key: cord-0865714-zktj4lwg
authors: Bhaganagar, Kiran; Bhimireddy, Sudheer
title: Local Atmospheric Factors that enhance Air-borne Dispersion of Coronavirus - High-fidelity Numerical Simulation of COVID19 case study in Real-Time
date: 2020-09-17
journal: Environ Res
DOI: 10.1016/j.envres.2020.110170
sha: 480986a65a2475ada3272304477a27273af5e198
doc_id: 865714
cord_uid: zktj4lwg

The spatial patterns of the spreading of the COVID19 indicate the possibility of airborne transmission of the coronavirus. As the cough-jet of an infected person is ejected as a plume of infected viral aerosols into the atmosphere, the conditions in the local atmospheric boundary layer together dictate the fate of the infected plume. For the first time - a high-fidelity numerical simulation study - using Weather-Research-Forecast model coupled with the Lagrangian Hybrid Single-Particle Lagrangian Integrated Trajectory model (WRF-HYSPLIT) model has been conducted to track the infected aerosol plume in real-time during March 9-April 6, 2020, in New York City, the epicenter of the coronavirus in the USA for comparing the morning, afternoon and evening release. Atmospheric stability regimes that result in low wind speeds, low level turbulence and cool moist ground conditions favor the transmission of the disease through turbulence energy-containing large-scale horizontal “rolls” and vertical thermal “updrafts” and “downdrafts”. Further, the wind direction is an important factor that dictates the direction of the transport. From the initial time of release, the virus can spread up to 30 minutes in the air, covering a 200-m radius at a time, moving 1 – 2 km from the original source.

geographical regions, the pandemic appears to be spreading at varying rates. COVID-19 clearly 25 spreads more easily than other respiratory diseases (e.g., SARS Severe Acute Respiratory 26 Syndrome). Micro-scaled virus particles that drift in the air or land on surfaces have multiplied 27 into a global pandemic. Air motions transport the micro-particles, with the extent of horizontal 28 and vertical transport of the virus cloud depending on the wind conditions at that moment in time 29

and at that location. The virus can reach the ground and potentially spread to someone passing 30 through that region during the lifespan of the virus. On the other hand, if transported vertically 31 away from the ground, it disperses and loses its affinity to affect healthy individuals. 32

Recent studies used statistical analysis to explore the correlation between the local 34 meteorological factors and the COVID-19 pandemic in various regions of the world. Transport 35 of pollutant particles in the atmosphere due to turbulence dispersion is significantly higher than 36 molecular dispersion resulting from fluid viscosity; in addition, the local meteorology dictates 37 the trajectory and extent of a pollutant's mixing in the atmosphere (Stull,1993; Moeng & 38 Sullivan, 1994) . The studies considered air temperature, humidity, pollution levels, seasonal 39 The posed research question will provide insights into a possible pathway for community 129 transmission of the disease. Existing research clearly indicates the local air conditions, such as 130 air circulation patterns, air temperature, and humidity, dictate the aerosol/blob of particles 131 transported in the atmosphere. Turbulence is the most efficient mixing agent; the infected blob 132 released into surrounding turbulent air currents is transported by turbulence, entraining ambient 133 air, and becoming diluted. Atmospheric turbulence could transport the infection much faster and 134 farther than would be possible in indoor conditions. As such, the present study seeks to use a 135 high-resolution numerical model to obtain accurate air patterns in the New York region during 136 the peak time period of COVID-19 in order to understand the transport processes influencing dispersion, Lagrangian particles were released from 2 m elevation at the grid center. The particle 163 emissions rate was set to 1E7 per hour and released for 0.01 hours (~ 36 sec). The particle 164 concentration output from HYSPLIT was measured in mass units per unit volume (mass m -3 ) and 165 was collected every minute for a duration of 30 minutes from the time of release. Released 166 particles are defined to be spherical in shape, with a diameter of 0.125 µm and a density of 1.7 g 167 cm -3 . The half-life of released particles is set to 5 days. Table 1 The regimes of the PBL is classified depending on the wind speeds and the relative 203 measure of L with respect to the PBL depth z (ζ= z/L), such as class A with strong convection 204 and weak winds to class F with stable stratification and weak winds (Golder, 1972) . 205

Fifteen different instances of release conditions during the period of March 9 th -April 6 th under 207 realistic meteorological conditions are analyzed (Table 1) . We first investigate the transport 208 scales of the cloud under different PBL regimes, and then analyze the role of the meteorological 209 variables on the dynamics of transport and mixing. In Table 1 the fifteen different instances in 210 the analysis, are arranged from highly convective ζ to weakly stable stratified PBL regimes. The 211 columns correspond to ζ, release date and time, T, z, L, wind-speed at 10 m height, wind shear 212 close to the ground (dU/dz), temperature gradient close to the ground (dT/dz), TKE, and moisture 213 content on the ground (amount of moisture per kg. of air). 214

The analysis for the release of the blob on April 2 0700 CDT is presented here. This 215 corresponds to a PBL regime of ζ = -3.5 (Table 1) . Appendix Figure 2 a-f shows the trajectory 216 of the blob for times at t = 2 min, 5 min, 10 min, 15 min, 20 min and 29 min after release (i.e., t= 217 0 min). The color maps correspond to the average concentration from 0-10 meters above the 218 ground overlaid on a geographical map of the region. The plan view shows the horizontal east-219 west and north-south directions. The (0,0) location is the blob's point of release corresponding to 220 latitude and longitude of (74W, 40N), as shown by the red circle. Released as a point source at t 221 = 0, the blob starts to move away from the point of release and also expands horizontally as it 222 spreads. At 10 minutes following the release time, the direction of the blob is towards the north-223 west of the initial location, and at 15 min and beyond, it continues to move in that direction while 224 growing in size. After 10 minutes, the blob is 2.5 km east and 1 km north of the original location, 225 and it moves towards New Jersey at 15 minutes. At 29 minutes, it is 7 km east and 6 km north of 226 its original location. As the blob moves, the ambient air mixes with the contaminant, diluting the 227 blob. In this case, it takes around 30 minutes to be completely diluted. The trajectory of the blob and the mixing can be explored using a micro-climate analysis 235 at 0700 hours CDT on April 2 nd . WRF simulations reveal that the PBL is in a moderately 236 convective regime characterized by a deep PBL layer of 1022 m, winds at a moderate speed of 237 5.2 m/s, and moderate turbulence blowing over the region. There is a cool ground temperature of 238 278.6K with a moisture content of 3.5e-3 kg/kg of air, and the wind-shear is stronger than the 239 thermal gradient on the ground ( Table 1) To understand the differences in trajectory for different release conditions, two additional sets of 247 cases are presented with the release conditions of April 5 0700 hours CDT (ζ=-5.28) and March 248 10, 1900 hours CDT (ζ=2.75). WRF simulations demonstrate that the PBL exhibits different 249 characteristics for these regimes. For example, the PBL is in a moderately convective regime; 250 however, it is shallow in depth with low winds and weak turbulence generated from a 251 combination of low shear-driven and low buoyancy-driven production when ζ=-5.28. Turbulence 252 is generated due to a small negative temperature gradient (sink of TKE production) and a 253 positive high wind-shear (source of TKE production). Appendix Fig. 4 a-f shows the trajectory 254 of the blob at 5 min, 10 min, 15 min, 20 min, 25 min, and 30 min after the release time. At 5 255 minutes, the blob expands in area; however, the transport of the blob is slow compared to the ζ=-256 3.5 case. The blob continues to move eastwards for a distance of 0.5 km and 2.5 km from the 257 source, 10 minutes and 20 minutes after release, respectively. The region is influenced by 258 stronger southwest marine winds and weaker circulation over the land of less than 5m/s, 259 resulting in an elliptical region of coverage. Appendix Fig. 5 a- In summary, the response of the blob to atmospheric turbulence is dictated by PBL 268 characteristics, such as wind shear, temperature gradient, energy containing horizontal rolls, and 269 turbulence.

In weakly/moderately convective regimes, the PBL contains buoyancy-and Next, we analyze the area covered by the blob as it moves in time. All fifteen cases are 282 analyzed here. Fig. 1a shows the area covered by the virus-blob in time as it expands due to the 283 local turbulence until it dilutes due to mixing with the atmosphere. Fig. 1b shows the mixing 284 ratio of the blob (ratio of contaminant density at a given time to the initial density in the blob). 285

The spreading rate at which it mixes with the ambience before dilution strongly depends on the In the two cases corresponding to stable PBL regimes, ζ = 0.63, 0.75, the 296 PBL depth is deep and the TKE production is mainly due to the wind-shear as the contribution 297 from buoyancy-generated TKE is very low. This suggests that these regimes represent transition 298 from a neutral to a stable regime. The conditions are characterized by low winds of around 5 m/s 299 and moderate shear-driven turbulence. The mixing is dictated by purely shear-driven processes. 300

The blob expands to a maximum area of 1. Table 1 ).

J o u r n a l P r e -p r o o f Next, we discuss the variations in the atmospheric stability and local climate of the New York 309 region. The urban boundary layer in New York City is influenced greatly by the sea breeze due 310 to the ocean's proximity. We analyze the role of local meteorological variables on the direction 311 of transport from the initial release location and the meteorological variables that influence the 312 direction. Fig. 2 a- The study provides robust evidence to the recent report by the National Academy of 406

Science raising concerns about transmission of SARS-COV-2 via aerosols generated from 407 droplets [13] . The report indicated an airflow modeling study following the SARS-CoV 

Investigation of effective 423 climatology parameters on COVID-19 outbreak in Iran

Assessment of the plume dispersion due to chemical attack on 426

Syria. Natural Hazards

Short-term passive tracer plume dispersion in convective 428 boundary layer using a high-resolution WRF-ARW model

Performance Assessment of Dynamic Downscaling of WRF 430 to Simulate Convective Conditions during Sagebrush Phase 1 Tracer Experiments

Highly effective in Inactivating and Inhibiting SARS-CoV-2 Replication

First data analysis about possible COVID-19 virus airborne diffusion due to air 435 particulate matter (PM): The case of Lombardy (Italy)

Violent respiratory events: on coughing 437 and sneezing

Longitudinal instabilities and secondary flows in the planetary boundary layer: A 439 review

Causal empirical estimates suggest COVID-19 transmission rates are highly 441 seasonal medRxiv

Factors determining the diffusion of COVID-19 and suggested strategy to prevent future 443 accelerated viral infectivity similar to COVID

Two mechanisms for accelerated diffusion of COVID-19 outbreaks in regions with 446 high intensity of population and polluting industrialization: the air pollution-to-human and human-to

Centers for Disease Control and Prevention. Coronavirus disease 2019 (COVID-19): Symptoms of 452 coronavirus 2020

Coronavirus disease (COVID-2019) situation reports. 2020. (Accessed 8th of

The role of environmental factors to transmission of SARS-CoV-2 457 (COVID-19)

Climate affects global patterns of COVID-19 early outbreak dynamics

Relations among stability parameters in the surface layer

Temperature, humidity, and wind speed are associated 463 with lower Covid-19 incidence

Transmission of COVID-19 virus by 465 droplets and aerosols: A critical review on the unresolved dichotomy

Quantity and size 467 distribution of cough-generated aerosol particles produced by influenza patients during and after illness

A comparison of shear-and buoyancy-driven planetary boundary-layer 472 flows

Rapid Expert consultation on the 474 possibility of Bio Aerosol Spread of SARS-CoV-2 for the COVID-19 Pandemic

Anomalous atmospheric circulation favored the spread of COVID-19 in Europe, medRxiv

Association of COVID-19 global distribution and 482 environmental and demographic factors: An updated three-month study

Review of non-local mixing in turbulent atmospheres: Transilient turbulence theory

Aerosol and Surface Stability of SARS-486

CoV-2 as Compared with SARS-CoV-1

Evidence of airborne transmission of the severe acute respiratory syndrome virus

A real-time,high-fidelity simulation of blob of virus filled cough-jet released in the atmosphere has been conducted

Appendix Fig. 6b , the (v-w) rolls on April 3 rd are narrower but deeper, with a width of 1.5 km 331 and extending to 1.8 km deep. 332

A computationally intensive study has been performed to accurately represent the 334 dispersion processes and the factors influencing the transport and mixing of the cloud or blob of 335 virus-filled micro-particles released due to coughing, sneezing, or similar events into the 336 atmosphere. The motivation of the study is two-fold. First, the New York region has become the 337 epicenter of coronavirus spread in the USA, with a steady increase in disease spread beginning in 338March and continuing to date. Therefore, there is an urgent need to conduct a study specific to 339 the New York region during this period in order to gain an understanding of the key factors that 340 correlate with the spread of the disease. Second, there is no knowledge regarding the possibility 341 of infection spread due to coughing/sneezing and air-current conditions in the atmosphere. As 342 such, this study provides an important direction for future research, with direct implications on 343 social distancing protocols and face masks for protection. 344Fifteen different instances of conditions corresponding to morning, afternoon and