Data-Driven Models for Estimating Dust Loading Levels of ERV HEPA Filters

With increasing global concerns regarding indoor air quality (IAQ) and air pollution, concerns about regularly replacing ventilation devices, particularly high-efficiency particulate air (HEPA) filters, have increased. However, users cannot easily determine when to replace filters. This paper proposes models to estimate the dust loading levels of HEPA filters for an energy-recovery ventilation system that performs air purification. The models utilize filter pressure drops, the revolutions per minute (RPM) of supply fans, and rated airflow modes as variables for regression equations. The obtained results demonstrated that the filter dust loading level could be estimated once the filter pressure drops and RPM, and voltage for the rated airflow were input in the models, with a root mean square error of 5.1–12.9%. Despite current methods using fewer experimental datasets than the proposed models, our findings indicate that these models could be efficiently used in the development of filter replacement alarms to help users decide when to replace their filters.

Relative Importance of High-Latitude Local and Long-Range Transported Dust to Arctic Ice Nucleating Particles and Impacts on Arctic Mixed-Phase Clouds

Dust particles, serving as ice nucleating particles (INPs), may impact the Arctic surface energy budget and regional climate by modulating the mixed-phase cloud properties and lifetime. In addition to long-range transport from low latitude deserts, dust particles in the Arctic can originate from local sources. However, the importance of high latitude dust (HLD) as a source of Arctic INPs (compared to low latitude dust (LLD)) and its effects on Arctic mixed-phase clouds are overlooked. In this study, we evaluate the contribution to Arctic dust loading and INP population from HLD and six LLD source regions by implementing a source-tagging technique for dust aerosols in version 1 of the US Department of Energy’s Energy Exascale Earth System Model (E3SMv1). Our results show that HLD is responsible for 30.7 % of the total dust burden in the Arctic, whereas LLD from Asia and North Africa contribute 44.2 % and 24.2 %, respectively. Due to its limited vertical transport as a result of stable boundary layers, HLD contributes more in the lower troposphere, especially in boreal summer and autumn when the HLD emissions are stronger. LLD from North Africa and East Asia dominates the dust loading in the upper troposphere with peak contributions in boreal spring and winter. The modeled INP concentrations show a better agreement with both ground and aircraft INP measurements in the Arctic when including HLD INPs. The HLD INPs are found to induce a net cooling effect (−0.24 W m−2 above 60° N) on the Arctic surface downwelling radiative flux by changing the cloud phase of the Arctic mixed-phase clouds. The magnitude of this cooling is larger than those induced by North African and East Asian dust (0.08 and −0.06 W m−2, respectively), mainly due to different seasonalities of HLD and LLD. Uncertainties of this study are discussed, which highlights the importance of further constraining the HLD emissions.

Asymmetric impacts on Mars' polar vortices from the 2018 Global Dust Storm

<p><strong>Introduction:</strong>  Like Earth, Mars possesses dynamical atmospheric features known as polar vortices. These are regions of cold, isolated polar air surrounded by powerful westerly wind jets which can create barriers to transport of atmospheric dust, water, and chemical species. They have a complex and asymmetrical (north/south) relationship with atmospheric dust loading [1]. Regional and global dust events have been shown to cause rapid vortex displacement [2,3] in the northern vortex, while the southern vortex appears more robust.</p> <p>Unlike Earth, Mars also experiences planet-encircling Global Dust Storms: spectacular, planet-spanning events which dramatically increase atmospheric dust loading. The most recent such event in 2018 (beginning at northern autumn equinox) [4] was observed by multiple spacecraft, including the ExoMars Trace Gas Orbiter (TGO) and the Mars Reconnaissance Orbiter (MRO), enabling the opportunity to study its effects on the polar vortices in detail.</p> <p>We do this by assimilating [5] spacecraft data from TGO’s Atmospheric Chemistry Suite (ACS) [6,7] and MRO’s Mars Climate Sounder (MCS) [8,9] into the LMD-UK Mars Global Climate Model [10], a 4D numerical model of the martian atmosphere.</p> <p><strong>Results: </strong>We present our recently published results [11], where we find that the 2018 GDS had asymmetrical impacts in each hemisphere: the northern polar vortex remained relatively robust, while the southern polar vortex was significantly disrupted. This asymmetry was due to both the storm’s latitudinal extent, which was greater in the south than in the north, and its timing, occurring as the southern vortex was already decaying after equinox. Both polar vortices and especially the northern showed reductions in their ellipticity, and this correlated with a reduction in high-latitude stationary wave activity in both hemispheres. We show that the characteristic elliptical shape of Mars’ polar vortices is the pattern of the stationary waves; this was suppressed during the storm by the shifting of the polar jet away from regions of high mechanical forcing in the north, and by the reduced polar jet due to the decreased meridional temperature gradient in the south. These asymmetric effects suggest enhanced transport into the southern, but not northern, polar region during GDS around northern autumn equinox, as well as more longitudinally symmetric transport around both poles.</p> <p><strong> </strong></p> <p><strong>References:</strong> [1] Waugh, D. W. et al (2016) <em>J. Geophys. Res. Planets, 121, </em>1770-1785. [2] Guzewich, S. D. et al (2016) <em>Icarus, 278, </em>100-118. [3] Mitchell, D. M. et al (2015) <em>Q.J.R. Meteorol. Soc., 141, </em>550-562. [4] Kass, D. M et al (2019) <em>GRL, 47</em>(23). [5] Lewis, S. R. et al (2007) <em>Icarus, 192</em>(2). [6] Korablev, O. et al (2018) <em>Space Sci. Rev., 214</em>(7). [7] Fedorova, A. A. et al (2020) <em>Science, 367</em>(6475). [8] McCleese, D. J. et al (2007) <em>JGR (Planets), 112</em>(E5). [9] Kleinböhl, A. et al (2009) <em>JGR (Planets), 114</em>(E10). [10] Forget, F. et al (1999) <em>JGR (Planets), 104</em>(E10). [11] Streeter, P. M. et al (2021) <em>JGR (Planets), </em>e2020JE006774.</p>

Influence of Dust on the Initiation of Neoproterozoic Snowball Earth Events

It has been demonstrated previously that atmospheric dust loading during the Precambrian could have been an order of magnitude higher than in the present day and could have cooled the global climate by more than 10 °C. Here, using the fully coupled atmosphere-ocean general circulation model CESM1.2.2, we determine whether such dust loading could have facilitated the formation of Neoproterozoic snowball Earth events. Our results indicate global dust emission decreases as atmospheric CO2 concentration (pCO2) decreases due to increasing snow coverage, but atmospheric dust loading does not change or even increases due to decreasing precipitation and strengthening June-July-August (JJA) Hadley circulation. The latter lifts more dust particles to high altitude and thus increases the lifetime of these particles. As the climate becomes colder and the surface albedo higher, the cooling effect of dust becomes weaker; when the global mean surface temperature is approximately -13 °C, dust has negligible cooling effect. The threshold pCO2 at which Earth enters a snowball state is between 280 to 140 ppmv when there is no dust, and is similar when there is relatively light dust loading (~4.4 times present-day value). However, the threshold pCO2 decreases dramatically to between 70 to 35 ppmv when there is heavy dust loading (~33 times present-day value), due to the decrease in planetary albedo which increases the energy input into the climate system. Therefore, dust makes it more difficult for Earth to enter a snowball state.