Over the past decade, a range of sensor technologies became available on the market, enabling a revolutionary shift in air pollution monitoring and assessment. With their cost of up to three orders of magnitude lower than standard/reference instruments, many avenues for applications have opened up. In particular, broader participation in air quality discussion and utilisation of information on air pollution by communities has become possible. However, many questions have been also asked about the actual benefits of these technologies. To address this issue, we conducted a comprehensive literature search including both the scientific and grey literature. We focused upon two questions: (1) Are these technologies fit for the various purposes envisaged? and (2) How far have these technologies and their applications progressed to provide answers and solutions? Regarding the former, we concluded that there is no clear answer to the question, due to a lack of: sensor/monitor manufacturers' quantitative specifications of performance, consensus regarding recommended end-use and associated minimal performance targets of these technologies, and the ability of the prospective users to formulate the requirements for their applications, or conditions of the intended use. Numerous studies have assessed and reported sensor/monitor performance under a range of specific conditions, and in many cases the performance was concluded to be satisfactory. The specific use cases for sensors/monitors included outdoor in a stationary mode, outdoor in a mobile mode, indoor environments and personal monitoring. Under certain conditions of application, project goals, and monitoring environments, some sensors/monitors were fit for a specific purpose. Based on analysis of 17 large projects, which reached applied outcome stage, and typically conducted by consortia of organizations, we observed that a sizable fraction of them (~ 30%) were commercial and/or crowd-funded. This fact by itself signals a paradigm change in air quality monitoring, which previously had been primarily implemented by government organizations. An additional paradigm-shift indicator is the growing use of machine learning or other advanced data processing approaches to improve sensor/monitor agreement with reference monitors. There is still some way to go in enhancing application of the technologies for source apportionment, which is of particular necessity and urgency in developing countries. Also, there has been somewhat less progress in wide-scale monitoring of personal exposures. However, it can be argued that with a significant future expansion of monitoring networks, including indoor environments, there may be less need for wearable or portable sensors/monitors to assess personal exposure. Traditional personal monitoring would still be valuable where spatial variability of pollutants of interest is at a finer resolution than the monitoring network can resolve.

Applications of low-cost sensing technologies for air quality monitoring and exposure assessment: How far have they gone?

Part One: One-Dimensional Dynamics Examples of Dynamical Systems Preliminaries from Calculus Elementary Definitions Hyperbolicity An example: the quadratic family An Example: the Quadratic Family Symbolic Dynamics Topological Conjugacy Chaos Structural Stability Sarlovskiis Theorem The Schwarzian Derivative Bifurcation Theory Another View of Period Three Maps of the Circle Morse-Smale Diffeomorphisms Homoclinic Points and Bifurcations The Period-Doubling Route to Chaos The Kneeding Theory Geneaology of Periodic Units Part Two: Higher Dimensional Dynamics Preliminaries from Linear Algebra and Advanced Calculus The Dynamics of Linear Maps: Two and Three Dimensions The Horseshoe Map Hyperbolic Toral Automorphisms Hyperbolicm Toral Automorphisms Attractors The Stable and Unstable Manifold Theorem Global Results and Hyperbolic Sets The Hopf Bifurcation The Hnon Map Part Three: Complex Analytic Dynamics Preliminaries from Complex Analysis Quadratic Maps Revisited Normal Families and Exceptional Points Periodic Points The Julia Set The Geometry of Julia Sets Neutral Periodic Points The Mandelbrot Set An Example: the Exponential Function

An introduction to chaotic dynamical systems (2nd edition), by Robert L. Devaney. Pp 336. £34·95. 1989. ISBN 0-201-13046-7 (Addison-Wesley)

From low-cost sensors to high-quality data: A summary of challenges and best practices for effectively calibrating low-cost particulate matter mass sensors

Calibration of low-cost PurpleAir outdoor monitors using an improved method of calculating PM2.5

Carcinogenic organic content of particulate matter at urban locations with different pollution sources.

. In this paper we evaluate characteristics of three optical particulate matter sensors/sizers (OPS): high-end spectrometer
11-D (Grimm, Germany), low-cost sensor OPC-N2 (Alphasense, United Kingdom) and in-house developed MAQS
(Mobile Air Quality System), which is based on another
low-cost sensor – PMS5003 (Plantower, China), under realistic conditions of strong and mild urban pollution. Results were compared against a reference
gravimetric system, based on a Gemini (Dadolab, Italy), 2.3 m 3  h −1 air sampler, with two channels (simultaneously measuring PM 2.5 and PM 10 concentrations).
The measurements were performed in Sarajevo, the capital of Bosnia-Herzegovina, from December 2019 until May 2020.
This interval is divided into period 1 – strong pollution – and period 2 – mild pollution. The city of Sarajevo is one of the most polluted cities in Europe in terms of particulate matter: the average concentration of PM 2.5 
during the period 1 was 83  µ g m −3 , with
daily average values exceeding 500  µ g m −3 . During period 2, the average concentration of
PM 2.5 was 20  µ g m −3 . These conditions represent a good opportunity to test optical devices against the reference instrument in a wide range of ambient particulate matter (PM) concentrations. The effect of an in-house developed diffusion dryer for 11-D is discussed as well. In order to analyse the mass distribution of particles, a scanning mobility particle sizer (SMPS), which together with the 11-D spectrometer gives the full spectrum from nanoparticles of diameter 10 nm to coarse particles of diameter 35  µ m, was used.
All tested devices showed excellent correlation with the
reference instrument in period 1, with R2 values between 0.90 and 0.99 for daily average PM concentrations. However, in period 2, where the range of concentrations was much narrower,
 R2 values decreased significantly, to values from 0.28 to 0.92. We have also included results of a 13.5-month long-term comparison of our MAQS sensor with a nearby beta attenuation monitor (BAM) 1020 (Met One Instruments, USA) operated by the United States Environmental Protection Agency (US EPA), which showed similar correlation and no observable change in performance over time.

/pdf/evaluation-of-optical-particulate-matter-sensors-under-43a3yi8ndf.pdf

Evaluation of optical particulate matter sensors under realistic conditions of strong and mild urban pollution

Vertical temperature profiles represent a very important factor for various analytical and numerical studies, such as weather forecasts, air pollution models and CFD simulations These temperature profiles are especially important during the winter periods, when temperature inversions occur The cities in the natural valleys, such as the city of Sarajevo, B&H, are strongly affected by this phenomenon In this paper, a method for quantitative characterization of vertical temperature profiles, which is based on the in-house developed data acquisition system and the unmanned aerial vehicle, is presented Comprehensive calibration and verification procedure was performed and explained in details Field measurements were focused on the winter period and extreme temperature inversion scenarios The correlation with the air pollution in the city, for the same period, was discussed as well

/pdf/experimental-study-of-temperature-inversions-above-urban-5g41rkntwo.pdf

Experimental study of temperature inversions above urban area using unmanned aerial vehicle

/pdf/mobile-measurements-of-particulate-matter-concentrations-in-1i67t2xzcz.pdf

Mobile Measurements of Particulate Matter Concentrations in Urban Area

/pdf/temperature-inversion-measurements-in-sarajevo-valley-using-2dr6f9nhwq.pdf

Temperature Inversion Measurements in Sarajevo Valley Using Unmanned Aerial Vehicles

/pdf/new-approach-of-measuring-toxic-gases-concentrations-2qbybcc887.pdf

Adnan Masic

Papers

Evaluation of optical particulate matter sensors under realistic conditions of strong and mild urban pollution

Experimental study of temperature inversions above urban area using unmanned aerial vehicle

Mobile Measurements of Particulate Matter Concentrations in Urban Area

Temperature Inversion Measurements in Sarajevo Valley Using Unmanned Aerial Vehicles

New Approach of Measuring Toxic Gases Concentrations: Principle of Operation