The main purpose of EGR is to REDUCE combustion temperatures by mixture dilution which reduces the various oxides of Nitrogen production, commonly known as NOX, such as Nitrogen Dioxide… i.e. gases that kill living things. A quick search gives the following

Nitrogen oxides (NOx) harm life by causing respiratory and heart problems in humans, leading to lung irritation, asthma attacks, and increased mortality, especially in vulnerable populations. Environmentally, NOx contributes to the formation of photochemical smog and acid rain, damaging vegetation, reducing crop yields, altering soil chemistry, and affecting biodiversity in sensitive ecosystems. Some NOx, like nitrous oxide (N₂O), also act as a greenhouse gas and can induce short-term euphoria, but inhaling it in high concentrations is dangerous.

Effects on Human Health

  • Respiratory Issues:
    Inhaling NOx can irritate and inflame the respiratory tract, leading to coughing, shortness of breath, and an increased susceptibility to respiratory infections like pneumonia and bronchitis.
  • Aggravation of Existing Conditions:
    People with asthma or heart disease are particularly vulnerable to the adverse effects of NOx, which can trigger or worsen asthma attacks and increase mortality from cardiovascular and respiratory diseases.
  • Severe Symptoms:
    High-level exposure can cause serious symptoms such as pulmonary edema (fluid in the lungs), chemical burns on skin and eyes, and, in extreme cases, a life-threatening situation due to inadequate oxygenation of body tissues.
  • Mortality Risk:
    Long-term exposure to NOx is associated with an increased risk of all-cause mortality, as well as deaths from cardiovascular, respiratory, and non-accidental causes.

Environmental Effects

  • Photochemical Smog:
    NOx reacts with sunlight and hydrocarbons to form smog, which reduces visibility and has the same irritating health effects as NOx.
  • Acid Rain:
    NOx contributes to the formation of acid rain, which can damage vegetation, reduce crop yields, and alter the chemistry of soil and water bodies.
  • Ecosystem Damage:
    Deposition of nitrogen from NOx can change soil chemistry, leading to shifts in plant communities and negatively impacting biodiversity in sensitive habitats.

Other Effects

  • Nitrous Oxide: While other NOx are harmful pollutants, nitrous oxide (N₂O) is also a powerful greenhouse gas. Although used for medical purposes to induce a calm state, inhaling N₂O in high concentrations can cause serious health problems, including impaired cognitive function, nerve damage, and blood clots.