This article presents a literature review of sensors for the monitoring of benzene in ambient air and other volatile organic compounds. Combined with information provided by stakeholders, manufacturers and literature, the review considers commercially available sensors, including PID-based sensors, semiconductor (resistive gas sensors) and portable on-line measuring devices as for example sensor arrays. The bibliographic collection includes the following topics: sensor description, field of application at fixed sites, indoor and ambient air monitoring, range of concentration levels and limit of detection in air, model descriptions of the phenomena involved in the sensor detection process, gaseous interference selectivity of sensors in complex VOC matrix, validation data in lab experiments and under field conditions.

After a series of seminal works during the last decade of the 20th century, nitric oxide (NO) is now firmly placed in the pantheon of plant signals. Nitric oxide acts in plant–microbe interactions, responses to abiotic stress, stomatal regulation and a range of developmental processes. By considering the recent advances in plant NO biology, this review will highlight certain key aspects that require further attention. The following questions will be considered. While cytosolic nitrate reductase is an important source of NO, the contributions of other mechanisms, including a poorly defined arginine oxidizing activity, need to be characterized at the molecular level. Other oxidative pathways utilizing polyamine and hydroxylamine also need further attention. Nitric oxide action is dependent on its concentration and spatial generation patterns. However, no single technology currently available is able to provide accurate in planta measurements of spatio-temporal patterns of NO production. It is also the case that pharmaceutical NO donors are used in studies, sometimes with little consideration of the kinetics of NO production. We here include in planta assessments of NO production from diethylamine nitric oxide, S-nitrosoglutathione and sodium nitroprusside following infiltration of tobacco leaves, which could aid workers in their experiments. Further, based on current data it is difficult to define a bespoke plant NO signalling pathway, but rather NO appears to act as a modifier of other signalling pathways. Thus, early reports that NO signalling involves cGMP—as in animal systems—require revisiting. Finally, as plants are exposed to NO from a number of external sources, investigations into the control of NO scavenging by such as non-symbiotic haemoglobins and other sinks for NO should feature more highly. By crystallizing these questions the authors encourage their resolution through the concerted efforts of the plant NO community.

We demonstrate a new technique for absolute distance measurement with a femtosecond frequency comb laser, based on unraveling the output of an interferometer to distinct comb modes with 1~GHz spacing. From the fringe patterns that are captured with a camera, a distance is derived by combining spectral and homodyne interferometry, exploiting about 9000 continuous wave lasers. This results in a measurement accuracy far within an optical fringe ($\lambda${}/30), combined with a large range of nonambiguity (15~cm). Our technique merges multiwavelength interferometry and spectral interferometry, within a single scheme.

• The results of a single publication stating that terrestrial plants emit methane has sparked a discussion in several scientific journals, but an independent test has not yet been performed. • Here it is shown, with the use of the stable isotope ¹³C and a laser-based measuring technique, that there is no evidence for substantial aerobic methane emission by terrestrial plants, maximally 0.3% (0.4 ng g⁻¹ h⁻¹) of the previously published values. • Data presented here indicate that the contribution of terrestrial plants to global methane emission is very small at best. • Therefore, a revision of carbon sequestration accounting practices based on the earlier reported contribution of methane from terrestrial vegetation is redundant.

Different forms of nitrogen (N) fertilizer affect disease development; however, this study investigated the effects of N forms on the hypersensitivity response (HR)—a pathogen-elicited cell death linked to resistance. HR-eliciting Pseudomonas syringae pv. phaseolicola was infiltrated into leaves of tobacco fed with either or . The speed of cell death was faster in -fed compared with -fed plants, which correlated, respectively, with increased and decreased resistance. Nitric oxide (NO) can be generated by nitrate reductase (NR) to influence the formation of the HR. NO generation was reduced in -fed plants where N assimilation bypassed the NR step. This was similar to that elicited by the disease-forming P. syringae pv. tabaci strain, further suggesting that resistance was compromised with feeding. PR1a is a biomarker for the defence signal salicylic acid (SA), and expression was reduced in -fed compared with fed plants at 24h after inoculation. This pattern correlated with actual SA measurements. Conversely, total amino acid, cytosolic and apoplastic glucose/fructose and sucrose were elevated in - treated plants. Gas chromatography/mass spectroscopy was used to characterize metabolic events following different N treatments. Following nutrition, polyamine biosynthesis was predominant, whilst after nutrition, flux appeared to be shifted towards the production of 4-aminobutyric acid. The mechanisms whereby feeding enhances SA, NO, and polyamine-mediated HR-linked defence whilst these are compromised with , which also increases the availability of nutrients to pathogens, are discussed.

Infrared gas phase spectroscopy is becoming very common in many life science applications. Here we present three types of trace gas detection systems based on CO₂ laser and continuous wave (cw) optical parametric oscillator (OPO) in combination with photoacoustic spectroscopy and cw quantum cascade laser (QCL) in combination with wavelength modulation spectroscopy. Examples are included to illustrate the suitability of CO₂ laser system to monitor in real time ethylene emission from various dynamic processes in plants and microorganisms as well as from car exhausts. The versatility of an OPO-based detector is demonstrated by simultaneous detection of ¹³C-methane and ¹²C-methane (at 3240 nm) at similar detection limits of 0.1 parts per billion by volume. Recent progress on a QCL-based spectrometer using a continuous wave QCL (output power 25 mW, tuning range of 1891–1908 cm^-1) is presented and a comparison is made to a standard chemiluminescence instrument for analysis of NO in exhaled breath.