Several new developments associated with the sensitive Luminox NO2 monitor (the LMA-3) are presented: (1) A peroxyacetyl nitrate (PAN) converter has been developed for use with the LMA-3. It achieves a 3-sigma detection limit of 30 parts per trillion (ppt) with a time cycle of 5 min, which allows measurements in even clean background air. It is presently being commercialized with an integral Luminox detector. (2) A second converter/sequencer for NOx (NOx = NO2 + NO) and NO2 is described. It uses CrO3 for the NO conversion and presents significant advantages over the competitive commercial NOx detectors presently available, namely, sensitivity down to 10 ppt or less, and virtual freedom from interferences that now plague other methods. (3) An ozone scrubber has been developed that removes ozone (O3) from the sample air without destroying more than 10% of the NO2. This removes the major interference associated with the luminol method for NO2 measurements. Finally, the nonlinearities outside of the 1 to 50 ppb range have been characterized. An algorithm is presented for making corrections to ambient measurements, not only for nonlinearities but for residual ozone and PAN interferences. Typical atmospheric measurements (PAN, NO2, NOx, and O3) are given both for clean background air and for urban air in Long Beach, California.