• Background: Recent studies have linked exposure to airborne particulate matter (PM) to neurodevelopmental outcomes but the findings are mixed and mechanisms are unclear. We aim to determine the impact of PM on the developing brain of schoolchildren in Poland, a European country characterized by very high levels of air pollution. The investigators aim to determine the impact of PM on the developing brain of schoolchildren in Poland, a European country characterized by very high levels of air pollution.
• Study area: 19 towns in three voivodeships (Lesser Poland, Silesian, Opole) in the southern Poland. To reduce confounding by urbanicity and at the same time, to achieve sufficient contrasts in PM levels without too high logistic costs, towns were selected by size (big and small) and by PM levels (high, medium and low).
• Design: Case-control study with 800 children recruited over two school years, with two population controls per one ADHD case. Suspected cases will be recruited in specialized facilities and presumably ADHD-free children will be recruited in primary schools.
• Exposure assessment: Poland-wide PM and other air pollutants' grids will be created for the years 2006 to 2021 using statistical models to incorporate land use data, estimates from transport models, satellite observations and air pollution measurements from Polish monitoring network. Prenatal, early-life, lifelong and concurrent exposures will be calculated.
• Psychological testing: Every child and their parents will complete a series of psychological tests and interviews that will be conducted during their three visits to the recruitment facility.
• Neuroimaging: Each participant will undergo a Magnetic Resonance Imaging (MRI) scanning session that will be performed accordingly to the Human Connectome Adolescent Brain Cognitive Development project recommendations. Scanning will be performed on a single scanner in Krakow.

Inclusion Criteria:

• Attending school in one of the specified towns
• Age 10-13 years (4th-6th grade)
• Native Polish speaker
• Normal or above intelligence
• Standard educational opportunities
• Normal or corrected to normal visual and auditory acuity
• No gross sensory deficit, no gross behavioural problems
• No history of neurological disease

Exclusion Criteria:

• Autism spectrum disorder (ASD)
• FAS
• FAE
• Intellectual disability
• Metabolic disorders
• Genetic disorders
• Epilepsy
• Cerebral palsy
• Mood disorders
• Tourette Syndrome
• Other illnesses including pharmacotherapy
• Apgar score < 8
• Low birth weight (below 2500 g)
• Preterm birth (below 35th weeks of gestation)

800 children aged 10-13 will be sampled to the NeuroSmog study. Both ADHD cases and population controls will be enrolled, two control per case. Cases will be recruited in specialized facilities and controls will be randomly sampled in randomly selected 30 primary schools across 19 big and small towns in Lesser Poland, Silesian and Opole voivodeships in the southern Poland.