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<p>The Portable (2.7 kg) Cavity-enhanced Absorption of Nitrogen Dioxide (PCAND) instrument for measuring in situ nitrogen dioxide (<span class="inline-formula">NO₂</span>) was developed using incoherent broadband cavity-enhanced absorption spectroscopy (IBBCEAS). An LED light source centered at 408 nm was coupled to a cavity 15 cm in length, achieving an effective optical pathlength of <span class="inline-formula">∼520</span> m. Precision was measured as 94 pptv (1 s). To date, we have flown this instrument on three balloon test flights. This instrument records data on an SD card and outputs data (via an RS232 port) to external devices including a commercial radiosonde (iMet) for real-time data downlink.</p>