A method and apparatus for an inline air purification system is described herein. An example apparatus includes a housing, a high-velocity air flow guide, a filter assembly, and a fan. The high-velocity air flow guide includes a first portion and a second portion. The first portion is configured to form a passage within the housing, and the second portion is configured to divert and accelerate air flow of the ambient air from the passage to a chamber of the housing. The filter assembly includes one or more filtering elements configured to receive the ambient air from the chamber. The fan is configured to draw the ambient air from the chamber through the filter assembly and to generate processed air from the ambient air. The housing is located in an HVAC duct, and occupies only part of the cross-sectional area of the duct. The remaining area of the duct accommodates bypass air flow to a primary fan in the HVAC system.