Reorganize research narrative

[jinlx]

Summary

• reorganize the Research page into a source-to-receptor scientific progression
• move chemical-mechanism development next to fresh-smoke chemistry
• clarify the roles of OH exposure, photochemical age, and ozone isopleths
• strengthen transitions among emissions, chemistry, satellite analysis, and health applications
• preserve all existing research claims and related-work links

Why

The previous page contained the right topics, but their order did not fully communicate how Lixu Jin's work connects emissions at the source to chemistry, transport, exposure, and public health.

Impact

Readers can now follow one coherent research narrative:

1. emissions
2. fresh-smoke chemistry
3. chemical mechanisms
4. chemical aging
5. ozone-production regimes
6. satellite and model evaluation
7. community exposure and health

Validation

• reviewed the complete one-file revision
• checked heading order and Markdown formatting
• checked the diff for whitespace errors
• GitHub's Site checks workflow will perform the full Jekyll build and internal-link check