A monitoring system may include a server, and mask devices in communication with the server. Each mask device may include a mask body to be worn by a respective user, an air quality sensor carried by the mask body and configured to detect a contaminant concentration value in air breathed through the mask body, a wireless transceiver carried by the mask body and in communication with the server via a wireless link, and a processor carried by the mask body and coupled to the air quality sensor and the wireless transceiver. The processor may be configured to send an alert message to the server when the contaminant concentration value respectively exceeds a threshold.