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Particulate pollution. The first thing that pops into mind is traffic. But are we sure that’s always the main responsible? In this first, and hopefully last, season of COVID-19 crisis, the time has come to turn our attention to intensive livestock and to the practice of zootechnical slurry spraying.

More and more scientific evidence are confirming particulate pollution is an aggravating factor for COVID-19 contagion and death count. SIMA’s analysis first supported a correlation between the high level of pollution in the Po Valley and the extremely high COVID-19 death rate. Siena University paper backed up the same conclusions concluding that the high level of pollution in Northern Italy should be considered a contributory cause of the high level of mortality. Lastly Harvard’s study correlated increase in mortality with the cumulative exposure to fine particle pollution (PM2.5 [1]).

Particulate pollution has various possible origins: direct sources (primary particulate) such as road transport and biomass burning, or secondary sources, that is derived from precursor gases that transform into particulate following physical-chemical transformations (secondary particulate). Secondary particulate may, in turn, be inorganic (Secondary Inorganic Aerosols – SIA) or organic (Secondary Organic Aerosols – SOA).

Although road traffic is commonly perceived as the main sources of particulate matter pollution, its importance varies according to areas and season of the year. In the Po Valley – during winter – the primary source of particulate matter is secondary particulate [2] which contributes for 54% to PM10. 36% of its mass comes from inorganic sources while 18% from organic ones. For PM2.5 the inorganic component contributes 49% and the organic for 26%.

So if almost half of PM2.5 comes from inorganic secondary particulate, what are its precursor gases? Sulfur dioxide (SO2), nitrogen oxides (NOx), ammonia (NH3) and volatile organic compounds (VOC).

In these times when industrial sources and traffic are considerably reduced by the lockdown, ammonia has become a critically important source of particulate pollution in the Po Valley.

According to Ispra data, 76.7% of ammonia in Italy is of zootechnical origin. However, this figure gets significantly worse in regions with a high zootechnical vocation. Like Lombardy, with 51% of Italian pig population and 24% of bovines, is undoubtedly the Region with the highest number of farm animals and with a staggering 98% of ammonia derived from livestock.

In the Po Valley, traffic is only the second most important source, adding to 17% of the mass of PM10 and 16% of the mass of PM2.5, while biomass burning is the third, contributing to 10% PM10 mass and 12% of PM2.5.

Yet, during the COVID-19 health emergency, Lombardy regional administration allowed for livestock slurry spreading, which generated peaks in particulate emissions that may have contributed to spreading the virus[3] and also further undermined public health?

Since traffic has almost stopped due to the lockdown, here comes my point: shouldn’t livestock slurry spreading be stopped as well, together with a consistent reduction in biomass burning, to protect public health?

It’s now time that politics start taking environmental factors more seriously and take action to limit ALL of the main sources of particulate emissions, in the immediate and for the future.

Taking also into account intensive livestock emissions.

[1] The abbreviations PM10 and PM2.5 indicate respectively the particulate matter having an average aerodynamic diameter of less than 10 µm and 2.5 µm.

[2] Larsen BR, Gilardoni S, Stenström K, et al (2012) Sources for PM air pollution in the Po Plain, Italy: II. Probabilistic uncertainty characterization and sensitivity analysis of secondary and primary sources. Atmos Environ 50:203–213. https://doi.org/10.1016/J.ATMOSENV.2011.12.038

[3] According to SIMA’s analysis and many other literature sources, particulate could act as a carrier for viruses.

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