Request for information: 

"Could you please provide an update on the progress of investigations into engineering solutions for improving air quality. Specifically, I would like to know: 

a) When did the investigation into engineering solutions begin, and what stage is it currently at? 

b) Have any potential engineering solutions been identified or evaluated? 

c) Are there any preliminary findings or insights from the investigation? 

d) Is there an estimated timeline for when the investigation will be complete and the engineering solutions implemented? 

e) Are there any plans to communicate updates or progress regarding air quality improvements to the public? 

Additionally, regarding the ventilation in trains, could you please provide information about the MERV grade of filtration used and the ventilation airflow rate in L/s per person at maximum capacity?"