In the sentence extracted from biomedical literature, identify all the chemical entities. The required answer format is the same sentence with HTML <span> tags to mark up specific entities. 
### Entity Markup Guides:
Use <span class="chemical"> to denote a chemical.

### Input Text: Daily predicted pollutant concentrations were used to derive surrogates of long - term exposure and link them to study participants ' geocoded addresses .
### Output Text:
Daily predicted pollutant concentrations were used to derive surrogates of long - term exposure and link them to study participants ' geocoded addresses . 