For an accurate assessment, a professional inspection is essential to determine the source of the moisture—likely condensation from a cold wall or a leak exacerbated by the rains—and the full extent of the spread. You cannot remediate mold without first fixing the moisture problem, or it will simply return.

Attempting a DIY removal on a large patch is strongly discouraged. Disturbing the mold without proper containment, such as during scrubbing, will aerosolize the spores and spread them throughout your apartment, potentially making the air quality worse. Professionals use physical barriers, negative air pressure machines, and HEPA filtration to prevent cross-contamination.

For a verified remediation, expect the process to involve identifying and rectifying the moisture source, containing the area, safely removing and disposing of contaminated porous materials like drywall, HEPA vacuuming, and antimicrobial treatment. The final, critical step is post-remediation verification (clearance testing) to confirm the spore count in the air has returned to acceptable levels.

Given the climate and potential health impact, the most reliable path is to get a detailed assessment from a company that can provide a scope of work and uses a third-party lab to verify the results.