The annual Independence Day concert and fireworks show was held on the National Mall July 4, despite dense cloud cover that obscured the fireworks for some. (A Capitol Fourth/PBS) 
 
 If you were watching Washington’s Fourth of July fireworks outside on Monday night and also happened to catch PBS’s broadcast of “A Capitol Fourth,” you might have noticed something looked…a little off. 
 
 The actual weather in Washington was cloudy and misty, making it quite difficult to view the fireworks. But on “A Capitol Fourth,” the annual concert special that airs live from the West Lawn of the U.S. Capitol, many of the fireworks (primarily in the second half of the display) looked glorious in a clear sky. Immediately, people started commenting on Twitter: 
 
 [Tom Bergeron previews PBS’s ‘A Capitol Fourth’: No, he’s not worried about rain] 
 
 When the cloud coverage is bad and PBS plays fake footage of the fireworks in DC — Alexis Sadoti (@AlexisASadoti) July 5, 2016 
 
 https://twitter.com/tinpant/status/750139052448362496 
 
 Not cool @pbs…. Fake footage of fireworks on the Fourth???? It's cloudy and rainy in DC. Those shots are clearly not from tonight. — Chris Wallgren (@seawall77) July 5, 2016 
 
 Just flipped over to PBS here in the newsroom. Wow that is stock footage. They did have a few live shots, you could see the foggy conditions — JimMacKayOnAir (@JimMacKayOnAir) July 5, 2016 
 
 Another giveaway? On TV, you couldn’t see the construction scaffolding on the Capitol building, which has been there for many months. 
 
 Thanks for your fake coverage of the July 4th, Washington DC fireworks PBS! No clouds, No scaffolding on the Capitol #July4thPBS,#beAshamed — JoeyV (@therealjoeyjoe) July 5, 2016 
 
 As soon as the show ended, producers from Capital Concerts owned up to the fact that not all of its footage was from the live fireworks show. (In the first segment of the display, while singer Cassadee Pope was singing, some scenes did show a cloudy sky.) “We showed a combination of the best fireworks from this year and previous years. It was the patriotic thing to do,” the “Capitol Fourth” account tweeted. 
 
 We showed a combination of the best fireworks from this year and previous years. It was the patriotic thing to do. #July4thPBS — A Capitol Fourth (@July4thPBS) July 5, 2016 
 
 A “Capitol Fourth” spokeswoman confirmed to us that because the weather was so overcast, the producers pulled together a combination of clips “to make the best television show.” She added this is the first time the producers have had to take such measures. 
 
 Still, some viewers were not happy that PBS wasn’t upfront about the pre-recorded nature of the fireworks: 
 
 @July4thPBS should have at least let viewers know "some portions pre-recorded" — Melissa Jensen (@jensenmama) July 5, 2016 
 
 It was a fraudulent thing to do.@July4thPBS @nbcwashington — Ben Anderson (@AndStrats) July 5, 2016 
 
 @July4thPBS How is using stock video patriotic? If I wanted that, I'd watch YouTube. #fake #July4thPBS — Thomas Rainer (@ThomasRainerDC) July 5, 2016 
 
 Feeling personally victimized by @PBS and #capitalfourth for using stock firework footage. It's cloudy and gross today not perfectly clear — Katherine Sisemore (@KSisemore) July 5, 2016 
 
 …and so on. 
 
 1 of 14 Full Screen Autoplay Close Skip Ad × A soggy Fourth for fireworks on the Mall in Washington View Photos Rain or shine, the fireworks display is an annual tradition over the nation’s capital on Independence Day. Caption Rain or shine, the fireworks display is an annual tradition over the nation’s capital on Independence Day. July 4, 2016 Spectators on the Mall watch the fireworks show. Jabin Botsford/The Washington Post Buy Photo Wait 1 second to continue. 
 
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 Why ‘The Devil Wears Prada’ is one of those rare movies that’s better than the book ||||| PBS was pummeled on social media after it acknowledged having spliced in video of previous years' Washington, D.C., fireworks in its live "A Capitol Fourth" broadcast Monday night. 
 
 Hundreds of viewers complained on the annual show's Twitter and Facebook pages that the fireworks display couldn't be live because the images were in clear weather: 
 
 An image from PBS' 'A Capitol Fourth' Independence Day show Monday night. 
 
 Washington, however, was heavily overcast and foggy Monday night — which was readily apparent as the pyrotechnics faded into dense clouds: 
 
 Fireworks explode Monday night over the Lincoln Memorial on the National Mall in Washington, D.C. AP 
 
 About 10 p.m. ET, the show's Facebook and Twitter pages acknowledged that the supposedly "live" show was, in fact, " a combination of the best fireworks from this year and previous years." 
 
 We showed a combination of the best fireworks from this year and previous years. It was the patriotic thing to do. #July4thPBS — A Capitol Fourth (@July4thPBS) July 5, 2016 
 
 Reaction online was swift and savage: 
 
 @July4thPBS Only in DC could a PBS show become a scandal #July4thPBS #capitolfourth — thedcfloridian (@thedcfloridian) July 5, 2016 
 
 @July4thPBS How is using stock video patriotic? If I wanted that, I'd watch YouTube. #fake #July4thPBS — Thomas Rainer (@ThomasRainerDC) July 5, 2016 
 
 #Blessed to see the fireworks from my apt window & watch #July4thPBS. Tho, the fireworks out my window don't look like @pbs. #fake? ?????? — Tina (@tinpant) July 5, 2016 
 
 Not cool @pbs.... Fake footage of fireworks on the Fourth???? It's cloudy and rainy in DC. Those shots are clearly not from tonight. — Chris Wallgren (@seawall77) July 5, 2016 
 
 PBS representatives didn't immediately return NBC News' calls for comment Monday night. ||||| As clouds swirled over dress rehearsal for PBS’s “A Capitol Fourth” on Sunday morning on the West Lawn of the U.S. Capitol, host Tom Bergeron couldn’t help but throw in a few jokes about the weather as he practiced his lines via teleprompter. 
 
 “Thunder, lightning and torrential downpours!” Bergeron said on stage as he reeled off what audiences could expect during PBS’s annual Fourth of July fireworks and concert special. Later, he added, “We’ve only had six tornado warnings.” Although there were laughs all around, would Bergeron panic if he woke up Monday morning for the actual show and saw a gray sky? 
 
 [D.C.-area forecast: Rain likely for the Fourth, but not necessarily a total washout all day and evening] 
 
 Tom Bergeron, host of “A Capitol Fourth.” (Capital Concerts) 
 
 “Oh, no,” he told us backstage. He’s not worried about potential rain. “The first rule of improv, as I was taught it, is you say yes to everything. You don’t tense up. … I’m open for anything. That doesn’t bother me.” 
 
 Of course, it helps that Bergeron has seen basically everything in his decades as an Emmy-winning TV host, from “Hollywood Squares” to “America’s Funniest Home Videos.” He’s especially unfazed when it comes to live television, given that he has co-hosted ABC’s hit reality competition show “Dancing With the Stars” since 2005, and that’s always a frenzied couple of hours. 
 
 So even though “A Capitol Fourth” (airing on PBS at 8 p.m., live-streamed on PBS.org and Facebook Live) is on a tight schedule, packed with performances from Smokey Robinson, Kenny Loggins, Sutton Foster, Yolanda Williams, Cassadee Pope and Christopher Jackson, you can expect some of Bergeron’s signature ad-libs between proceedings. He’s especially jazzed to meet Jackson, who plays George Washington in the smash musical “Hamilton”; Bergeron saw the show last month and loved it, although he quipped during rehearsal that he had to take out a second mortgage to afford tickets. 
 
 And is Bergeron especially eager to have the best seat in the house for the fireworks, with his prime perch on the West Lawn? 
 
 “To be honest with you, the fireworks — even though that gets such attention — is the least interesting part of it to me. I love that first moment walking out on the stage, seeing all the people, seeing the Capitol building … and there’s all the incredible talent,” Bergeron said. “Fireworks, they’re nice, but I’ve seen a lot of fireworks. Sorry, that’s not what gets me here. Everything else gets me here.” ||||| When you look up at those Fourth of July fireworks, say hooray for the red and white — but give a special cheer for the blue. 
 
 "People have been trying to make a good blue for 500 years, and they haven't quite perfected it," John Conkling, a chemistry professor emeritus from Washington College in Maryland, told NBC News. "Purples we're getting good at. Pinks are decent. But blues are a big challenge." 
 
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 Conkling should know: He literally wrote the book on the chemistry of pyrotechnics, and is featured in a new video on the subject from the American Chemical Society. The way Conkling sees it, scientists still have a lot to learn about the science of fireworks, thousands of years after the Chinese invented them. 
 
 Even today, the Chinese are setting the pace in the global fireworks industry. "More and more of the product these days is made in China, so if there was a lot of research and development, it'd be going on in China," Conkling said. 
 
 But there's still something to be said for American know-how: Every year, specialty fireworks manufacturers in the United States come up with fresh twists — with a big assist from the U.S. Army. 
 
 "Pyrotechnics is one leg of a four-legged stool in the energetics field," said James Wejsa, chief of the pyrotechnics technology and prototyping division at the Army's Picatinny Arsenal in New Jersey. "We also have the propellants, the explosives and the warheads. The military is the one who really drives the technology in this area, and usually what you have are spin-offs in the commercial sector." 
 
 'Greener' fireworks from the Army 
 
 For example, Picatinny has been working on more environmentally friendly ingredients for the pyrotechnics that produce colored signals as a means of non-verbal communication on the battlefield. 
 
 "Getting new dyes and new ways to burn the formulations with different fuels is a challenge," Wejsa said. "The last thing you want is to have a soldier saying, 'Is that red smoke or violet smoke?' It could be the difference between 'shoot me' and 'don't shoot me,' you know what I'm saying?" 
 
 It turns out that the new formulations just might improve your neighborhood Fourth of July fireworks show as well. The Army has been working on a spin-off with Fireworks by Grucci, one of the biggest companies in the business. 
 
 "These formulations burn brighter and they burn clearer because there's less smoke," Wejsa said. "It's almost like going to high definition, because you don't have the smoke obscuring the color." 
 
 Wejsa and his team are making fireworks "greener" in more ways than one: They've developed a technique to produce a bright green flare using boron carbide rather than toxic barium compounds, a smoke grenade that emits less hazardous smoke, timing fuses and other pyrotechnics that don't leave potentially toxic perchlorate residues, and explosive primers that don't use lead. 
 
 "Our goal is to spin this off to commercial applications," Wejsa said. 
 
 The future of fireworks 
 
 So what's next? "The newest thing has been to try to perfect colors that normally people don't see in fireworks," Conkling said. Like a bright true blue, or really good orange. 
 
 "All the blues we see now have a copper compound that's at the heart of the reaction," Conkling explained. "The battle you're fighting here is that colored fireworks are brightest at high temperatures, but the copper emitter is not stable at high temperatures. So you have to play a game of 'The Price Is Right.'" 
 
 To produce an especially orange blast, chemists try blending run-of-the-mill sodium yellow-orange with red, but the job requires a lot of experimentation. The resulting recipes are closely held. "The old U.S. fireworks makers used to say there were some formulas they wouldn't even tell their grandmothers," Conkling said. 
 
 NBC News file 
 
 Another frontier for fireworks has to do with creating shapes in the sky. "It's common to see the heart pattern, the five-pointed star, multiple rings," Conkling said. "The logical extension of that would be letters, and being able to orient the letter up in the sky so you could spell out 'NBC' or something like that." 
 
 Fireworks by Grucci is already experimenting with a couple of technologies called PixelBurst and SkyEtching to create complicated patterns, letters and numbers. The technique was used for the countdown in Grucci's Dubai New Year's Eve display — and although the numbers are a bit hard to read, Conking is confident pyrotechnicians will work out the bugs. "It isn't like putting a man on the moon to do that," he said. 
 
 Will your fireworks be rained out? A guide for East Coasters 
 
 Besides the military, theme parks are the main drivers for innovation in fireworks displays — and sometimes it's not strictly about the fireworks. For example, the "Frozen" spectacular that's due to make its debut at Disney's Hollywood Studios in Florida this week will supplement the evening sky show with a video projection of social-media "selfies" submitted by parkgoers during the day. 
 
 When Conkling attends the Fourth of July festivities with his four grandchildren in Chestertown, Maryland, he'll be watching for the blues in the red-white-and-blue. But like most fans of the Fourth, he recognizes that a fireworks display isn't just a chemistry experiment. The winning formula also requires a healthy dose of flag-waving — and a flair for drama. 
 
 "One thing I like is a well-paced show," he told NBC News. "There should be no dead spots in it, and there should be some variety in it. It's not just the same thing over and over again." 
 
 IN-DEPTH 
 
 First published July 4 2014, 8:45 AM ||||| This story was reported by Travis Andersen and Martin Finucane of the Globe staff and Globe correspondents Zachary T. Sampson, Claire McNeill, Faiz Siddiqui, Jennifer Smith, Oliver Ortega, and Rachel Riley. It was written by Andersen. 
 
 Thousands of revelers packed the Charles River Esplanade Thursday night for the 41st annual Boston Pops Fireworks Spectacular, dancing to live music and cheering for a nighttime display in the skies that came off just before heavy rains and lightning forced an evacuation of the festivities. 
 
 Spectators came from around the country, many wearing patriotic shirts, hats, facepaint, and other eye-catching accessories. They were treated to a spectacular 20-minute fireworks display that began shortly after 10 p.m. and lit up the night sky. 
 
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 But the festivities ended early, and abruptly. 
 
 At about 10:30 p.m., a public address announcer informed the crowd that State Police had ordered an evacuation of the area. Heavy rain began falling soon after, interspersed with lightning flashes, forcing spectators to flee, some walking and some running. 
 
 David Procopio, a State Police spokesman, wrote in an e-mail that organizers “shot fireworks off early at 10:01 and cut them on short notice because of the severe weather.” 
 
 “We then ordered the evacuation and cleared the Oval and Lagoon areas out,” he said. “Evacuation was relatively orderly.” 
 
 The downpour forced the Pops to skip its live performance of Tchaikovsky’s “1812 Overture,” a cherished segment of the annual July 4 celebration, disappointing some revelers. 
 
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 “They took away the best part of the whole concert,” said Pam Capeless, 62, of Randolph. 
 
 City officials said the Boston Common Garage was available for people who needed to wait out the worst of the storm. 
 
 Saresh Alambath, 36, of Wilmington left the fireworks and huddled with family members on a porch on Revere Street to escape the soaking rains. 
 
 “Suddenly, it started pouring,” Alambath said. 
 
 Scott Ebner, 40, of the South End got caught in the rain at the edge of the Esplanade. 
 
 “Little cold, but the world won’t end,” he said. 
 
 Procopio, the State Police spokesman, said organizers moved up the fireworks “once we knew that a strong storm cell was moving toward eastern Mass.” 
 
 He added, “Once it was clear that a strong storm cell was going to impact Boston, we ordered the concert be shortened (no “1812 Overture,” among other cuts) and began evacuating the Esplanade.” 
 
 He said late Thursday night that authorities were not aware of any storm-related injuries. 
 
 The threat of severe weather had prompted officials to move the traditional July Fourth festivities up one day, marking the first time since 1992 that the extravaganza was rescheduled. Spectators began filling the Hatch Shell area at about 4:30 p.m., and the rain held off until just after the evacuation order was given. 
 
 Jubilant concertgoers danced throughout the evening to live performances from the Pops, the Beach Boys, and others. The fireworks display followed and got rave reviews. 
 
 “Very beautiful,” said Louis Yu, a Boston University medical student. 
 
 Revelers also enjoyed the music. 
 
 Steve Przecioski, 63, of Phoenix, danced with his wife and daughter as the Beach Boys played “Fun Fun Fun,” one of their many hits. 
 
 “They still have it,” said Przecioski. “They really do.” 
 
 When the festivities began in the late afternoon, organizers made sure that the crowd was festooned in patriotic garb. 
 
 Phil Touchette of B4 Productions, the company putting on the event, passed out miniature American flags and said staff members were distributing some 25,000 flags and foam Statue of Liberty crowns. 
 
 “We’re just trying to make it a patriotic event here,” he said. “That’s what it’s all about.” 
 
 Claire Richards, 86, of Randolph, sat in a wheelchair earlier in the evening on the outskirts of the concert area and wore patriotic beads around her neck. She said she was attending the celebration for the first time in many years. 
 
 “We might as well enjoy it, because you never know what tomorrow brings,” Richards said. “There’s nothing like being here in person. It’s a happy occasion, a beautiful day.” 
 
 Concertgoers spread tarps and blankets, set down beach chairs, and kicked off their shoes as they carved out territory for the event. 
 
 “We came out specifically for this,” said Bruce Masatsugu, 61, of San Francisco, who waited for hours Thursday with his family to get a spot near the stage. “And we figured we might as well go do it — do it right.” 
 
 Boston Emergency Medical Services said 80 people had visited its medical station on the Esplanade, requesting Tylenol, bandages, and ice packs. Ten people were taken to area hospitals, said spokeswoman McKenzie Ridings. 
 
 The buildup to the show began just after 7 p.m., with a series of blasts from a trio of small cannons positioned on the banks of the Charles River, drawing applause from the spectators. Governor Deval Patrick shot off one of the blasts and pumped his arms in the air. 
 
 Meanwhile, security at the Esplanade was tight, with several hundred state troopers, park rangers, and National Guard personnel patrolling the area. Troopers were both uniformed and in plainclothes, State Police spokesman David Procopio said. 
 
 Security measures included bag checks, limits on the sizes of coolers and tents, and a ban on glass containers and alcoholic beverages, he said. 
 
 In addition, Procopio said, State and Environmental Police were conducting marine patrols on the Charles, and a State Police Air Wing helicopter provided support from the air. 
 
 Bomb squads and hazardous materials teams were on standby. 
 
 By late Thursday night, State Police had not reported any arrests. 
 
 State Police did not have an estimate on the crowd late Thursday night, which was in the tens of thousands. 
 
 Traffic on the Southeast Expressway was standard for the evening rush hour, said Procopio, with the most significant backups on Interstate 93 southbound due to vehicles being rerouted around Storrow Drive, which was closed. 
 
 But on the Esplanade, the focus before the rain remained on the entertainment offerings and the camaraderie among strangers who gathered to mark the nation’s independence in an event that some people said is unrivaled by similar celebrations in other cities. 
 
 “I drive past D.C., I drive past Philadelphia, I drive past New York,” said T.C. Jones, 60, a Richmond, Va., resident who travels to Boston every year to celebrate the holiday. “This is the Fourth of July.” 
 
 Jones wore a red, white, and blue tie-dyed Red Sox shirt and recalled being stationed as an Army paratrooper at Fort Bragg in North Carolina when he first saw the legendary Arthur Fiedler conducting the Pops on television. He decided then that he would eventually make it to Boston. 
 
 And even after the rain soaked the crowd, some who attended still had a favorable assessment of the evening, including Adamarie Brini, 49, of Wakefield, who deemed the event “one to tell the grandkids about.” 
 
 “It ended on a bang, that’s for sure, people huddling in doorways,” Brini said. 
 
 “We got wet. No harm, no foul. We got to see the fireworks.” ||||| More than two dozen people were injured when a wood platform holding live fireworks tipped over, sending the pyrotechnics into a crowd at a Fourth of July show northwest of Los Angeles, authorities said Friday. 
 
 Between 8,000 and 10,000 revelers were settling into their seats for the fireworks extravaganza at a Simi Valley park Thursday night when the spectacle of lights that were supposed to be launched in the sky never took off. Instead, a bright plume of red and white bursts spread across the ground, injuring 28 people and sending others fleeing for safety. 
 
 Police were still investigating what led to the explosion, but they said early indications show a platform designed and built to hold the fireworks gave way. 
 
 "For some unknown reasons the structure that holds these ordinances collapsed and caused them to be firing into the crowd," Simi Valley police Cmdr. Stephanie Shannon. 
 
 Four people were listed in serious condition, but their injuries were not considered life-threatening. Sixteen more were taken to hospitals with minor to moderate injuries. The remainder were treated at the park where emergency crews, already on hand as a safety precaution, set up a triage area. 
 
 Meanwhile, a worker at a fireworks show in North Myrtle Beach, S.C., was injured Thursday evening when a shell exploded prematurely. The explosion at the Cherry Grove Pier caused the show to end early, after just six minutes, and left a hole in the pier. 
 
 In California, a video clip aired on KCAL-TV shows a pair of firework blasts at or near the ground. Another clip, posted on YouTube and shot from a distance, shows three ground-level bursts. The fireworks continue for almost another minute before stopping. 
 
 "There was a big boom, everybody started running down the street, people were screaming," Justice Allen, 17, of Simi Valley told the Los Angeles Times. "Everybody was just terrified. People hid in bushes." 
 
 Authorities estimate people were 900 feet away from where the fireworks were being launched. One police officer who ran into the crowd when the blasts occurred had shrapnel tear through his leather belt and his clothing, Shannon said. He had minor injuries to his back. 
 
 Shannon said most people responded admirably and left in an orderly fashion. A bomb squad was at the park to deactivate the remainder of the fireworks. 
 
 Shannon said the fireworks primarily shot in one direction. 
 
 "They are going to travel the same distance across the park as they would in the air," she said. "The ones that had actually ignited that had to run their fuse were going directly into the crowd." 
 
 The annual July Fourth celebration has been sponsored by the city and the local Rotary Club for the past 43 years. Shannon said she had no information about the company hired for the fireworks show. 
 
 Simi Valley, home to the Ronald Reagan Presidential Library, is about 40 miles northwest of Los Angeles.
– Noticed something a bit off about PBS' A Capitol Fourth broadcast Monday? So did hundreds of people who took to Facebook and Twitter, per NBC News. Though host Tom Bergeron initially laughed off concerns that the live concert and fireworks display over Washington would be rained out, per the Washington Post, the sky above the Capitol Building was foggy and overcast as the fireworks began. That made seeing the show a bit difficult—so PBS intervened. Mingled with misty footage of fireworks over the Capitol building, with scaffolding clearly visible, was stock footage of fireworks from previous celebrations. Viewers were quick to call out the "fraudulent" scheme—there was no disclaimer during the "live" broadcast—noting the stock footage showed a clear sky over the Capitol Building, and no scaffolding, per the Post. Afterward, the show admitted to showing "a combination of the best fireworks from this year and previous years" because of the poor conditions. "It was the patriotic thing to do," reads a tweet from the Capitol Fourth account. "We apologize for any confusion this may have caused." The apology didn't appease some, though. "How is using stock video patriotic?" one user wrote. "If I wanted that, I'd watch YouTube." (A Texas teen tried to make a "fireworks bomb" and paid a steep price.)