Conversion of Units of Air Pollutant Concentrations.

The air pollutants are represented in either volume fraction/total volume or weight/volume. The former one may be of several types. For example, moles of pollutant/ total moles of air (mole fraction) in specific volume, number of molecules of pollutant/total number of molecules in the specific volume, etc. Overall, the concentration has quantity but no units. For example, 400 ppmv of CO2 is representation by 400 moles of CO2 / 1000000 moles of air in given volume. Therefore, it just a number. Another way of expressing the gas concentration is weight of pollutant/volume (g/m3 or mg/m3 or μg/m3).

The conversion of ppmv, ppbv to mg/m3 or μg/m3 respectively will depend on the molecular weight of the pollutant, and atmospheric temperature and pressure as follows.

(PPM/1000000)*(1000mg/1g)*(MW g/1 mole)*(1 mole/22.4L)*(1000L/1m3) at STP

Cancelling out the numerators and denominators will yield the following equation.

=> PPM*MW/22.4 mg/m3 at STP. This equation clearly shows that molecular weight is very important guess the converted value. However, the atmospheric properties changes dramatically. Therefore, by using the equation of state, we can calculate the volume occupied by 1 mole of gas as follows.

PV= nRT, where P is atmospheric pressure in hPa, V in Liters, n is number of moles, T temperature in Kelvin and the R is gas constant of 83.144 L hPa/K mole.

V= RT/P because n is 1 mole. Substituting this at 22.4 L in the above equation will give full controlled equation of MW, P, T that can be used to convert the pollutants into weights/volume.

Concentration in mg/m3 = ppm*WM*P/83.144*T

In the same way,

(PPB/1,000,000,000)*(1000,000 μg/1g)*(MW g/1 mole)*(1 mole/22.4L)*(1000L/1m3) at STP

Cancelling out the numerators and denominators will yield the following equation.

Therefore, the concentration in μg/m3 = ppb*MW*P/83.144*T


What is the concentration of CO2 in mg/m3 when it has 400 ppmv and the atmospheric temperature and pressure are 298K and 1010 hPa, respectively?

Concentration of CO2 = 400*44*1010/83.144*298 mg/m3

= 717.44 mg/m3

Problem 2:

What is the concentration of Ozone in μg/m3 when it has 80 ppbv, and the atmospheric temperature and pressure are 298K and 1010 hPa, respectively? Molecular weight of O3 is 48.

Concentration of O3 = 80*48*1010/83.144*298 μg/m3

= 156.5 μg/m3


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Do You Really Think That Urban/Peri-urban Green Infrastructure Planning Combats Ozone Pollution?

What is green Infrastructure? It is nothing but the green vegetation. It includes crops, forests, green rooftops, plants, etc. Do they really help reducing the ozone pollution? Not really ! Whether the green infrastructure is boon or curse depends on several factors. The previous blog “Gradual Increase of Complexity in the Ground-level Ozone Pollution Modeling Studies” showed some of the interactions between meteorology and chemistry in the formation of the ground-level ozone. As you walk through my YouTube channel named Tropopedia where you will learn the tropospheric chemistry, you will begin to understand that the chemistry is very non-linear. Depending on the state of the chemistry and the meteorology of specific location, the ozone may either form or destroy. As the blog “Gradual Increase of Complexity in the Ground-level Ozone Pollution Modeling Studies” explained, the vegetation, aka green infrastructure, modifies both meteorology due to the effect of roughness on the transport and the moisture fluxes, which critically influence on the state of the surface layer atmosphere. Because of being both inherent nature of fluxing VOCs and their dramatic effect by the state of the surface layer atmosphere such as humidity and temperature, the green infrastructure non-linearly affects the ozone-chemistry-without-the-vegetation. Therefore, there is no guarantee that the urban/peri-urban green infrastructure is going to combat ozone pollution of the city.

In a nutshell, there should be a rigorous city specific research on the pollution emissions, meteorology, and the chemistry of the region. A meticulous modeling studies are to be planned for the urban and peri-urban green infrastructure for understanding the effects of these changes on biogenic emissions and meteorology those significantly affect the ozone chemistry.

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Gradual Increase of Complexity in the Ground-level Ozone Pollution Modeling Studies.

Ground-level ozone is a serous pollutant especially in the summer season in the tropical and extra-tropical regions. It is to be noted that the ozone is not primary pollutant, meaning that the ozone is not directly emitted from the activities at the surface. However, it is a secondary pollutant formed in the atmosphere by primary pollutants such as nitrogen oxides (NOx) and volatile organic compounds (VOCs) under the sunlight, the chemical reaction speeds are augmented by atmospheric temperature. Therefore, we can now understand that the ozone levels are controlled by the emissions of NOx, VOCs, cloud-cover, air temperature, season, and the time of day.  In this, the season and the specific time of the day are invariant, but the NOx, VOCs, cloud-cover and air temperature are variables. While studying the ozone modeling studies, these should be critically taken care of.

Let’s now dissect these variables in terms of meteorology and chemistry. The former two are purely chemicals and the latter two are meteorological variables. What many air pollution modelers miss is the interaction between the meteorology and chemistry. Let’s see what it is. Although there are specifics of the each of the variables, all are commonly controlled by transport phenomenon, which is complex and in tern is controlled by several things. For example, complex surface structure such as mountainous terrain, roughness of the surface by forests, urban building, etc., etc. significantly impact on the transport of heat, moisture, momentum and chemical tracers. Although the heat and moisture fluxes are controlled by the land surface characteristics, for example, plants and water bodies, the transport of them significantly influence on both air temperature and cloud-clover.

The NOx and VOCs are emitted by both human-activities and natural sources. Vehicular emissions, industrial emissions, biogenic emissions are the sources of NOx and VOCs, despite having other sources such as lightening, agri-pesticide sprays, etc. The main mechanism of the ozone formations is that the HO radicals in the troposphere reacts with VOCs (CO) to form peroxy (hydro-peroxy) radicals. These peroxy radicals reacts with NO to form and NO2 and this NO2 dissociates in the presence of sunlight to form nascent oxygen, which can easily combine with atmospheric oxygen molecule (O2) to form ozone. It looks simple but the chemistry is very complex and complexity increases with the meteorology as explained. In addition to this, the complexity is further increased by the sea-sprays at the Ocean surfaces as the these contain reactive halogenated compounds that tightly interact with the ozone itself and destroys. The whole chemistry is taught at my YouTube channel at . Stay tuned at the channel for the periodic lecture videos.

In a nutshell, while modeling the ozone, one has to keep in mind that the emission levels of the precursors, season, surface terrain, surface characteristics such as vegetation and roughness, water bodies and the most importantly the chemical mechanisms. Please stay tuned and subscribe my YouTube channel at to walk you through all of these essentials.

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Is impact factor of a journal really important?

Research shows that, on an average, the impact of any journal is impacted by only 15% of articles and the rest of 85% enjoys the impact without any contribution. Furthermore, many of highly cited articles usually have more than one author and interestingly it is unknown about the percentage of contribution of each of the authors.

Impact factor is increased by the increase in the number of citation. It is to be noted that the research is neither for getting more citations nor for getting famous; it is for contributing the science. Let me explain with an example. A numerical model builder gets a lot of citation as it is used by a number of researchers, but it is to be noted that the model builder is a just compiler of numerous research done by a number of researchers. However, the builder gets more citations but the real researcher gets very less citations. Is the number of citations really matter???



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