Which type of sensors to analyze polluting gas from vehicle emissions

Question

I am thinking to develop a remote-sensing applications for vehicle pollutions. In such cases generally expensive optical IR and UV devices are used because more precise. These devices are generally ready-to-use and have also a graphical interfaces and other commands plus all the algorithms already implemented while I am interested only in the sensor part of such devices.

On the contrary electrochemical gas sensors are cheaper but much less precise. Generally these sensors have a response time from 20 to 60 seconds.

Suppose I can use a less precise estimate: can environmental polluting gas (electrochemical) sensors detect emissions of a low speed passing vehicle in a semi-closed environment such as a garage to have an approximate estimation?

My biggest fear is that these sensors are too slow to detect anything, even for a low-speed vehicle in load conditions.

Alternatively do you now any optical IR/UV open-path emitter/receiver sensor to analyze polluting gases from vehicle emissions and whose (electrical) output can be analyzed by embedded devices such as microcontrollers or micro-computers?

EDIT: The pollution gases due to road vehicles are typically CO, NO, NO2 but also CO2 should be monitored. These are the gases maybe with more concern but also SO2 might be important. The goal is to have an estimate on how much each vehicle is polluting: this estimate is not precise but it becomes important having large enough data to see for example which brand is most polluting. This is an example of device but it is used for industrial applications.

EDIT2 Let me reply to Bart's answer because it seems to me that the topic is not really clear here.

This has already being done (from late 80s-early 90s) using NDIR and UV. You do not measure the concentration directly but rather the ratio between a pollutant and CO2 because it is assumed to remain constant with the gases dispersion (so the wind effect should be minimized).

The idea is not to get a single precise costly and time-requiring measurement but to get many cheap less precise fast measurements. In this way it is possible to guess for example which brand or model is more polluting, and also to guess if a vehicle is polluting too much. With on-board expensive tests you confirm or reject those results.

From the analysis of emissions using extra data such as model/brand, category diesel or not you can provide also other estimations.

Answer 1

It's very inaccurate to measure for emissions of a vehicle passing by, in a non hermetically closed environment. The slightest breeze will make the measurements incoherent. Depending on the sensor and type of emission, you may not even detect it. Ideally, you measure in the exhaust of the vehicle, which can be considered a closed environment. For emission tests, they accumulate exhaust gases in 'bags' and then measure them, either accurately diluted with air or not. Constant volume flow systems are also used. Google for them to get an idea.

Regarding emissions, most electrochemical sensors are inferior to NDIR sensors, and most of them get consumed by measuring. They have limited shelf and usage life, and measurements can be spoiled by cross interfering gases. For instance, a CO sensor may see CO2 as CO, and thus reports a higher CO concentration than in reality. This also happens with NDIR sensors though. Using them directly in the exhaust gives them a too concentrated sample, and they'll get contaminated with sooth very quickly. So find a way to dilute the exhaust gas.

Sulphur based emissions are barely present, and thus hard to detect. NOx is also rather hard to detect, HC and CO are easily detected, CO2 is really easily detected because of it's abundance in exhaust gas.(roughly 15%) I'd recommend you to look into the typical emission concentrations in exhaust gas. It may give you a better idea about what and how to measure.

If you want to compare various fuels or vehicles, make sure they're operating in the exact same way, so the fuel or vehicle is the only thing that makes the difference. Otherwise the tests are meaningless.