1. Chemical Sciences Division, NOAA Earth System Research Laboratory; Boulder Colorado USA
2. Department of Chemistry and Biochemistry; University of Colorado Boulder; Boulder Colorado USA
3. Cooperative Institute for Research in Environmental Sciences; University of Colorado Boulder; Boulder Colorado USA
4. Department of Civil and Environmental Engineering; Hong Kong Polytechnic University; Hong Kong China
5. Department of Chemistry; University of California; Irvine California USA
6. PTC International Limited; Hong Kong China