RT Journal Article SR Electronic T1 Winter air pollution and respiratory function JF Occupational and Environmental Medicine JO Occup Environ Med FD BMJ Publishing Group Ltd SP 81 OP 81 DO 10.1136/oem.60.2.81 VO 60 IS 2 A1 M Lippmann YR 2003 UL http://oem.bmj.com/content/60/2/81.abstract AB