Background Ambient airborne particulate material (PM) is defined according the aerodynamic diameter into coarse, fine, and ultrafine or "nano" sized particles ranging between 2.5-10 µm (coarse), <2.5 µm (fine), and <0.1 µm (nano(. Many studies have examined particle effect on respiratory health in children, mainly by environmental monitoring of coarse and fine particles. Biological assessment of individual exposure to nano sized particles in correlation to adverse health effect was not previously studied.

Hypothesis individual exposure to nano sized particles in children is associated with reduction in forced expiratory volume at one second.

Inclusion Criteria:

• age 6-18 years
• living in the Tel Aviv area
• referred to the pulmonology lab for respiratory function evaluation

Exclusion Criteria:

• Exposure to cigarette smoke
• Respiratory infection in the 4 weeks prior to recruitment and testing

asthmatic and control children