Concerns about the health effects of nitrogen dioxide ( ${\mathrm{NO}}_2$ ) and its role in forming deleterious atmospheric species have made it desirable to have low-cost, sensitive ambient measurements of ${\mathrm{NO}}_2$ . We have developed a continuous-wave laser-diode laser-induced fluorescence (LIF) system for ${\mathrm{NO}}_2$ that operates at ambient pressure, thereby eliminating the need for an expensive pumping system. The current prototype system has achieved sensitivity several orders of magnitude beyond previous efforts at ambient pressure (limit of detection of $2\mathrm{ppb}$ , $60\mathrm{s}$ averaging time). Ambient measurements of ${\mathrm{NO}}_2$ were made in Portland, Oregon using both the standard ${\mathrm{NO}}_2$ chemiluminescence method and the LIF instrument and showed good agreement ( $r^2=0.92$ ).