Increasing awareness of the adverse health effects of air pollution leads to a demand of low-cost sensors for the measurement of pollutants such as NO₂. However, commercially available low-cost sensors lack accuracy and long-term stability, and suffer from cross-sensitivity to other gases. These drawbacks can be overcome by the method of quartz-enhanced photoacoustic spectroscopy (QEPAS). In QEPAS modulated light is absorbed by the NO₂ molecules, which results in the production of a sound wave. The sound wave is detected by resonance of a quartz tuning fork, which results in a measurable electric signal. Due to the small size of the tuning forks, the gas sensing element can be smaller than 1 cm³. We present the first bare fork QEPAS setup for the ppb-level detection of NO₂, which is ideally suited for environmental trace gas detection without the need of using micro-resonators. Micro-resonators are commonly used to amplify photoacoustic signals. However, micro-resonators have different dependencies on environmental conditions than tuning forks, which makes them difficult to operate in changing conditions. In contrast, our bare fork QEPAS setup is more robust and easily adopted by the use of a low-cost temperature and humidity sensor. By using acoustic filters the integration time could be increased to offer higher sensitivity at a continuous flow rate of 200 std cm³ min⁻¹. The 1σ noise equivalent concentration is determined to 21 ppb NO₂ in synthetic air for 120 s measurement time, allowing detection which satisfies international health and safety standards thresholds.

对空气污染对健康的不利影响的认识不断提高，因此需要用于测量污染物（如NO _2）的低成本传感器。但是，市售的低成本传感器缺乏准确性和长期稳定性，并且对其他气体具有交叉敏感性。这些缺点可以通过石英增强光声光谱法（QEPAS）克服。在QEPAS中，调制的光被NO ₂分子吸收，从而产生声波。通过石英音叉的共振来检测声波，从而产生可测量的电信号。由于音叉的尺寸很小，气体感应元件可以小于1 cm ³。我们展示了第一个用于NO ₂ ppb级检测的裸叉QEPAS装置，该装置非常适用于环境微量气体检测，而无需使用微谐振器。微谐振器通常用于放大光声信号。但是，微谐振器对环境条件的依赖性不同于音叉，这使得它们在变化的条件下难以操作。相比之下，通过使用低成本的温度和湿度传感器，我们的裸叉QEPAS设置更加坚固并且易于采用。通过使用声学滤波器，可以增加积分时间，以在200 std cm ³  min ^-1的连续流速下提供更高的灵敏度。1个σ在120 s的测量时间内，合成空气中的噪声当量浓度被确定为21 ppb NO ₂，可以进行检测，从而满足国际健康和安全标准阈值。