Google Advanced SearchCan be used to focus searches on specific file types, such as Excel, and Internet domains, such as .ca.gov for California government agencies or .edu for accredited education institutions in the USA. (For more on domains, see: https://www.pcmag.com/encyclopedia/term/internet-domain-name.) Can also be entered directly into basic Google search box, for example (for latest Excel file format):
pollution data site:.ca.gov filetype:xlsx
Caveat: just because a file is in Excel format does not mean it contains analyzable data.