Landfalling atmospheric rivers (ARs) frequently trigger heavy and sometimes prolonged precipitation, especially in regions with favored orographic enhancement. The presence and strength of ARs are often described using the integrated water vapor (IWV) and the integrated vapor transport (IVT). However, the associated precipitation is not directly correlated with these two variables. Instead, the intensity of precipitation is mainly determined by the net convergence of moisture flux and the initial degree of saturation of the air column. In this study, a simple algorithm is proposed for estimating the heavy precipitation attributable to the IVT convergence. Bearing a strong resemblance to the Kuo‐Anthes parameterization scheme for cumulus convection, the proposed algorithm calculates the large‐scale primary condensation rate (PCR) as a proportion of the IVT convergence, with a reduction to account for the general moistening in the atmosphere. The amount of reduction is determined by the column relative humidity (CRH), which is defined as the ratio of IWV to its saturation counterpart. Our analysis indicates that the diagnosable PCR compares well to the forecast precipitation rate given by a numerical weather prediction model. It is also shown that the PCR in an air column with CRH < 0.50 is negligibly small. The usefulness of CRH and PCR as two complements to standard AR analysis is illustrated in three case studies. The potential application of PCR to storm classification is also explored.

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Abstract. Biomass burning emissions emit a significant amount of trace gases and aerosols and can affect atmospheric chemistry and radiative forcing for hundreds or thousands of kilometres downwind. They can also contribute to exceedances of air quality standards and have negative impacts on human health. We present a case study of an intense wildfire plume from Siberia that affected the air quality across the Pacific Northwest on 6–10 July 2012. Using satellite measurements (MODIS True Colour RGB imagery and MODIS AOD), we track the wildfire smoke plume from its origin in Siberia to the Pacific Northwest where subsidence ahead of a subtropical Pacific High made the plume settle over the region. The normalized enhancement ratios of O3 and PM1 relative to CO of 0.26 and 0.08 are consistent with a plume aged 6–10 days. The aerosol mass in the plume was mainly submicron in diameter (PM1 ∕ PM2.5 = 0.96) and the part of the plume sampled at the Whistler High Elevation Monitoring Site (2182 m a.s.l.) was 88 % organic material. Stable atmospheric conditions along the coast limited the initial entrainment of the plume and caused local anthropogenic emissions to build up. A synthesis of air quality from the regional surface monitoring networks describes changes in ambient O3 and PM2.5 during the event and contrasts them to baseline air quality estimates from the AURAMS chemical transport model without wildfire emissions. Overall, the smoke plume contributed significantly to the exceedances in O3 and PM2.5 air quality standards and objectives that occurred at several communities in the region during the event. Peak enhancements in 8 h O3 of 34–44 ppbv and 24 h PM2.5 of 10–32 µg m−3 were attributed to the effects of the smoke plume across the Interior of British Columbia and at the Whistler Peak High Elevation Site. Lesser enhancements of 10–12 ppbv for 8 h O3 and of 4–9 µg m−3 for 24 h PM2.5 occurred across coastal British Columbia and Washington State. The findings suggest that the large air quality impacts seen during this event were a combination of the efficient transport of the plume across the Pacific, favourable entrainment conditions across the BC interior, and the large scale of the Siberian wildfire emissions. A warming climate increases the risk of increased wildfire activity and events of this scale reoccurring under appropriate meteorological conditions.

&lt;p&gt;&lt;strong&gt;Abstract.&lt;/strong&gt; Biomass burning emissions emit a significant amount of trace gases and aerosols and can affect atmospheric chemistry and radiative forcing for hundreds or thousands of kilometers downwind. They can also contribute to exceedances of air quality standards and have negative impacts on human health. We present a case study of an intense wildfire plume from Siberia that affected the air quality across the Pacific Northwest on July 6&amp;#8211;10, 2012. Using satellite measurements (MODIS True Colour RGB imagery and MODIS AOD), trajectories, and dispersion modelling, we track the wildfire smoke plume from its origin in Siberia to the Pacific Northwest where subsidence ahead of a subtropical Pacific High made the plume settle over the region. The normalized enhancement ratio of O&lt;sub&gt;3&lt;/sub&gt; and PM&lt;sub&gt;1&lt;/sub&gt; relative to CO of 0.26 and 0.09 are consistent with a plume aged 6&amp;#8211;10&amp;#8201;days. The aerosol mass in the plume was mainly submicron in diameter (PM&lt;sub&gt;1&lt;/sub&gt;/PM&lt;sub&gt;2.5&lt;/sub&gt; = 0.97) and the part of the plume sampled at the peak of Whistler Mountain was 87&amp;#8201;% organic material. Stable atmospheric conditions along the coast limited the initial entrainment of the plume and caused local anthropogenic emissions to buildup. A synthesis of air quality from the regional surface monitoring networks describes changes in ambient O&lt;sub&gt;3&lt;/sub&gt; and PM&lt;sub&gt;2.5&lt;/sub&gt; during the event and contrasts them to baseline air quality estimates from the AURAMS chemical transport model without wildfire emissions. Overall, the smoke plume contributed significantly to the exceedances in O&lt;sub&gt;3&lt;/sub&gt; and PMM&lt;sub&gt;2.5&lt;/sub&gt; air quality standards and objectives that occurred at several communities in the region during the event. Peak enhancements in 8-hr O&lt;sub&gt;3&lt;/sub&gt; of 34&amp;#8211;44&amp;#8201;ppbv and 24-hr PM&lt;sub&gt;2.5&lt;/sub&gt; of 14&amp;#8211;32&amp;#8201;&amp;#956;g/m&lt;sup&gt;3&lt;/sup&gt; were attributed to the effects of the smoke plume across the Interior of British Columbia and at the Whistler Peak high elevation site (2182&amp;#8201;m ASL). Lesser enhancements of 10&amp;#8211;12&amp;#8201;ppbv for 8-hr O&lt;sub&gt;3&lt;/sub&gt; and of 4&amp;#8211;9&amp;#8201;&amp;#956;g/m&lt;sup&gt;3&lt;/sup&gt; for 24-hr PM&lt;sub&gt;2.5&lt;/sub&gt; occurred at Whistler Peak and across coastal British Columbia and Washington State. The findings suggest that the large air quality impacts seen during this event were a combination of the efficient transport of the plume across the Pacific, favorable entrainment conditions across the BC interior and the large scale of the Siberian wildfire emissions. A warming climate increases the risk of increased wildfire activity and events of this scale re-occurring under appropriate meteorological conditions.&lt;/p&gt;

This study describes the development of a model using standard air quality monitoring data (PM2.5, NO2, relative humidity, and PM speciation profiles) to provide near real-time estimates of time-resolved extinction in regions where direct optical monitoring is not available. Applications of the model include extension of spatial coverage of a visibility network, testing various air quality scenarios to inform visibility management, and as a tool for setting visual air quality standards in impacted airsheds.