Warmer temperatures can cause an increase in atmospheric turbulence, which may enhance the dispersion of pollutants, including ozone, over a larger area. However, in certain meteorological conditions, such as temperature inversions, the atmosphere may trap ozone and other pollutants near the surface, leading to higher concentrations and poorer air quality.

Additionally, temperature influences the sources of ozone precursors. For example, transportation emissions, a significant contributor to nitrogen oxide emissions, are affected by temperature. Warmer temperatures can increase the use of air conditioning in vehicles, altering emission rates. Similarly, the operation of aircraft, locomotives, and oceangoing vessels, all of which emit nitrogen oxides, can be temperature-dependent, impacting ozone precursor emissions.

The temperature also plays a role in the frequency and intensity of wildfires, which contribute to ozone pollution in Los Angeles. As temperatures rise, the risk of wildfires increases due to drier conditions and more frequent droughts. Wildfires release a range of pollutants, including nitrogen oxides and volatile organic compounds, which contribute to ozone formation. Thus, the temperature-driven increase in wildfire activity can indirectly influence ozone levels.

Lastly, temperature can impact the effectiveness of emission control measures. Some technologies and strategies for reducing emissions may be more or less effective under different temperature conditions. For example, the implementation of measures to reduce vehicle emissions may be influenced by temperature-driven changes in transportation patterns, such as shifts in the use of air conditioning or public transportation.

In summary, temperature is a critical factor in the complex interplay of factors contributing to ozone pollution in Los Angeles. Its influence on precursor formation, atmospheric dispersion, emission sources, wildfire activity, and the effectiveness of control measures collectively shape the ozone pollution levels experienced by the city. Addressing ozone pollution requires a comprehensive understanding of these temperature-related factors and their dynamic interactions.

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