Air pollution is a global problem affecting millions of people’s health and well-being. It is a complex issue that has far-reaching effects on the environment and human health. According to a report by the Lancet Commission on pollution and health, in 2019, air pollution was the leading environmental cause of disease and premature death worldwide, resulting in 6.7 million casualties. In India, air pollution led to more than 1.67 million premature deaths during the same period, constituting 25 percent of global deaths. The primary air pollutants that impact human health include nitrogen oxides (NOx), sulphur oxides (SOx), ozone, and particulate matter (PM). PM below 2.5 microns is of particular concern because it can penetrate deep into the lungs and affect both the respiratory and vascular systems, brain function and cerebral circulation. The sources of PM 2.5 vary depending on location but can include vehicle emissions, industrial processes, and burning fossil fuels for energy. The severity of the health effects depends on the exposure level and duration. Therefore, it is indisputable that air pollution severely affects public health.
Violence is also a significant cause of death worldwide. According to the World Health Organisation, injuries – both unintentional and violence-related – take the lives of 4.4 million people around the world each year and constitute nearly eight percent of all deaths. Therefore violence is also a public health and safety issue. As a social and behavioural science researcher, I am curious in exploring the potential link between air pollution and violent crime. This blog is my attempt to find an answer.
Locating the nexus between air pollution and violent crime
The effects of air pollution on the respiratory and circulatory systems are well known. We now have increasing evidence that air pollution can have a significant impact on the Central Nervous System (CNS) too. Violence is a complex and heterogeneous behaviour that is underpinned by various parts of the CNS (apart from social, cultural and economic factors). We know that various parts of the brain work together to keep human responses to external stimuli, safe and socially appropriate; the amygdala (by shaping the responses to emotional stimuli), the limbic prefrontal cortex (by assessing the value of a stimulus and determining a response to it), the striatum (by moderating reactivity to provocations), the neurotransmitter serotonin-dopamine mechanism (by having an inhibitory effect on the brain). Any interruptions to these complex mechanisms can potentially contribute to violent behaviour.
The mechanisms by which pollutants can alter brain function are also diverse and complex. It could range from direct injury to the white matter (the millions of nerve fibres that connect the different regions of the brain) to indirect effects such as the alterations to cardiovascular, pulmonary and immune systems which then affect the CNS.
The routes of toxicity are also varied. While inhalation of polluted air results in a complex set of compounds directly reaching the brain, there are also other exposure routes. For example, the gastrointestinal route by the ingestion of food and drink contaminated by air pollutants through the microbiome-gut-brain axis or via dermal (skin) contact are less well known, but are being explored as potential routes of neurotoxicity.
It is no surprise then that the effects of air pollution on the brain is also diverse. Poor air quality has been implicated in the expression of neurodevelopmental conditions such as autism, and degenerative conditions such as Alzheimers; poor air quality has been linked with cognition, memory and learning deficits especially when young, developing brains are exposed to it; poorer air quality could possibly contribute to social behaviour alterations of different types - for example, more delinquent behaviour from boys (though this should be considered as a factor together with other concomitant emotional and social stressors); poor air quality can potentially increase the risk of clinical depression (which incidentally is linked to an increase in violent behaviour).
Keeping these complex and myriad factors in mind, we will now consider a few studies that look at the correlation between poor air quality and the incidence of violence.
A study conducted in 34 states over 13 years (2000-2013) in the USA using daily monitoring data for ozone and PM 2.5 found that ambient air pollution may be associated with an increased risk of violent behaviour. Another study combined data on crime, pollution, wildfire smoke and weather to create a dataset covering the continental United States from 2006 to 2013. The results suggest a positive effect of increased air pollution on violent crimes and, specifically, assaults. The study also found that reducing air pollution could save $1.4 billion (≈ ₹11,500 crores) in crime costs per year. These costs are not included in cost-benefit analyses of air pollution, leading to an underestimation of the need for effective air quality regulation.
Apart from linking ozone and PM 2.5 concentrations to crime, some researchers also studied the effects of carbon monoxide emissions on the degree of physical violence exhibited by an offender in the United States. The study found that carbon monoxide emissions have little effect on the overall level of physical violence displayed by a criminal offender. However, the offender’s race and gender affect the relationship between air pollution and victim injury. As carbon monoxide levels increase in a city, black and male offenders are more likely to injure their victims physically. According to the researchers, black and male offenders are more susceptible to the effects of air pollution that can induce violence due to notable disparities in carbon monoxide exposure based on race and gender. One more study examined the effects of air pollution on assault rates in 204 police districts in South Korea from 2001 to 2018. The results showed that ozone increased assaults locally and regionally, and nitrogen dioxide increased assault rates in surrounding areas.
Some researchers in Russia have studied the effects of air pollution from transportation, on criminal behaviour. It explores theories on childhood lead exposure and its impact on violent crime rates and questions whether the ban on leaded gasoline affected violent crime in some regions. The regions being discussed have a moderate homicide rate compared to the rest of the country. However, the rate of intentional serious bodily harm in these regions is still relatively high. Thus, this study also established a relationship between air pollution and violent crime. The researchers' further caution that though environmental factors are an important contributing factor to violent crime, this should be studied in a complex and systematic way with other factors like unemployment, low financial security, alcoholism, etc.
Overall, these studies suggest a complex relationship between air pollution and violent criminal behaviour and highlight the need for further research to fully understand the mechanisms underlying this association. Nevertheless, the findings have important implications for public health and policy. Governments and policymakers must consider the potential costs of air pollution on crime when considering air quality regulations and mitigation strategies, which are always overlooked. Moreover, the results emphasise the need for a multi-sectoral approach that addresses not only environmental factors but also socioeconomic and cultural factors contributing to violent criminal behaviour.
By taking a comprehensive approach, it is possible to reduce the negative impacts of air pollution on public health and human safety, ultimately improving the overall quality of life. Collaborative efforts and inter-agency cooperation between different environmental law enforcement agencies, including state pollution control boards and the police department, are crucial to address this pertinent problem. There should be active measures to address air pollution and violent crime at both city and inter-city levels and exchange of information on air pollution and crime between cities and regions as a collaborative response. Governments can also take steps to reduce air pollution by implementing policies to reduce emissions from factories, fossil fuel-based power plants, and vehicles. In addition to existing measures, more comprehensive policy actions are needed to effectively reduce air pollution. This can include revising regulations on vehicle emissions standards to be more stringent, promoting the use of cleaner energy production methods such as renewable energy sources, and implementing urban planning strategies that encourage walkability and the use of public transportation. These broader policy measures can help address the limitations of current policies in tackling air pollution. As individuals, we can take steps to reduce our contribution to air pollution, such as driving less and using public transportation, using energy-efficient appliances, etc. In conclusion, reducing air pollution is important for our physical and mental health and personal safety. Let us all do our part in reducing air pollution and creating a cleaner, healthier environment for ourselves and future generations.