Development of mass spectroscopic technique for nitric acid measurements

为了准确测量硝酸，需要建立一种可靠的校准方法。为此，我们从40℃加热的渗透管中产生HNO3蒸汽，然后将其与零空气混合，引入总反应氮(NOY)检测器。从NOY信号中确定了HNO3的混合比例。此外，硝酸的生成率与NOY数据估计的一致，在10%以内。当含有硝酸的空气被引入硝酸测量系统的入口时，显著的滞后持续了20分钟以上。通过减小进样管的长度，观察到了显著的改善。当空气中的HNO3混合比例为0.1-10 ppbv时，观察到HNO3信号，大致与HNO3混合比例成正比。然而，即使在没有添加HNO3的情况下，也观察到对应于0.05-0.1 ppbv的HNO3信号。这一信号被解释为由于HNO3从质谱学系统的壁上释放出来。这表明为了测量高时间分辨率的HNO3，抑制背景信号是很重要的。

In order to measure nitric acid (HNO3) accurately, we need to establish a reliable method of calibration. For this purpose, we generated HNO3 vapor from permeation tube heated at 40 C.It was then mixed with zero air to be introduced into total reactive nitrogen (NOy) detector. HNO3 mixing ratios were determined from the NOy signals. In addition, the rate of HNO3 generation agreed with that estimated from the NOy data to within 10 %. When the air containing HNO3 was introduced into the inlet of HNO3 measuring system, significant hysterisis continued for over 20 minutes. Bu reducing the length of the inlet tube, significant improvement was observed.When air with HNO3 mixing ratios of 0.1-10 ppbv was introduced into the mass spectrometric system, HNO3 signals were observed, roughly proportional to the HNO3 mixing ratios. However, HNO3 signals corresponding to 0.05-0.1 ppbv were observed even in the case where no HNO3 was added. This signal is interpreted to be due to the release of HNO3 from the wall of the mass spectrometric system. This shows that it is important to suppress the background signals in order to measure HNO3 with high temporal resolutions.