Air quality monitoring is gaining importance in public health due to the increasing level of the pollution in cities. In addition, people are more concerned about their personal exposure and they are interested to know the concentration levels of the pollutants, which surround them. In recent years, wearable technology can be useful for continuous air quality monitoring when people are moving in urban and industrial environments. As wearable systems are usually battery-powered and gas sensors are power-hungry, energy-efficient design and power management are required. In this paper, we present a two-stage gas sensing concept where novel multiple-Single-Walled Carbon Nanotubes (SWCNT) are proposed as detectors for an energy-hungry metal-oxide (MOX) semiconductor gas sensor. We simulate the system performance combining the low power consumption of SWCNT gas sensors and the more mature MOX sensor to achieve an energy-efficient wearable device able to monitor the air quality continuously while achieving long lifetime. We perform simulations using measured power consumptions for two event-driven scenarios to evaluate the power consumption reduction and lifetime extension in a wearable mobile context. Our results show that the proposed approach prolongs node lifetimes by 30 times compared to adaptive duty-cycling with only MOX gas sensors. We also propose that the nanotube recovery time issue can be overcome by using four single nanotubes on the same chip, which results in an extension of lifetime.