3.1.2. Cavity supported optical absorption spectroscopy –CRDS and CEAS

An overview of cavity supported absorption spectroscopic techniquesfor atmospheric trace gases is given by Ball and Jones (2003)and Brown et al. (2003). Cavity ring down spectroscopy (CRDS) was developed by O’Keefe (Scherer et al., 1997) and is a highly sensitive form of laser absorption spectroscopy that in recent years has proved useful for measurements of stable compounds aswell as radicals and aerosol extinction in ambient atmosphere and laboratory experiments.The centrepiece of the CRDS technique is a high quality  (reflectivity of the mirrors >99.99%), two-mirror stable resonator  into which pulsed laser light is injected through one end mirror. This  mirror reflects most of the incident light but a small fraction couples into the cavity and decays (‘rings down’) exponentially in time, with the time decay – in the empty cavity – mainly determined by the mirror losses. When an absorbing compound is introduced into the cavity and the laser is tuned to an absorption resonance, the losses rise and the ring down time is reduced. From the reduction in the time constant, the number density of the absorbing species can be  determined directly. This detection principle has the big advantage  of being insensitive to intensity fluctuations of the light source. The  zero ring downsignal is achieved by measurement of the sample gas without the absorbing species, e.g. for NO3 radical measurements after chemical titration of NO3 with NO added into the detection cell (chemical modulation technique). The technique needs no in-field calibration. With state-of-the-art mirrors and laser sources absorption signals in the 10

11 cm

1 range can be detected with 1 s time resolution. Examples of its applications in ambient measurements are exemplified below; for applications in kinetic studies, see Section 3.3.1.

3.1.2 腔支持光吸收谱 –CRDS 和 CEAS

Ball ，Jones (2003) 和Brown (2003) 等，给出了腔的综述支持腔吸收大气示踪气体光谱技术。 由 O'Keefe （Scherer et al.，1997年) 开发的腔环倒谱 (CRDS)是一种高度敏感，近年来已证明能用于测量稳定的化合物，以及自由基与周围的气氛和实验室实验中的气溶胶消光。中心片中是一个高质量 (反射率的镜像 > 99.99%），一端镜像通过注入两个镜像稳定谐振器的脉冲激光光。此镜像反映了大部分的入射光，但一小部分光在腔内和衰变 ('环下') 的指数，随着时间的衰变变为空腔，主要由镜像损失的部分决定。 当一个吸收复合腔引入时，激光调到一个吸收共振损失上升，减少停机时间环。 从时间常数有所减少的吸收的物种数密度可以直接确定。 此检测原理的大优势在于它对光源的强度变化不敏感。零环下信号被通过不吸收的物种比如 NO3 自由基测量后化学滴定法与 NO NO3 添加到该检测单元格 （化学调制技术） 的情况下，示例气体测量。技术不需要现场校准。 激光与先进的镜像源吸收10 -11 厘米范围内的信号可以检测 1 s 时间分辨率。 其环境测量中的应用程序的示例如下； 动力学研究中的应用程序，请参阅第 3.3.1。

3.1.1. Mass spectrometric analytical techniques

The principle of mass spectrometry using ionisation methods at atmospheric pressure (API) has enormously increased the analytical power of mass spectrometry. In particular the atmospheric pressure chemical ionisation (APCI) and the electrospray ionisation (ESI)  methods are nowwidely used in routine analysis (see also section on PTR-MS and HOx radicals below). ESI and APCI are highly efficient for polar compounds in either the positive or negative ion mode. For non-polar compounds atmospheric pressure photo ionisation (APPI)  provides an alternativemethod (Syage et al.,2000). These techniques are based on the ionisation with a single UV photon with a wavelength of l?123.8nm(10 eV). Atmospheric pressure laser ionisation  (APLI) (Constapel et al., 2005) is the youngest technique among the variety of ionisation methods operating at ambient pressure. APLI uses resonant enhanced mulitphoton ionisation (REMPI).

3.1.1 质谱分析技术

大气压 (API) 方法电离质谱法的原则极大地增加了的质谱分析的能力。 尤其大气压化学电离 (APCI) 和电喷雾电离 (ESI) 方法现在广泛应用于常规分析（请参见PTR 和 HOx 下有关基础）。 高效正面或负面的离子模式中极性化合物的电喷雾和 APCI。 非极性化合物大气压力的照片电离 (APPI) 提供了一种替代方法 (Syage et al.，2000年)。 这些技术基于 l？123.8nm(10 eV) 的波长与一个单紫外光子电离。 常压激光电离 (APLI) (Constapel et al.，2005年) 是在环境压力下各种电离方法中{zx1}的技术。 APLI 使用共振增强的叠加光子电离 (REMPI)。