1A: Neurotoxicity and Neuroinflammation by Air Pollution. Components of air pollution reach the brain either through the blood stream and/or through olfactory mucosa. Once in the brain, some moieties are neurotoxic and cause neuroinflammation. 1B: The Air Pollution-Lung-Brain Connection. Air pollution induces pulmonary and systemic inflammation, which induces CNS inflammation. 1C: Air Pollution and Gut α-Syn. Air pollution causes gut inflammation and leakiness, which promotes local accumulation of α-syn. α-Syn (white) can then spread to the brainstem via the vagus nerve (enlarged). 1D: Air Pollution, the Microbiome, and the Brain. Air pollution alters gut microbiome (enlarged), which can lead to systemic inflammation, release of neuroactive molecules and neuroinflammation.