No abstract

HFO-1234yf (2,3,3,3-tetrafluoropropene) was proposed as an automobile air conditioner (MAC) refrigerant worldwide. However, its atmospheric degradation product is the highly soluble and phytotoxic trifluoroacetic acid (TFA), which persists in aquatic environments. We used a global three-dimensional chemical transport model to assess the potential environmental effects resulting from complete future conversion of the refrigerant in all MAC to HFO-1234yf in China, the United States, and Europe. The annual mean atmospheric concentrations of HFO-1234yf were 2.62, 2.20, and 2.73 pptv, and the mean deposition rates of TFA were 0.96, 0.45, and 0.52 kg km yr, in three regions. The regional TFA deposition sources mainly came from emissions within the same region. The annual TFA deposition in the North Pole region was lower than the global average and mainly originated from European emissions. A potential doubling in the future HFO-1234yf emissions in China mainly affected the local TFA depositions. The TFA concentrations in rainwater were strongly affected by the regional precipitation rates. North Africa and the Middle East, regions with scant rainfall, had extremely high TFA concentrations. The rainwater concentrations of TFA during individual rain events can exceed the level considered to be safe, indicating substantial potential regional risks from future HFO-1234yf use.

Abstract. Deep convection possesses markedly distinct properties at different spatiotemporal scales. We present an original high-resolution (4 km, hourly) unified data product of mesoscale convective systems (MCSs) and isolated deep convection (IDC) in the United States east of the Rocky Mountains and examine their climatological characteristics from 2004 to 2017. The data product is produced by applying an updated Flexible Object Tracker algorithm to hourly satellite brightness temperature, radar reflectivity, and precipitation datasets. Analysis of the data product shows that MCSs are much larger and longer-lasting than IDC, but IDC occurs about 100 times more frequently than MCSs, with a mean convective intensity comparable to that of MCSs. Hence both MCS and IDC are essential contributors to precipitation east of the Rocky Mountains, although their precipitation shows significantly different spatiotemporal characteristics. IDC precipitation concentrates in summer in the Southeast with a peak in the late afternoon, while MCS precipitation is significant in all seasons, especially for spring and summer in the Great Plains. The spatial distribution of MCS precipitation amounts varies by season, while diurnally, MCS precipitation generally peaks during nighttime except in the Southeast. Potential uncertainties and limitations of the data product are also discussed. The data product is useful for investigating the atmospheric environments and physical processes associated with different types of convective systems; quantifying the impacts of convection on hydrology, atmospheric chemistry, and severe weather events; and evaluating and improving the representation of convective processes in weather and climate models. The data product is available at https://doi.org/10.25584/1632005 (Li et al., 2020).

Large missing daytime HONO sources have been reported by many previous studies around the world. Possible HONO sources include ground heterogeneous conversion, aerosol heterogeneous formation, soil emission, and photochemical production. In this study, a consistent 1D framework based on regional and 3D chemical transport models (CTMs) was used to analyze the unknown daytime HONO sources in 14 cases worldwide. We assume that the source of HONO from aerosols is through NO 2 hydrolysis (not including its oxidation products) and that non-local mixing effect is negligible. Assuming all the missing unknown HONO source is from the ground, it would imply a NO 2 -to-HONO ground heterogeneous conversion exceeding 100% in daytime, which is unphysical. In contrast, a strong R 2 reaching up to 0.92 is found between the unknown HONO sources and the products of aerosol wet surface area and short-wave radiation. Because the largest unknown daytime HONO sources are found in China due to high concentrations of aerosols and NO 2 , we derive an optimized NO 2 uptake coefficient on the basis of these measurements. The 3D CTM simulations suggest that in some regions of central, eastern, and southwestern (e.g. SiChuan province) China, the aerosol HONO source has the greatest effects on ozone (>10 ppbv) and OH (>200%) in winter. In January, the simulated particulate sulfate level over these three regions increases by 6-10 μg m −3 after including the aerosol-HONO source, which helps reduce the previous model underestimation of sulfate production in winter. Additional measurement studies that target the daytime HONO sources will be essential to a better understanding of the mechanisms and resulting effects on atmospheric oxidants.