International Research Journal of Engineering and Technology (IRJET) e-ISSN: 2395-0056
Volume: 12 Issue: 04 | April 2025 www.irjet.net p-ISSN: 2395-0072
A Literature Survey on Optical Particle Counter (OPC) Technologies
Mahesh Nikam1 , Prachi A Deshpande2
1 M.E.II, Dept. of Electronics & Tele-Communication Engineering, Dhole Patil College of Engineering, Kharadi, Pune, Maharashtra, India
2 Professor, Dept. of Electronics & Tele-Communication Engineering, Dhole Patil College of Engineering, Kharadi, Pune, Maharashtra, India.
Abstract - Theadverseeffectsofparticulatematter(PM)on human health and the environment have led to increased attention on air quality monitoring over the past few decades.[1]Inresponsetothisneed,mobile,low-cost,andrealtime PM detection devices have become more prominent in research and application. Recently, researchers have introduced innovativemobile opticalparticlecounters(OPCs) to meet the growing demand for real-time PM monitoring in both indoor and outdoor environments. However, there remains a scarcity of comprehensive reviews on these new mobile and compact PM measurement technologies. This paper aims to address this gap by reviewing the latest advancementsinmobileOPCsforparticulatematterdetection, with a focus on applications ranging from general air quality monitoring to specific uses like vehicle exhaust analysis.
Key Words: mobile optical particle counters, particulate matter,airqualitymonitoring,observationvolume,vehicle exhaust.
1.INTRODUCTION
OpticalParticleCounters(OPCs)operateontheprincipleof laser scattering, a technique that allows these devices to detect and estimate the size of airborne particles by measuringhowtheyscatterlight.InanOPC,alightsource, typically a laser or an LED, emits a focused beam into a chamber through which air is drawn. As particles pass through this light beam, they scatter light in various directions.Detectorspositionedaroundthechambercapture thescatteredlight,andtheintensityofthisscattered light correlates with the particle's size: larger particles scatter morelight,whilesmallerparticlesscatterless.[2]
The underlying scattering phenomenon relies on Mie scatteringtheorywhenparticlesizesarecomparabletothe wavelength of the light. Mie theory, a subset of Maxwell’s electromagnetictheory,describeshowparticleswithinthe wavelengthrangescatterlight,allowingforfairlyaccurate particle sizing. The OPC’s detectors capture specific scatteringpatterns,whicharethenanalysedbythedevice’s processingunittoclassifyparticlesintosizebins.Theresult is a size distribution of particles in the sampled air, often representedasPM1,PM2.5,orPM10toindicateparticlesof specificdiametersinmicrometres.
In short, when the outside air passes through the light collectionchambertheparticlesinsampledairarescattered by the light beam. The photoelectric conversion unit convertsthescatteredlightsignalintoavoltagepulsesignal, whichispre-amplifiedandconvertedintodigitalsignalafter ADconversion.Themeasurednumberofvoltagepulsesis thenumberofparticles,andtheamplitudeofvoltagepulses reflectsthesizeoftheparticle’sopticallyequivalentparticle size.
Recentadvancementsinsignalprocessinganddataanalysis havefurtherenhancedtheaccuracyandresolutionofOPCs. These improvements allow OPCs not only to measure particlesizeandconcentrationbutalsotoprovidereal-time data,makingthemvaluabletoolsforairqualitymonitoring.
1.1 Importance of Air Quality Monitoring
Airqualitymonitoringisessentialbecauseparticulatematter (PM) poses a significant threat to human health and the environment. Fine particulate matter, particularly PM 2.5 (particles with a diameter of 2.5 um or less) and PM 10 (particleswithadiameterof10umorless),canhavesevere health impacts. Studies have linked PM exposure to respiratoryandcardiovasculardiseases,aggravatedasthma, decreased lung function, and even premature mortality. Additionally, PM plays a major role in environmental degradation, impacting visibility, damaging crops, and contributingtoclimatechange.
Monitoringairquality,specificallyparticulatelevels,iscrucial for understanding exposure risks, informing public health decisions, and developing pollution control strategies. However,traditionalairqualitymonitoringmethods,suchas gravimetric analysis, require stationary infrastructure and
Fig -2:Basiccomponentsofthelight-scatteringoptical particlecounter.[2]
International Research Journal of Engineering and Technology (IRJET) e-ISSN: 2395-0056
Volume: 12 Issue: 04 | April 2025 www.irjet.net p-ISSN: 2395-0072
involveatime-consumingprocessofsamplecollectionand laboratoryanalysis.Theselimitationshavecreatedademand for more accessible, real-time, and mobile monitoring solutions.
1.2 Current Demand for Mobile, Cost-Effective,and Real-Time PM Monitoring
To address these limitations, there has been a rising demandformobile,low-cost,andreal-timePMmonitoring devicesthatcanbedeployedflexiblyacrossvarioussettings. PortableOPCsfulfilthisneedbyprovidingreal-timedataon particlesizeandconcentrationinacompactform.Theyare now being widely used in both indoor and outdoor environments, allowing individuals, researchers, and organizations to monitor PM levels conveniently. [3] [4] These devices are particularly beneficial in environments that require agile monitoring solutions, such as areas impactedbytrafficemissions,constructionsites,andeven personalexposuretrackinginoccupationalsettings.
1.3 Focus of the Review
Despite the advances in mobile OPC technology, there remainsascarcityofcomprehensivereviewscoveringthe latestdevelopmentsinthisfield.Thispaperaimstoaddress thisgapbyreviewingrecentadvancementsinmobileoptical particlecountersforPMdetection.[5]Thefocuswillbeon technological innovations, current applications, and emergingtrendsinOPCtechnology,withparticularattention to improvements in portability, sensitivity, and data connectivity. By consolidating recent findings, this review seeks to provide a valuable resource for researchers and professionalsinterestedinmobileairqualitymonitoringand thefutureofopticalparticlecountersinthefield.
2. Background of Optical Particle Counters (OPCs)
2.1 Different PM Monitoring Technologies
Particulate Matter (PM) monitoring has evolved through various technologies, each with unique operating principles,advantages,andlimitations.Themostestablished methodistheGravimetricandFilter-BasedTechnique,which involvescollectingairborneparticlesonafilteroveraspecific duration. These filters are then weighed under controlled laboratory conditions to determine the particle mass concentration.Thismethodishighlyaccurateandformsthe basisofregulatoryPMmonitoring.However,itisinherently time-consuming,requiresstationaryinfrastructure,andlacks real-time feedback, which limits its utility in dynamic or mobilemonitoringscenarios.
Another established method is the Beta Attenuation Monitor(BAM)andElectrostatictechniques.BAMworksby measuring the attenuation of beta particles as they pass through particle-laden filters, offering high precision and regulatory-gradedata.Electrostatic monitors,ontheother hand,usechargedplatestoattractairborneparticles.Both
methodsofferhighsensitivityandreliabilitybutaregenerally bulkyand expensive,making themunsuitable for portable applications.
Optical Particle Counters (OPCs) use light-scattering principles to detect and size particles in real-time. As particlespassthroughalightbeam,theintensityofscattered light captured by photodetectors correlates with the particlesize.OPCsprovidethedualadvantageofreal-time measurementandparticlesizedistribution,thoughtheycan be influenced by ambient humidity or particle refractive index,whichmayaffectaccuracy.
Tomakeparticlesensingmoreaffordable,Low-CostOPCs have been developed. These systems mimic the lightscattering principle of standard OPCs but use lower-cost components.Whilenotasaccurate,theyareidealforcitizen science,communitymonitoring,andwidespreaddeployment, thoughtheirlimitationsinaccuracyandprecisionmustbe considered.
MobilePhone-BasedOPCsrepresentanemergingclassof ultra-portablesensors.Theyutilizethesmartphone’scamera andLEDflashtodetectscatteredlightfromparticlesandthen apply imageanalysisalgorithms to estimateconcentration levels.Thesesystemsareconvenientandhighlyaccessible, but theirsensitivityandprecisionare typicallylower than dedicatedinstruments.[6][7]
Recent research has introduced more sophisticated systemsliketheComplicatedParabolicCollector(CPC)-Based OPC, which captures scattered light over wide angles to enhance detection of submicron particles without using filters.Thissetupishighlysensitivebutmayrequireprecise opticalalignment,affectingusability.[8][9]
OtherspecializedinstrumentsincludeSilicon-BasedOPCs, whichintegratelaserdiodesandphotodiodesintocompact, microfabricatedsiliconchambers.Thesedevicesarepowerefficientandsuitableforwearabletechnology,althoughtheir fabrication is complex and usually targeted at specific applications.[10][11][12]
Furthermore, Fresnel Ring Lens-Based OPCs utilize concentric lens structures to focus scattered light onto detectorswithhighangularprecision,improvingparticlesize classification.[13] [14] Similarly, Drilled Lens-Based OPCs enhancelightcollectionefficiencyandareoptimizedforsmall particlesensitivity,albeitwithcertaintrade-offsinangular collectionandbeamisolation.[15]
2.2 Key components of OPC
AcommercialOPC,regardlessofwhetherit'slow-costor high-end,followsamodulardesignarchitecturebuiltaround the core principle of light scattering. It begins with a light source,typicallyalaserorahigh-intensityLED.Thissource emitsa narrow, collimatedbeam oflight directed acrossa flow channel. The wavelength of the light is chosen to optimizethescatteringinteractionwithparticlesofinterest, typicallyrangingfrom400–700nm
International Research Journal of Engineering and Technology (IRJET) e-ISSN: 2395-0056
Volume: 12 Issue: 04 | April 2025 www.irjet.net p-ISSN: 2395-0072
Theparticledetectionchamberisdesignedtocontrolthe airflowanddirectparticlesthroughthebeampathuniformly. This chamber must ensure laminar flow to prevent turbulence, which could lead to counting errors or signal noise.
When a particle crosses the beam, it scatters light at variousangles.Thisscatteredlightiscapturedbytheoptical collectionsystem,whichcanincludemirrorsorlensesthat direct the light toward a photodetector. Depending on the particlesizeandlightwavelength,eitherMiescattering(for particles~0.1to10µm)orRayleighscattering(forsmaller particles)dominatesthesignalbehavior.
The photodetector (usually a photodiode or avalanche photodiode) converts the optical energy into an electrical signal.Thestrengthofthissignalcorrelateswiththeparticle size.Thisanalogsignalisthenamplifiedanddigitizedinthe signalprocessingunit,whichassignseachdetectedeventtoa particlesizebinandcountsitaccordingly.
To ensure accuracy, particularly in bright or dusty environments, a stray light suppression system such as optical traps or baffles is used to block or absorb nonscattered light. This improves the signal-to-noise ratio, ensuringtheintegrityofthemeasureddata.
2.3 TechnologicalAdvancements in OpticalParticle Counters (OPCs)
TheevolutionofOpticalParticleCounters(OPCs)spans over a century, beginning with foundational theoretical developmentsandadvancingintotoday'scompact,real-time, andintelligentsensingsystems.
In the early beginnings (1900–1950s), the theoretical basisforOPCswasestablishedthroughthedevelopmentof light scattering theory. Pioneers like Lord Rayleigh and Gustav Mie formulated the mathematical frameworks for Rayleigh and Mie scattering, respectively. These theories describehowparticlesscatterlightdependingontheirsize relativetothewavelength,layingthegroundworkforlater particle detection techniques. During this period, early experimental light scattering detectors were developed, although they were rudimentary and used primarily in academicorlaboratorysettings.Thesedevicesdemonstrated the feasibility of using light for particle detection, but practicalimplementationremainedlimited.
Thepost-warera(1950s–1970s)witnessedasignificant leapwiththeinventionofthelaser,whichofferedacoherent, focused, and stable light source ideal for precise optical measurements. This innovation drastically improved the sensitivity and resolution of particle detection systems. Consequently,thefirstcommercialOPCsemergedduringthis phase, primarilytargetingapplications inclean roomsand industrial quality control where precise monitoring of particulatecontaminationwasessential.
Anewwaveofinnovationfollowedinthe1980sthrough the2000s,characterizedbyadvancesinminiaturizationand
integration.Theadventofsemiconductortechnologiesand Micro-Electro-Mechanical Systems (MEMS) enabled the development of smaller, portable OPCs with significantly lower power consumption. In parallel, the introduction of LED-basedlightsourcesreducedsystemcostsandextended product lifespan, making OPCs more accessible. The refinement of optical lenses and photo detector designs, coupled with the integration of digital signal processing, further improved the resolution and accuracy of particle measurements. These improvements made it possible to reliablydetectfinerparticulatematter,suchasPM2.5,inreal time.
The2000sto2010susheredinthedigitalandlow-cost eraofOPCtechnology.Duringthistime,LED-basedlow-cost OPCsgainedtraction,facilitatingwide-scaledeploymentfor consumer air quality monitors and community-driven environmentalsensingnetworks.Paralleltocostreduction, wireless and IoT integration became common features, enabling OPCs to stream data in real time via mobile and cloud-based platforms. This connectivity allowed for decentralized monitoring and enhanced responsiveness in bothurbanandruralcontexts.
Finally, in the 2020s and beyond, OPCs have undergone remarkable advancements in sensitivity and accuracy. Modern systems now employ advanced optical materials, refined sensor calibration techniques, and AI-powered processing algorithms, bringing the performance of some low-costOPCsclosertothatofreference-gradeinstruments. Anotherkeydevelopmenthasbeentheintroductionofmultichannel OPCs, which can simultaneously analyze particles across multiple size ranges, thereby providing a more detailedandaccuraterepresentationofparticulatepollution. In addition, the integrationof OPCs into droneand mobile platforms has enabled flexible and high-resolution monitoring of air quality in diverse environments from urbanstreetsandindustrialzonestoremoteorhazardous locationssuchaswildfireregionsandvolcanicsites.
2.4 Applications of OpticalParticle Counters (OPCs)
Optical Particle Counters (OPCs) have emerged as indispensabletoolsacrossawiderangeofdomainsdueto theirabilitytodetectandquantifyparticulatematterinrealtime. Their versatility has led to applications in environmentalscience,public health,industry,agriculture, aerospace,andtransportation.
In the field of environmental monitoring, OPCs are primarilyusedforairqualityassessmentsinbothindoorand outdoor environments. These sensors can measure concentrationsofparticulatemattersuchasPM1,PM2.5,and PM10,offeringinsightintopollutantlevelsfromsourceslike vehicleemissions,industrialdischarge,andnaturaldust.For ambientairqualitymonitoring,OPCsprovidereal-timedata crucialforregulatorycompliance.Environmentalprotection agencies and municipalities deploy these sensors to track pollutionpatterns,enforceemissionstandards,andinform thepublicaboutpotentialhealthrisks.
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Under the umbrella of health and personal exposure monitoring,OPCsareusedintwokeyareas.First,personal airqualitymonitorsequippedwithOPCsallowindividuals, especially those with asthma, allergies, or respiratory vulnerabilities toassesstheairtheybreathethroughoutthe day.Thesecompact,wearabledeviceshavebecomepopular among health-conscious users and researchers studying personal exposure trends. Second, in occupational health settings,suchasmanufacturingplantsorconstructionsites, OPCs help ensure that workers are not overexposed to harmfulparticulatemattersuchasdust,weldingfumes,or fibers.Thesemeasuressupportworkplacesafetyregulations andminimizelong-termrespiratoryrisks.
In industrial applications, OPCs are integrated into systemsfordustmonitoringinmanufacturingenvironments. Industriessuchascementproduction,mining,andmetallurgy rely on these sensors to maintain dust levels within permissible limits. OPCs also form a key component of ContinuousEmissionsMonitoringSystems(CEMS)usedin factories and power plants. These systems monitor particulate emissions at the stack in real-time, allowing operatorstodetectanomaliesandensurecompliancewith airqualityregulations.
TheagriculturalsectoralsobenefitsfromOPCtechnology. In agricultural air quality monitoring, these sensors track airborneparticlesgeneratedduringactivitieslikeplowing, harvesting, and fertilizer or pesticide application. By monitoringtheparticulatepollutionfromfarmingoperations, stakeholders can mitigate their impact on nearby communities.Additionally,OPCsarebeingexploredforpest and disease monitoring, where they detect microscopic particles related to fungal spores or pest activity, offering earlywarningsofcropinfestationsorplantdiseases.
Intherealmofaerospaceanddrone-basedenvironmental sensing, OPCs are mounted on unmanned aerial vehicles (UAVs) to perform aerial monitoring of air quality. This applicationisespeciallyuseful inareasthataredifficultto access or potentially hazardous, such as volcanic regions, wildfire zones, or chemical spill sites. Furthermore, researchers use drones with OPCs in weather and environmental research, examining aerosol distribution at various altitudes to understand their influence on cloud formation,radiationbalance,andclimatedynamics.
Lastly,intheautomotiveandtransportationsector,OPCsare employed in vehicle emissions testing. These devices measure particulate emissions, particularly from diesel engines, to evaluate compliance with environmental regulations. Their real-time capabilities also support innovations in green transportation and pollution control technologies.
2.5 Current All types of OPCs in market
The figure-2 presents a comprehensive comparison of various particulate matter (PM) sensors from different manufacturers, highlighting key parameters such as light source,detectionmethod,particlesizerange,concentration
measurementcapability,andweight.Mostsensors,suchas theSPS-30bySensirion,PMS-7003byPlanttower,andSDS011 by NOVA, use a 660nm light source and photodiode detectors,coveringacommonparticlesizerangeof0.3to10
Fig -2:DifferenttypesofOPC’s
µm and concentration range up to 1000 µg/m³. Notably, advancedsensorsliketheMOPCfromBrechtelandthePOPS fromHandixCorporationemployhigh-poweredlasersources with PMT (photomultiplier tube) boards, achieving high sensitivityforparticlesassmallas0.13µmandmeasuringin particlenumberconcentration(#/cm³)insteadofmass.On the heavier end of the spectrum, instruments such as the MINIWRAS1371fromDuragGroupweighover8kgandcan detect ultrafine particles down to 0.010 µm, making them suitableforhigh-precisionindustrialorresearchapplications. Conversely, compact and lightweight models like the PM1006K(20gm)andSPS-30(27gm)areidealforportable or consumer-grade air quality monitoring. This range of sensors demonstrates the trade-off between sensitivity, measurementcapability,andportability,cateringtodifferent applicationsfromindoorairqualitymonitoringtoadvanced scientificresearch.
Recent advancements in particulate matter (PM) sensing technologieshaveledtothedevelopmentofawiderangeof low-cost and compact sensors for ambient air quality monitoring.Asshowninthesensorcomparison,devicessuch astheSPS-30(Sensirion)[19]andPMS-7003(Planttower) utilize 660 nm light sources with photodiode detection to measure particles within the 0.3 to 10 µm range. These sensorsareincreasinglyusedinbothconsumerandresearch applications due to their affordability and portability. However,challengessuchashumidityinterferencecanaffect dataaccuracy;researcherslikeAndreaDiAntonioetal.[16] have proposed relative humidity correction methods to improvereliabilityinvaryingenvironmentalconditions.On the other hand, high-precision instruments like the MOPC (Brechtel) and POPS (Handix), which use photomultiplier tube(PMT)boardsandoperateatshorterwavelengths,offer greatersensitivitydownto0.13µm,makingthemsuitablefor scientificanalysis.AsPopeandDockery[17]emphasize,fine particulate matter (especially PM2.5) poses serious health risks, linking exposure to cardiovascular and respiratory diseases. Consequently, the growing use of IoT-based monitoring systems [21] and open-source air quality initiativessuchasAirBeam2[20]reflectsashifttowardmore
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decentralizedandcommunity-drivenenvironmentalhealth monitoring.ManufacturerslikeAlphasense[18]continueto contributetothisevolutionbyprovidingsensorcomponents thatbalanceperformanceandaccessibility.
3. CONCLUSIONS
Inconclusion,thesurgeindemandforportable,real-time airqualitymonitoringsystemshascatalysedadvancements in mobile optical particle counters (OPCs). These devices now enable precise, in-situ measurements of particulate matter (PM1, PM2.5, PM10) by size, mass, and number concentration, making them invaluable tools in industry, regulatorymonitoring,andconsumermarkets.Thisreview has highlighted key technological innovations in OPCs, covering enhanced sensing components, integration techniques,andsensorminiaturization.
ThetrajectoryofOPCdevelopmentsuggestsa nearfuture wheresensorswillbecomeincreasinglysensitive,compact, and capable of autonomous, real-time detection across diverse environmental conditions. Emerging trends point toward breakthroughs in miniaturization and advanced detection algorithms, leveraging new materials, photonic integration, and machine learning for more refined data processing. These innovations, driven by the need for accessible and precise air quality data, signal a transformativeshifttowardsOPCsthatarenotonlyportable but also highly scalable for widespread use in urban, industrial,andevenpersonalhealthapplications.
ACKNOWLEDGEMENT
The authors may thank Dr. Abhijeet Dandavate Principal DPCOE,Kharadi,Pune
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