Open-path cavity ring-down spectroscopy sensor for atmospheric ammonia

Abstract

eutrophication and acidification of soils which lead to forest extinction and decline in biological diversity [3,4]. Ammonia also readily reacts with atmospheric species such as sulfuric acid (H 2 SO 4 ), nitric acid (HNO 3 ), and hydrochloric acid (HCl) to form fine particulate matter (PM 2.5 ) which can have harmful effects on human health [5]. The particles also cause haze which lead to visibility reduction and affect global radiation budgets [6][7][8]. Two major sources of ammonia are emissions resulting from domestic animals, and from motor vehicle combustion, meaning that most of the ammonia emitted to the atmosphere is directly or indirectly anthropogenic [9]. In spite of the importance of ammonia in the atmosphere, measurement of atmospheric ammonia concentrations and its regional variations have been relatively limited due to two important reasons:(1) Ambient concentrations are low and vary widely, and (2) ammonia is a sticky gas that introduces significant inlet challenges for typical closed-path instruments [8,10,11].We are primarily interested in ammonia emissions from concentrated animal feeding operations (CAFOs), such as feedlots and dairies, and in particular we seek to develop sensors for study of ammonia emissions and bidirectional fluxes and deposition [12,13]. Key sensor requirements are ppb level precision, and time response on the order of seconds, in order to measure turbulent (near-field) plumes that have concentrations typically ranging from 10 to 100 s of ppb. As will be discussed herein, widely used closedpath ammonia laser sensors typically have time response of ~30 s. While adequate for some applications, improving the time response to ~1 s would greatly benefit applications including: (1) moving toward widely used eddy-covariance methods that provide flux information [14], (2) quantifying fluxes from high emission transient/episodic events lasting for seconds to 10 s of seconds, e.g., manure handling/application, barn flushouts at dairies, and top dress application Abstract An open-path cavity ring-down spectroscopy (CRDS) sensor has been developed for measurement of atmospheric ammonia (NH 3 ) and represents the first use of open-path CRDS in the mid-infrared region. The sensor uses a continuous-wave distributed feedback quantum cascade laser at 10.33 μm to target strong absorption features. The optical cavity is constructed with two high-reflectivity mirrors (R = 0.9995). The open-path configuration removes inlet effects, which are very challenging for closed-path instruments, and can be enabling for compact, low-power designs. Sensor performance was validated in the laboratory by measuring known concentrations in a closed-path configuration. The open-path configuration was validated by comparison against a commercial closed-path CRDS instrument for outdoor measurements at a small feed lot. Ammonia concentrations from the two instruments showed good agreement with slope of 0.990 (R 2 = 0.92), for 5-min averages. The precision of the open-path instrument was found from Allan varianc...

Optical field propagation model of ring-down cavity light field based on angular spectrum propagation theory and evaluation criterion of cavity tuning

“…透射光强峰值一般为衰荡信号的峰值, 反映注 入光束在谐振腔内的能量耦合效率, 至今仍在光腔 衰荡技术中广泛使用. 文献 [19,20] 束干涉叠加理论 [16,25,26] 接下来分析E 0 在腔内往复传输过程和衰荡过 程. 首先根据角谱传播理论 [27] 计算初始光场传输 到达腔镜M 2 的光场分布E 1 , 则:…”

A talaj ammónia kibocsátásából adódó környezetterhelés és annak monitorozási, mérési lehetőségei

“…Egy másik spektroszkópiai eljárás, az üregrezonátoros lecsengési spektrometria (CRDS) (SHADMAN et al, 2016). Ennek során egy adott hullámhosszúságú, a sugárforrásból szakaszosan kibocsátott fénysugár nagy utat tesz meg a mintázni kívánt gázon át egy tükörrendszerrel szerelt cellában, a tükrök között nagy számban vissza verődve.…”

Dynamic ammonia measurement based on quantum cascade laser absorption spectroscopy

“…The main detection techniques commonly used in laser spectroscopy include cavity ring-down spectroscopy (CRDS) technology, quartz-enhanced photoacoustic spectroscopy (QEPAS) technology, and tunable diode laser absorption spectroscopy (TDLAS) technology. CRDS technology relies on a highly precise optical cavity consisting of highly reflective mirrors, achieving a long optical path length and excellent sensitivity 13 . Gadedjisso-Tossou et al 14 .…”

“…CRDS technology relies on a highly precise optical cavity consisting of highly reflective mirrors, achieving a long optical path length and excellent sensitivity. 13 Gadedjisso-Tossou et al 14 developed a CRDS sensor for the detection of trace NH 3 for the spectral line at 1470.58 cm −1 , obtaining a sensitivity of 9 ppb. Unfortunately, the system has poor adaptability to the environment, requiring frequent calibration of the system and abnormally difficult adjustment of the optical path.…”